Draft: draft-ietf-anima-autonomic-control-plane

Commentary: I discovered that the .xml file had -13 in it , which made me think that I was editing a not - most - recent version . So I removed all the bad .xml files around . The point of using  is that there is history in .xml , and if you want a record of where things are , then make branches or tags . And there is n't a - file . I grabbed - from the DT and put it place , and deleted the others . I edited the ACP rfc822name definitions , moving the routing - subdomain out of the middle , since it 's actually not relevant to an implementor . Also fixed the description , because it 's something that the ACP simply uses ONCE ( at configuration time ) to generate the 48 - bit ULA . It ca n't generate it each time , because it has to keep track of which ACP spaces are in use , etc . I changed text around Vlong to name the first bit of the Node - Number as the " F " , for format , so that the description is more understandable .
Autonomic functions need a control plane to communicate, which
depends on some addressing and routing.  This Autonomic Management
and Control Plane should ideally be self-managing, and as independent
as possible of configuration.  This document defines such a plane and
calls it the "Autonomic Control Plane", with the primary use as a
control plane for autonomic functions.  It also serves as a "virtual
out of band channel" for OAM (Operations Administration and
Management) communications over a network that is secure and reliable
even when the network is not configured, or not misconfigured.
Autonomic functions need a control plane to communicate, which
depends on some addressing and routing.  This Autonomic Management
and Control Plane should ideally be self-managing, and as independent
as possible of configuration.  This document defines such a plane and
calls it the "Autonomic Control Plane", with the primary use as a
control plane for autonomic functions.  It also serves as a "virtual
out-of-band channel" for Operations Administration and Management
(OAM) communications over a network that is secure and reliable even
when the network is not configured, or misconfigured.
Autonomic functions need an autonomically built communications
infrastructure or network plane (there is no well-established name
for this).  This infrastructure needs to be secure, resilient and re-
usable by all autonomic functions.  Section 5 of RFC7575 introduces
that infrastructure and calls it the "Autonomic Control Plane" (ACP).
More descriptively it would be the "Autonomic communications
infrastructure for Management and Control".  For naming consistency
with that prior document, this document continues to use the name ACP
though.
Today, the management and control plane of networks typically runs in
the global routing table, which is dependent on correct configuration
and routing.  Misconfigurations or routing problems can therefore
disrupt management and control channels.  Traditionally, an out of
band network has been used to recover from such problems, or
personnel is sent on site to access devices through console ports
(craft ports).  However, both options are expensive.
Autonomic Networking is a concept of self-management: Autonomic
functions self-configure, and negotiate parameters and settings
across the network.  RFC7575 defines the fundamental ideas and design
goals of Autonomic Networking.  A gap analysis of Autonomic
Networking is given in RFC7576.  The reference architecture for
Autonomic Networking in the IETF is specified in the document I-
D.ietf-anima-reference-model.
Autonomic functions need an autonomically built communications
infrastructure.  This infrastructure needs to be secure, resilient
and re-usable by all autonomic functions.  Section 5 of RFC7575
introduces that infrastructure and calls it the Autonomic Control
Plane (ACP).  More descriptively it would be the "Autonomic
communications infrastructure for Management and Control".  For
naming consistency with that prior document, this document continues
to use the name ACP though.
Today, the management and control plane of networks typically uses a
routing and forwarding table which is dependent on correct
configuration and routing.  Misconfigurations or routing problems can
disrupt management and control channels.  Traditionally, an out-of-
band network has been used to avoid or allow recovery from such
problems, or personnel are sent on site to access devices through
out-of-band management ports (also called craft ports, serial
console, management ethernet port).  However, both options are
expensive.
This document describes a modular design for a self-forming, self-
managing and self-protecting "Autonomic Control Plane" (ACP) which is
a virtual in-band network designed to be as independent as possible
of configuration, addressing and routing problems.  The details how
this achieved are defined in self-creation.  The ACP is designed to
remains operational even in the presence of configuration errors,
addressing or routing issues, or where policy could inadvertently
affect connectivity of both data packets or control packets.
This document uses the term "data-plane" to refer to anything in the
network nodes that is not the ACP, and therefore considered to be
dependent on (mis-)configuration.  This data-plen includes both the
traditional forwarding-plane, as well as any pre-existing control-
plane, such as routing protocols that establish routing tables for
the forwarding plane.
This document describes a modular design for a self-forming, self-
managing and self-protecting Autonomic Control Plane (ACP), which is
a virtual in-band network designed to be as independent as possible
of configuration, addressing and routing problems.  The details how
this is achieved are described in self-creation.  The ACP is designed
to remain operational even in the presence of configuration errors,
addressing or routing issues, or where policy could inadvertently
affect connectivity of both data packets or control packets.
This document uses the term "Data-Plane" to refer to anything in the
network nodes that is not the ACP, and therefore considered to be
dependent on (mis-)configuration.  This Data-Plane includes both the
traditional forwarding-plane, as well as any pre-existing control-
plane, such as routing protocols that establish routing tables for
the forwarding plane.
Autonomic functions communicate over the ACP.  The ACP therefore
supports directly Autonomic Networking functions, as described in
I-D.ietf-anima-reference-model.  For example, GRASP I-D.ietf-
anima-grasp runs securely inside the ACP and depends on the ACP as
its "security and transport substrate".
This document describes these use cases for the ACP in usage, it
defines the requirements in requirements. overview gives an overview
how the ACP is constructed, and in self-creation the process is
defined in detail. acp-l2-switches defines how to support ACP on L2
switches. workarounds explains how non-ACP nodes and networks can be
integrated.  The following sections are non-normative: benefit
reviews benefits of the ACP (after all the details have been
defined), further provides additional explanations and describes
additional details or future work possibilities that where considered
not to be appropriate for standardization in this document but
nevertheless assumed to be helpful for candidate adopters of the ACP.
The ACP as defined in this document can be implemented and operated
without dependency against other components of autonomic networks
except for the GRASP protocol on which it depends.  The document I-
D.ietf-anima-stable-connectivity describes how the ACP alone can be
used to provide stable connectivity for autonomic and non-autonomic
OAM applications ("Operations Administration and Management").  It
also explains on how existing management solutions can leverage the
ACP in parallel with traditional management models, when to use the
ACP and, how to integrate IPv4 based management, etc.
Combining ACP with BRSKI ("Bootstrapping Remote Secure Key
Infrastructures", see I-D.ietf-anima-bootstrapping-keyinfra) results
in the "Autonomic Network Infrastructure" as defined in I-D.ietf-
anima-reference-model. which provides autonomic connectivity (from
ACP) with full secure zero touch bootstrap (from BRSKI).  The ANI
itself does not constitute an Autonomic Network, but it enables
building more or less autonomic networks on top of it - using either
centralized, SDN ("Software Defined Networking", see RFC7426) style
automation or distributed automation via ASA ("Autonomic Service
Agents") / "Autonomic Functions" - or a mixture of both.  See I-
D.ietf-anima-reference-model for more information.
Autonomic functions communicate over the ACP.  The ACP therefore
directly supports Autonomic Networking functions, as described in
I-D.ietf-anima-reference-model.  For example, Generic Autonomic
Signaling Protocol (GRASP - I-D.ietf-anima-grasp) runs securely
inside the ACP and depends on the ACP as its "security and
transport substrate".
A controller or network management system can use it to securely
bootstrap network devices in remote locations, even if the (Data-
Plane) network in between is not yet configured; no Data-Plane
dependent bootstrap configuration is required.  An example of such
a secure bootstrap process is described in I-D.ietf-anima-
bootstrapping-keyinfra.
This document describes these purposes as use cases for the ACP in
usage, it defines the requirements in requirements. overview gives an
overview how the ACP is constructed.
The normative part of this document starts with self-creation, where
the ACP is specified. acp-l2-switches defines normative how to
support ACP on L2 switches. workarounds explains normative how non-
ACP nodes and networks can be integrated.
The remaining sections are non-normative: benefit reviews benefits of
the ACP (after all the details have been defined), operational
provides operational recommendations, further provides additional
explanations and describes additional details or future standard or
propriety extensions that were considered not to be appropriate for
standardization in this document but were considered important to
document.  There are no dependencies against further to build a
complete working and interoperable ACP according to this document.
The ACP provides secure IPv6 connectivity, therefore it cannot only
be used as the secure connectivity for self-management as required
for the ACP in RFC7575, but it can also be used as the secure
connectivity for traditional (centralized) management.  The ACP can
be implemented and operated without any other components of autonomic
networks, except for the GRASP protocol which it leverages.
The document RFC8368 describes how the ACP alone can be used to
provide secure and stable connectivity for autonomic and non-
autonomic Operations Administration and Management (OAM)
applications.  That document also explains how existing management
solutions can leverage the ACP in parallel with traditional
management models, when to use the ACP and how to integrate with
potentially IPv4 only OAM backends.
Combining ACP with Bootstrapping Remote Secure Key Infrastructures
(BRSKI), see I-D.ietf-anima-bootstrapping-keyinfra) results in the
"Autonomic Network Infrastructure" as defined in I-D.ietf-anima-
reference-model, which provides autonomic connectivity (from ACP)
with fully secure zero-touch (automated) bootstrap from BRSKI.  The
ANI itself does not constitute an Autonomic Network, but it allows
the building of more or less autonomic networks on top of it - using
either centralized, Software Defined Networking- (SDN-)style (see
RFC7426) automation or distributed automation via Autonomic Service
Agents (ASA) / Autonomic Functions (AF) - or a mixture of both.  See
I-D.ietf-anima-reference-model for more information.
Please see the following Terminology section (terminology) for
explanations of terms used in this section.
The design of the ACP as defined in this document is considered to be
applicable to all types of "professionally managed" networks: Service
Provider, Local Area Network (LAN), Metro(politan networks), Wide
Area Network (WAN), Enterprise Information Technology (IT) and ot
(OT) networks.  The ACP can operate equally on layer 3 equipment and
on layer 2 equipment such a bridges (see acp-l2-switches).  The
encryption mechanism used by the ACP is defined to be negotiable,
therefore it can be extended to environments with different
encryption protocol preferences.  The minimum implementation
requirements in this document attempt to achieve maximum
interoperability by requiring support for few options: IP security
(IPsec), see RFC4301) and datagram Transport Layer Security version
1.2 (DTLS), see RFC6347), depending on type of device.
The implementation footprint of the ACP consists of Public Key
Infrastructure (PKI) code for the ACP certificate, the GRASP
protocol, UDP, TCP and TLS (for security and reliability of GRASP),
the ACP secure channel protocol used (such as IPsec or DTLS), and an
instance of IPv6 packet forwarding and routing via the Routing
Protocol for Low-power and Lossy Networks (RPL), see RFC6550, that is
separate from routing and forwarding for the Data-Plane (user
traffic).
The ACP uses only IPv6 to avoid complexity of dual-stack ACP
operations (IPv6/IPv4).  Nevertheless, it can without any changes be
integrated into even otherwise IPv4-only network devices.  The Data-
Plane itself would not need to change, it could continue to be IPv4
only.  For such IPv4 only devices, the IPv6 protocol itself would be
additional implementation footprint only used for the ACP.
RPL was chosen because it requires a smaller routing table footprint
in large networks compared to other routing protocols with an
autonomically configured single area.  The deployment experience of
large scale Internet of Things (IoT) networks serves as the basis for
wide deployment experience with RPL.  The profile chosen for RPL in
the ACP does not leverage any RPL specific forwarding plane features
(IPv6 extension headers), making its implementation a pure control
plane software requirement.
GRASP is the only completely novel protocol used in the ACP, and this
choice was necessary because there is no existing suitable protocol
to provide the necessary functions to the ACP, so GRASP was developed
to fill that gap.
The ACP design can be applicable to (cpu, memory) constrained devices
and (bitrate, reliability) constrained networks, but this document
does not attempt to define the most constrained type of devices or
networks to which the ACP is applicable.  RPL and DTLS are two
protocol choices already making ACP more applicable to constrained
environments.  See reuse-acp for discussions about how future
standards or proprietary extensions/variations of the ACP could
better meet different expectations from those on which the current
design is based.
"Autonomic Control Plane".  The Autonomic Function as defined in
this document.  It provides secure zero-touch transitive (network
wide) IPv6 connectivity for all nodes in the same ACP domain as
well as a GRASP instance running across this ACP IPv6
connectivity.  The ACP is primarily meant to be used as a
component of the ANI to enable Autonomic Networks but it can
equally be used in simple ANI networks (with no other Autonomic
Functions) or completely by itself.
"Autonomic Control Plane".  The Autonomic Function as defined in
this document.  It provides secure zero-touch (automated)
transitive (network wide) IPv6 connectivity for all nodes in the
same ACP domain as well as a GRASP instance running across this
ACP IPv6 connectivity.  The ACP is primarily meant to be used as a
component of the ANI to enable Autonomic Networks but it can
equally be used in simple ANI networks (with no other Autonomic
Functions) or completely by itself.
The ACP domain is the set of nodes with domain certificates that
allow them to authenticate each other as members of the ACP
domain.  See certcheck.
An rfc822Name information element (e.g.: field) in the domain
certificate in which the ACP relevant information is encoded: the
domain name and the ACP address.
The loopback interface in the ACP VRF that has the ACP address
assigned to it.
The prefixes routed across the ACP.  In the normal/simple case,
the ACP has one ULA prefix, see addressing.  The ACP routing table
may include multiple ULA prefixes if the "rsub" option is used to
create addresses from more than one ULA prefix.  See domcert-
acpinfo.  The ACP may also include non-ULA prefixes if those are
configured on ACP connect interfaces.  See NMS.
A security association established hop-by-hop between adjacent ACP
nodes to carry traffic of the ACP VRF separated from data-plane
traffic in-band over the same links as the data-plane.
The protocol used to build an ACP secure channel, e.g.: IKEv2/
IPsec or dTLS.
The ACP domain is the set of nodes with domcert-def that allow
them to authenticate each other as members of the ACP domain.  See
also certcheck.
A provisioned RFC5280 certificate (LDevID) carrying the domain
information field which is used by the ACP to learn its address in
the ACP and to derive and cryptographically assert its membership
in the ACP domain.
An rfc822Name information element (e.g., field) in the domain
certificate in which the ACP relevant information is encoded: the
domain name and the ACP address.
The Loopback interface in the ACP Virtual Routing and Forwarding
(VRF) that has the ACP address assigned to it.
The /48 IPv6 address prefixes used across the ACP.  In the normal/
simple case, the ACP has one ULA prefix, see addressing.  The ACP
routing table may include multiple ULA prefixes if the "rsub"
option is used to create addresses from more than one ULA prefix.
See domcert-acpinfo.  The ACP may also include non-ULA prefixes if
those are configured on ACP connect interfaces.  See NMS.
A cryptographically authenticated and encrypted data connection
established between (normally) adjacent ACP nodes to carry traffic
of the ACP VRF secure and isolated from Data-Plane traffic in-band
over the same link/path as the Data-Plane.
The protocol used to build an ACP secure channel, e.g., Internet
Key Exchange Protocol version 2 (IKEv2) with IPsec or Datagram
Transport Layer Security (DTLS).
"Autonomic Network Infrastructure".  The ANI is the infrastructure
to enable Autonomic Networks.  It includes ACP, BRSKI and GRASP.
Every Autonomic Network includes the ANI, but not every ANI
network needs to include autonomic functions beyond the ANI (nor
intent).  An ANI network without further autonomic functions can
for example support secure zero touch bootstrap and stable
connectivity for SDN networks - see I-D.ietf-anima-stable-
connectivity.
"Autonomic Network Infrastructure".  The ANI is the infrastructure
to enable Autonomic Networks.  It includes ACP, BRSKI and GRASP.
Every Autonomic Network includes the ANI, but not every ANI
network needs to include autonomic functions beyond the ANI (nor
Intent).  An ANI network without further autonomic functions can
for example support secure zero-touch (automated) bootstrap and
stable connectivity for SDN networks - see RFC8368.
"Bootstrapping Remote Secure Key Infrastructures" (I-D.ietf-anima-
bootstrapping-keyinfra.  A protocol extending EST to enable secure
zero touch bootstrap in conjunction with ACP.  ANI nodes use ACP,
BRSKI and GRASP.
A provisioned certificate (LDevID) carrying the domain information
field which is used by the ACP to learn its address in the ACP and
to derive and cryptographically assert its membership in the ACP
domain.
"Bootstrapping Remote Secure Key Infrastructures" (I-D.ietf-anima-
bootstrapping-keyinfra.  A protocol extending EST to enable secure
zero-touch bootstrap in conjunction with ACP.  ANI nodes use ACP,
BRSKI and GRASP.
"Generic Autonomic Signaling Protocol".  An extensible signaling
protocol required by the ACP for ACP neighbor discovery.  The ACP
also provides the "security and transport substrate" for the "ACP
instance of GRASP" which is run inside the ACP to support BRSKI
and other future Autonomic Functions.  See I-D.ietf-anima-grasp.
An "Initial Device IDentity" X.509 certificate installed by the
vendor on new equipment.  Contains information that establishes
the identity of the node in the context of its vendor/manufacturer
such as device model/type and serial number.  See AR8021.
Northbound operator and automation facing interface of an
Autonomic Network according to I-D.ietf-anima-reference-model.
"Generic Autonomic Signaling Protocol".  An extensible signaling
protocol required by the ACP for ACP neighbor discovery.  The ACP
also provides the "security and transport substrate" for the "ACP
instance of GRASP".  This instance of GRASP runs across the ACP
secure channels to support BRSKI and other NOC/OAM or Autonomic
Functions.  See I-D.ietf-anima-grasp.
An "Initial Device IDentity" X.509 certificate installed by the
vendor on new equipment.  Contains information that establishes
the identity of the node in the context of its vendor/manufacturer
such as device model/type and serial number.  See AR8021.  IDevID
cannot be used for the ACP because they are not provisioned by the
owner of the network, so they can not directly indicate an ACP
domain they belong to.
The type of management used predominantly in IP based networks,
not leveraging an out-of-band-def.  In in-band management, access
to the managed equipment depends on the configuration of this
equipment itself: interface, addressing, forwarding, routing,
policy, security, management.  This dependency makes in-band
management fragile because the configuration actions performed may
break in-band management connectivity.  Breakage can not only be
unintentional, it can simply be an unavoidable side effect of
being unable to create configuration schemes where in-band
management connectivity configuration is unaffected by Data-Plane
configuration.  See also out-of-band-def.
Policy language of an autonomic network according to I-D.ietf-
anima-reference-model.
A system, e.g.: supporting the ACP according to this document.
Can be virtual or physical.  Physical nodes are called devices.
"IPv6 Routing Protocol for Low-Power and Lossy Networks".  The
routing protocol used in the ACP.
A system, e.g., supporting the ACP according to this document.
Can be virtual or physical.  Physical nodes are called devices.
The identifier of an ACP node inside that ACP.  It is the last 64
(see zone-scheme) or 78-bits (see Vlong) of the ACP address.
"https://en.wikipedia.org/wiki/Operational_Technology" [1]: "The
hardware and software dedicated to detecting or causing changes in
physical processes through direct monitoring and/or control of
physical devices such as valves, pumps, etc.".  OT networks are
today in most cases well separated from Information Technology
(IT) networks.
An out-of-band network is a secondary network used to manage a
primary network.  The equipment of the primary network is
connected to the out-of-band network via dedicated management
ports on the primary network equipment.  Serial (console)
management ports were historically most common, higher end network
equipment now also has ethernet ports dedicated only for
management.  An out-of-band network provides management access to
the primary network independent of the configuration state of the
primary network.  One of the goals of the ACP is to provide this
benefit of out-of-band networks virtually on the primary network
equipment.  The ACP VRF acts as a virtual out of band network
device providing configuration independent management access.  The
ACP secure channels are the virtual links of the ACP virtual out-
of-band network, meant to be operating independent of the
configuration of the primary network.  See also in-band-def.
"IPv6 Routing Protocol for Low-Power and Lossy Networks".  The
routing protocol used in the ACP.  See RFC6550.
An ACP registrar is an entity (software and/or person) that is
orchestrating the enrollment of ACP nodes with the ACP domain
certificate.  ANI nodes use BRSKI, so ANI registrars are also
called BRSKI registrars.  For non-ANI ACP nodes, the registrar
mechanisms are undefined by this document.  See acp-registrars.
Renewal and other maintenance (such as revocation) of ACP domain
certificates may be performed by other entities than registrars.
EST must be supported for ACP domain certificate renewal (see
domcert-maint).  BRSKI is an extension of EST, so ANI/BRSKI
registrars can easily support ACP domain certificate renewal in
addition to initial enrollment.
A "Unique Local Address" (ULA) is an IPv6 address in the block
fc00::/7, defined in RFC4193.  It is the approximate IPv6
counterpart of the IPv4 private address (RFC1918).
The ACP is modelled in this document as a "Virtual Routing and
Forwarding" instance (VRF).  This means that it is based on a
"virtual router" consisting of a separate IPv6 forwarding table to
which the ACP virtual interfaces are attached and an associated
separate IPv6 routing table.  Unlike the VRFs on MPLS/VPN-PE
(RFC4364) or LISP XTR (RFC6830), the ACP VRF does not have any
special "core facing" functionality or routing/mapping protocols
shared across multiple VRFs.  In vendor products a VRF such as the
ACP-VRF may also be referred to as a so called VRF-lite.
An ACP zone is a connected region of the ACP where nodes derive
from their non-aggregatable ACP address (identifier address) an
aggregateable ACP zone address (locator address).  See the
definition of the ACP Zone Addressing Sub-Scheme (zone-scheme).
The complete definition of zones is subject to future work because
this document does not describe the routing protocols details for
aggregation of ACP zone addresses, but only their addressing
scheme.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
RFC2119 when they appear in ALL CAPS.  When these words are not in
ALL CAPS (such as "should" or "Should"), they have their usual
English meanings, and are not to be interpreted as RFC2119 key words.
A "Unique Local Address" (ULA) is an IPv6 address in the block
fc00::/7, defined in RFC4193.  It is the approximate IPv6
counterpart of the IPv4 private address (RFC1918).  The ULA Global
ID prefix are the first 48-bits of a ULA address.  In this
document it is abbreviated as "ULA prefix".
The ACP is modeled in this document as a "Virtual Routing and
Forwarding" instance (VRF).  This means that it is based on a
"virtual router" consisting of a separate IPv6 forwarding table to
which the ACP virtual interfaces are attached and an associated
IPv6 routing table separate from the Data-Plane.  Unlike the VRFs
on MPLS/VPN-PE (RFC4364) or LISP XTR (RFC6830), the ACP VRF does
not have any special "core facing" functionality or routing/
mapping protocols shared across multiple VRFs.  In vendor products
a VRF such as the ACP-VRF may also be referred to as a so called
VRF-lite.
An ACP zone is a set of ACP nodes using the same zone field value
in their ACP address according to zone-scheme.  Zones are a
mechanism to support structured addressing of ACP addresses within
the same /48-bit ULA prefix.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119],[RFC8174] when, and only when, they appear in all
capitals, as shown here.
Autonomic Functions need a stable infrastructure to run on, and all
autonomic functions should use the same infrastructure to minimize
the complexity of the network.  This way, there is only need for a
single discovery mechanism, a single security mechanism, and other
processes that distributed functions require.
Autonomic Functions need a stable infrastructure to run on, and all
autonomic functions should use the same infrastructure to minimize
the complexity of the network.  In this way, there is only need for a
single discovery mechanism, a single security mechanism, and single
instances of other processes that distributed functions require.
Today, bootstrapping a new node typically requires all nodes between
a controlling node such as an SDN controller ("Software Defined
Networking", see RFC7426) and the new node to be completely and
correctly addressed, configured and secured.  Bootstrapping and
configuration of a network happens in rings around the controller -
configuring each ring of devices before the next one can be
bootstrapped.  Without console access (for example through an out of
band network) it is not possible today to make devices securely
reachable before having configured the entire network leading up to
them.
With the ACP, secure bootstrap of new devices can happen without
requiring any configuration such as the transit connectivity to
bootstrap further devices.  A new device can automatically be
bootstrapped in a secure fashion and be deployed with a domain
certificate.  This does not require any configuration on intermediate
nodes, because they can communicate zero-touch and securely through
the ACP.
Today, most critical control plane protocols and network management
protocols are running in the data-plane (global routing table) of the
network.  This leads to undesirable dependencies between control and
management plane on one side and the data-plane on the other: Only if
the data-plane is operational, will the other planes work as
expected.
Data-plane connectivity can be affected by errors and faults, for
example misconfigurations that make AAA (Authentication,
Authorization and Accounting) servers unreachable can lock an
administrator out of a device; routing or addressing issues can make
a device unreachable; shutting down interfaces over which a current
management session is running can lock an admin irreversibly out of
the device.  Traditionally only console access can help recover from
such issues.
Data-plane dependencies also affect applications in a NOC ("Network
Operations Center") such as SDN controller applications: Certain
network changes are today hard to operate, because the change itself
may affect reachability of the devices.  Examples are address or mask
changes, routing changes, or security policies.  Today such changes
require precise hop-by-hop planning.
For management plane protocols, the ACP provides the functionality
of a "Virtual-out-of-band (VooB) channel", by providing
connectivity to all nodes regardless of their configuration or
global routing table.
The document I-D.ietf-anima-stable-connectivity explains the use
cases for the ACP in significantly more detail and explains how the
ACP can be used in practical network operations.
The ACP SHOULD provide robust connectivity: As far as possible, it
should be independent of configured addressing, configuration and
routing.  Requirements 2 and 3 build on this requirement, but also
have value on their own.
The ACP MUST have a separate address space from the data-plane.
Reason: traceability, debug-ability, separation from data-plane,
security (can block easily at edge).
The ACP MUST use autonomically managed address space.  Reason:
easy bootstrap and setup ("autonomic"); robustness (admin can't
mess things up so easily).  This document suggests to use ULA
addressing for this purpose ("Unique Local Address", see RFC4193).
The ACP MUST be generic.  Usable by all the functions and
protocols of the AN infrastructure.  Clients of the ACP MUST NOT
be tied to a particular application or transport protocol.
The ACP MUST provide security: Messages coming through the ACP
MUST be authenticated to be from a trusted node, and SHOULD (very
strong SHOULD) be encrypted.
Today, bootstrapping a new node typically requires all nodes between
a controlling node such as an SDN controller ("Software Defined
Networking", see RFC7426) and the new node to be completely and
correctly addressed, configured and secured.  Bootstrapping and
configuration of a network happens in rings around the controller -
configuring each ring of devices before the next one can be
bootstrapped.  Without console access (for example through an out-of-
band network) it is not possible today to make devices securely
reachable before having configured the entire network leading up to
them.
With the ACP, secure bootstrap of new devices and whole new networks
can happen without requiring any configuration of unconfigured
devices along the path: As long as all devices along the path support
ACP and a zero-touch bootstrap mechanism such as BRSKI, the ACP
across a whole network of unconfigured devices can be brought up
without operator/provisioning intervention.  The ACP also provides
additional security for any bootstrap mechanism, because it encrypts
the traffic along the path hop-by-hop.
Today, most critical control plane protocols and network management
protocols are using the Data-Plane of the network.  This leads to
often undesirable dependencies between control and management plane
on one side and the Data-Plane on the other: Only if the forwarding
and control plane of the Data-Plane are configured correctly, will
the Data-Plane and the management plane work as expected.
Data-Plane connectivity can be affected by errors and faults, for
example misconfigurations that make AAA (Authentication,
Authorization and Accounting) servers unreachable or can lock an
administrator out of a device; routing or addressing issues can make
a device unreachable; shutting down interfaces over which a current
management session is running can lock an admin irreversibly out of
the device.  Traditionally only out-of-band access can help recover
from such issues (such as serial console or ethernet management
port).
Data-Plane dependencies also affect applications in a Network
Operations Center (NOC) such as SDN controller applications: Certain
network changes are today hard to implement, because the change
itself may affect reachability of the devices.  Examples are address
or mask changes, routing changes, or security policies.  Today such
changes require precise hop-by-hop planning.
Note that specific control plane functions for the Data-Plane often
want to depend on forwarding of their packets via the Data-Plane:
Aliveness and routing protocol signaling packets across the Data-
Plane to verify reachability across the Data-Plane, using IPv4
signaling packets for IPv4 routing vs. IPv6 signaling packets for
IPv6 routing.
For management plane protocols, the ACP provides the functionality
of a Virtual out-of-band (VooB) channel, by providing connectivity
to all nodes regardless of their Data-Plane configuration, routing
and forwarding tables.
The document RFC8368 explains this use case for the ACP in
significantly more detail and explains how the ACP can be used in
practical network operations.
The ACP _SHOULD_ provide robust connectivity: As far as possible,
it should be independent of configured addressing, configuration
and routing.  Requirements 2 and 3 build on this requirement, but
also have value on their own.
The ACP _MUST_ have a separate address space from the Data-Plane.
Reason: traceability, debug-ability, separation from Data-Plane,
infrastructure security (filtering based on known address space).
The ACP _MUST_ use autonomically managed address space.  Reason:
easy bootstrap and setup ("autonomic"); robustness (admin can't
mess things up so easily).  This document suggests using ULA
addressing for this purpose ("Unique Local Address", see RFC4193).
The ACP _MUST_ be generic, that is it MUST be usable by all the
functions and protocols of the ANI.  Clients of the ACP MUST NOT
be tied to a particular application or transport protocol.
The ACP _MUST_ provide security: Messages coming through the ACP
MUST be authenticated to be from a trusted node, and SHOULD (very
strong SHOULD) be encrypted.
Explanation for ACP4: In a fully autonomic network (AN), newly
written ASA could potentially all communicate exclusively via GRASP
with each other, and if that was assumed to be the only requirement
against the ACP, it would not need to provide IPv6 layer connectivity
between nodes, but only GRASP connectivity.  Nevertheless, because
ACP also intends to support non-AN networks, it is crucial to support
IPv6 layer connectivity across the ACP to support any transport and
application layer protocols.
An ACP node creates a VRF ("Virtual Routing and Forwarding")
instance, or a similar virtual context.
An ACP node creates a Virtual Routing and Forwarding (VRF)
instance, or a similar virtual context.
Inside the ACP VRF, each node sets up a loopback interface with
its ULA IPv6 address.
Inside the ACP VRF, each node assigns its ULA IPv6 address to a
Loopback interface assigned to the ACP VRF.
Connecting over non-ACP Layer-3 clouds initially requires a tunnel
between ACP nodes.
Connecting over non-ACP Layer-3 clouds requires explicit
configuration.  See remote-acp-neighbors.
The resulting overlay network is normally based exclusively on hop-
by-hop tunnels.  This is because addressing used on links is IPv6
link local addressing, which does not require any prior set-up.  This
way the ACP can be built even if there is no configuration on the
node, or if the data-plane has issues such as addressing or routing
problems.
ACP relies on group security.  An ACP domain is a group of nodes that
trust each other to participate in ACP operations.  To establish
trust, the ACP requires certificates: An ACP node MUST have keying
material consisting of a certificate (LDevID), with which it can
cryptographically assert its membership in the ACP domain and trust
anchor(s) associated with that certificate with which it can verify
the membership of other nodes (see certcheck).  The certificate is
called the ACP domain certificate, the trust anchor(s) are the CA
("Certificate Authority") of the ACP domain.
The resulting overlay network is normally based exclusively on hop-
by-hop tunnels.  This is because addressing used on links is IPv6
link local addressing, which does not require any prior set-up.  In
this way the ACP can be built even if there is no configuration on
the node, or if the Data-Plane has issues such as addressing or
routing problems.
The ACP relies on group security.  An ACP domain is a group of nodes
that trust each other to participate in ACP operations.  To establish
trust, each ACP member requires keying material: An ACP node MUST
have a certificate (LDevID) and a Trust Anchor (TA) consisting of a
certificate (chain) used to sign the LDevID of all ACP domain
members.  The LDevID is used to cryptographically authenticate the
membership of its owner node in the ACP domain to other ACP domain
members, the TA is used to authenticate the ACP domain membership of
other nodes (see certcheck).
The LDevID is called the ACP domain certificate, the TA is the
Certificate Authority (CA) of the ACP domain.
Note: LDevID ("Local Device IDentification") is the term used to
indicate a certificate that was provisioned by the owner of a node as
opposed to IDevID ("Initial Device IDentifier") that may has been
loaded on the node during manufacturing time.  Those IDevID do not
include owner and deployment specific information to allows autonomic
establishment of trust for the operations of an ACP domain (e.g.:
between two ACP nodes without relying on any third party).
This document uses the term ACP in many places where the Autonomic
Networking reference documents RFC7575 and I-D.ietf-anima-reference-
model use the word autonomic.  This is done because those reference
documents consider (only) fully autonomic networks and nodes, but
support of ACP does not require support for other components of
autonomic networks.  Therefore the word autonomic might be misleading
to operators interested in only the ACP.
RFC7575 defines the term "Autonomic Domain" as a collection of
autonomic nodes.  ACP nodes do not need to be fully autonomic, but
when they are, then the ACP domain is an autonomic domain.  Likewise,
I-D.ietf-anima-reference-model defines the term "Domain Certificate"
as the certificate used in an autonomic domain.  The ACP domain
certificate is that domain certificate when ACP nodes are (fully)
autonomic nodes.  Finally, this document uses the term ACP network to
refer to the network created by active ACP nodes in an ACP domain.
The ACP network itself can extend beyond ACP nodes through the
mechanisms described in ACPconnect).
The ACP domain certificate can and should be used for any
authentication between ACP nodes where the required security is
domain membership. certcheck defines this "ACP domain membership
check".  The uses of this check that are standardized in this
document are for the establishment of ACP secure channels
(neighbor_verification) and for ACP GRASP (GRASP-substrate).  Other
uses are subject to future work, but it is recommended that it is the
default security check for any end-to-end connections between ASA.
It is equally useable by other functions such as legacy OAM
functions.
RFC7575 defines the term "Autonomic Domain" as a collection of
autonomic nodes.  ACP nodes do not need to be fully autonomic, but
when they are, then the ACP domain is an autonomic domain.  Likewise,
I-D.ietf-anima-reference-model defines the term "Domain Certificate"
as the certificate used in an autonomic domain.  The ACP domain
certificate is that domain certificate when ACP nodes are (fully)
autonomic nodes.  Finally, this document uses the term ACP network to
refer to the network created by active ACP nodes in an ACP domain.
The ACP network itself can extend beyond ACP nodes through the
mechanisms described in ACPconnect.
The ACP domain certificate SHOULD be used for any authentication
between nodes with ACP domain certificates (ACP nodes and NOC nodes)
where the required condition is ACP domain membership, such as ACP
node to NOC/OAM end-to-end security and ASA to ASA end-to-end
security. certcheck defines this "ACP domain membership check".  The
uses of this check that are standardized in this document are for the
establishment of ACP secure channels (neighbor_verification) and for
ACP GRASP (GRASP-substrate).
"acp-address" MUST be the ACP address of the node.  It is optional to
support variations of the ACP mechanisms, for example other means for
nodes to assign ACP addresses to themselves.  Such methods are
subject to future work though.
Note: "acp-address" cannot use standard IPv6 address formats because
it must match the simple dot-atom format of RFC5322.  ":" are not
allowed in that format.
"domain" is used to indicate the ACP Domain.  ACP members with the
same ACP Domain trust each other (authenticated by being signed by a
trusted CA), and are authorized to build ACP channels with each
other.  See certcheck.  Domain SHOULD be the FQDN of a domain owned
by the operator assigning the certificate.  This is a simple method
to ensure that the domain is globally unique and collision of ACP
addresses would therefore only happen due to ULA hash collisions.  If
the operator does not own any FQDN, it should choose a string in FQDN
format that intends to be equally unique.
"routing-subdomain" is the autonomic subdomain that is used by
Registrar(s) within the same ACP domain to calculate the hash for the
ULA prefix of the ACP address of the network.  This is a recommended
heuristic. "rsub" is optional; its syntax is defined in this
document, but its semantics are for further study.  Understanding the
benefits of using rsub may depend on the results of future work on
enhancing routing for the ACP.  When "rsub" is not used, "routing-
subdomain" is the same as "domain".
The optional "extensions" field is used for future extensions to this
specification.  It MUST be ignored if present and not understood.
Note that the maximum size of "domain-information" is 254 characters
and the maximum size of node-info is 64 characters according to
RFC5280 that is referring to RFC2821 (superseded by RFC5321).
There are a wide range of pre-existing protocols/services where
authentication with LDevID is desirable.  Enrolling and
maintaining separate LDevIDs for each of these protocols/services
is often undesirable overhead.  Therefore, the information element
required for the ACP in the domain certificate should be encoded
in a way that minimizes the possibility of creating
incompatibilities with such other uses beside the authentication
for the ACP.
The elements in the LDevID required for the ACP should not cause
incompatibilities with any pre-existing ASN.1 software potentially
in use in those other pre-existing SW systems.  This eliminates
the use of novel information elements because those require
extensions to those pre-existing ASN.1 parsers.
The elements in the LDevID required for the ACP should also not be
misinterpreted by any pre-existing protocol/service that might use
the LDevID.  If the elements used for the ACP are interpreted by
other protocols/services, then the impact should be benign.
Using an IP address format encoding could result in non-benign
misinterpretation of the domain information field; other protocol/
services unaware of the ACP could try to do something with the ACP
address that would fail to work correctly.  For example, the
address could be interpreted to be an address of the node in a VRF
other than the ACP VRF.
Nodes complying with this specification MUST be able to receive their
ACP address through the domain certificate, in which case their own
ACP domain certificate MUST have the 32hex-dig "acp-address" field.
Nodes complying with this specification MUST also be able to
authenticate nodes as ACP domain members / ACP secure channel peers
when they have an empty or 0-value acp-address field.  See certcheck.
"acp-domain-name" is used to indicate the ACP Domain across which all
ACP nodes trust each other and are willing to build ACP channels to
each other.  See certcheck.  Acp-domain-name SHOULD be the FQDN of a
DNS domain owned by the operator assigning the certificate.  This is
a simple method to ensure that the domain is globally unique and
collision of ACP addresses would therefore only happen due to ULA
hash collisions.  If the operator does not own any FQDN, it should
choose a string (in FQDN format) that it intends to be equally
unique.
"routing-subdomain" is a heuristic that allows a Registrar to
consistently generate a unique 48-bit ULA prefix for ACP addresses.
The presence of the "rsub" component allows to a single ACP domain to
employ multiple /48 ULA prefixes.  See domain-usage for example use-
cases.
The optional "extensions" field is used for future standardized
extensions to this specification.  It MUST be ignored if present and
not understood.
"rsub" needs to be in the "local-part": If the format just had
routing-subdomain as the domain part of the domain-information,
rsub and acp-domain-name could not be separated from each other.
It also makes acp-domain-name a valid e-mail target across all
routing-subdomains.
"acp-address" cannot use standard IPv6 address formats because it
must match the simple dot-atom format of RFC5322.  The character
":" is not allowed in that format.
If "acp-address" is empty, and "rsub" is empty too, the "local-
part" will have the format "rfcSELF + + extension(s)".  The two
plus characters are necessary so the node can unambiguously parse
that both "acp-address" and "rsub" are empty.
The maximum size of "domain-information" is 254 characters and the
maximum size of node-info is 64 characters according to RFC5280
that is referring to RFC2821 (superseded by RFC5321).
It should be possible to share the LDevID with other uses beside
the ACP.  Therefore, the information element required for the ACP
should be encoded so that it minimizes the possibility of creating
incompatibilities with such other uses.
The information for the ACP should not cause incompatibilities
with any pre-existing ASN.1 software.  This eliminates the
introduction of a novel information element because that could
require extensions to such pre-existing ASN.1 parsers.
The element required for the ACP should not be misinterpreted by
any other uses of the LDevID.  If the element used for the ACP is
interpreted by other uses, the impact should be benign.
Using an IP address format encoding could result in non-benign
misinterpretation of the domain information field; other uses
unaware of the ACP could try to do something with the ACP address
that would fail to work correctly.  For example, the address could
be interpreted to be an address of the node which does not belong
to the ACP VRF.
rfc822Name encoding is quite flexible.  We choose to encode the
full ACP address AND the domain name with sub part into a single
rfc822Name information element it, so that it is easier to
examine/use the "domain information field".
rfc822Name encoding is quite flexible.  The ACP information field
encodes the full ACP address AND the domain name with rsub part,
so that it is easier to examine/use the "domain information
field".
The peer certificate is valid as proven by the security
associations protocol exchange.
The peers certificate is signed by one of the trust anchors
associated with the ACP domain certificate.
If the node certificates indicate a CDP (or OCSP) then the peer's
certificate must be valid according to those criteria. e.g.: OCSP
check across the ACP or not listed in the CRL retrieved from the
CDP.
The peers certificate has a syntactically valid domain information
field (subjectAltName / rfc822Name) and the domain name in that
peers domain information field is the same as in this ACP node
certificate.  Note that future Intent rules may modify this.  See
domain-usage.
ACP nodes MUST support certificate renewal via EST ("Enrollment over
Secure Transport", see RFC7030) and MAY support other mechanisms.  An
ACP network MUST have at least one ACP node supporting EST server
functionality across the ACP so that EST renewal is useable.  The
mechanism by which the domain certificate was initially provisioned
SHOULD provide a mechanism to store the URL of one EST server with
its ACP address into the node for later renewal.  This server does
not have to be the same as the one performing the initial certificate
enrolment.
The objective value "SRV.est" indicates that the objective is an
RFC7030 compliant EST server because "est" is an RFC6335 registered
service name for RFC7030.  Future backward compatible extensions/
alternatives to RFC7030 may be indicated through objective-value.
Future non-backward compatible certificate renewal options must use a
different objective-name.
The M_FLOOD message MUST be sent periodically.  The default SHOULD be
60 seconds, the value SHOULD be operator configurable.  It must be so
high that the aggregate amount of periodic M_FLOODs from all flooded
objectives causes only negligible traffic across the ACP.  The ttl
parameter SHOULD be 3.5 times the period so that up to three
consecutive messages can be dropped before considering an
announcement expired.  In the example above, the ttl is 210000 msec,
3.5 times 60 seconds.
Domain certificates SHOULD by default be renewed 50% into their
lifetime.  When performing renewal, the node SHOULD attempt to
connect to the remembered EST server.  If that fails, it SHOULD
attempt to connect to EST server(s) learned via GRASP.  The server
with which certificate renewal succeeds SHOULD be remembered for the
next renewal.
The ACP node MUST support CRLs ("Certificate Revocation Lists") via
HTTPs from one or more CDPs ("CRL Distribution Points").  These CDPs
MUST be indicated in the Domain Certificate when used.  If the CDP
URL uses an IPv6 ULA, the ACP node will try to reach it via the ACP.
In that case the ACP address in the domain certificate of the CDP as
learned by the ACP node during the HTTPs TLS handshake SHOULD match
that ULA address in the HTTPs URL.
Renewal of certificates SHOULD start after less than 50% of the
domain certificate lifetime so that network operations has ample time
to investigate and resolve any problems that cause a node to not
renew its domain certificate in time - and to allow prolonged periods
of running parts of a network disconnected from any CA.
Certificate lifetime should be set to be as short as feasible.  Given
how certificate renewal is fully automated via ACP and EST, the
primarily limiting factor for shorter certificate lifetimes (than the
typical one year) is load on the EST server(s) and CA.  It is
therefore recommended that ACP domain certificates are managed via a
CA chain where the assigning CA has enough performance to manage
short lived certificates.
To know to which nodes to establish an ACP channel, every ACP node
maintains an adjacency table.  The adjacency table contains
information about adjacent ACP nodes, at a minimum: Node-ID,
interface on which neighbor was discovered (by GRASP as explained
below), link-local IPv6 address of neighbor on that interface,
certificate (including domain information field).  An ACP node MUST
maintain this adjacency table up to date.  This table is used to
determine to which neighbor an ACP connection is established.
Where the next ACP node is not directly adjacent, the information in
the adjacency table can be supplemented by configuration.  For
example, the node-ID and IP address could be configured.
The peer certificate is valid (lifetime).
The peer has proved ownership of the private key associated with
the certificate's public key.
The peer's certificate is signed by one of the trust anchors
associated with the ACP domain certificate.
If the node certificate indicates a Certificate Revocation List
(CRL) Distribution Point (CDP) (RFC5280, section 4.2.1.13) or
Online Certificate Status Protocol (OCSP) responder (RFC5280,
section 4.2.2.1), then the peer's certificate must be valid
according to those criteria: An OCSP check for the peer's
certificate across the ACP must succeed or the peer certificate
must not be listed in the CRL retrieved from the CDP.
The peer's certificate has a syntactically valid ACP domain
information field (encoded as subjectAltName / rfc822Name) and the
acp-domain-name in that peer's domain information field is the
same as in this ACP node's certificate.
The candidate peer certificate's ACP domain information field has
a non-empty acp-address field (either 32hex-dig or 0, according to
acp-dominfo-abnf).
Rule 6: for the establishment of ACP secure channels ensures that
they will only be built between nodes which indicate through the acp-
address in their ACP domain certificate the ability and permission by
the Registrar to participate in ACP secure-channels.
Nodes with an empty acp-address field can only use their ACP domain
certificate for non-ACP-secure channel authentication purposes.
The special value 0 in an ACP certificates acp-address field is used
for nodes that can and should determine their ACP address through
other mechanisms than learning it through their ACP domain
certificate.  These ACP nodes are permitted to establish ACP secure
channels.  Mechanisms for those nodes to determine their ACP address
are outside the scope of this specification.
ACP nodes MUST support certificate renewal via EST ("Enrollment over
Secure Transport", see RFC7030) and MAY support other mechanisms.  An
ACP network MUST have at least one ACP node supporting EST server
functionality across the ACP so that EST renewal is useable.
ACP nodes SHOULD be able to remember the EST server from which they
last renewed their ACP domain certificate and SHOULD provide the
ability for this remembered EST server to also be set by the ACP
Registrar (see acp-registrars) that initially enrolled the ACP device
with its ACP domain certificate.  When BRSKI (see I-D.ietf-anima-
bootstrapping-keyinfra) is used, the ACP address of the BRSKI
registrar from the BRSKI TLS connection SHOULD be remembered and used
for the next renewal via EST if that registrar also announces itself
as an EST server via GRASP (see next section) on its ACP address.
The objective value "SRV.est" indicates that the objective is an
RFC7030 compliant EST server because "est" is an RFC6335 registered
service name for RFC7030.  Objective-value MUST be ignored if
present.  Backward compatible extensions to RFC7030 MAY be indicated
through objective-value.  Non RFC7030 compatible certificate renewal
options MUST use a different objective-name.
The M_FLOOD message MUST be sent periodically.  The default SHOULD be
60 seconds, the value SHOULD be operator configurable but SHOULD be
not smaller than 60 seconds.  The frequency of sending MUST be such
that the aggregate amount of periodic M_FLOODs from all flooding
sources cause only negligible traffic across the ACP.  The time-to-
live (ttl) parameter SHOULD be 3.5 times the period so that up to
three consecutive messages can be dropped before considering an
announcement expired.  In the example above, the ttl is 210000 msec,
3.5 times 60 seconds.  When a service announcer using these
parameters unexpectedly dies immediately after sending the M_FLOOD,
receivers would consider it expired 210 seconds later.  When a
receiver tries to connect to this dead service before this timeout,
it will experience a failing connection and use that as an indication
that the service is dead and select another instance of the same
service instead.
When performing renewal, the node SHOULD attempt to connect to the
remembered EST server.  If that fails, it SHOULD attempt to connect
to an EST server learned via GRASP.  The server with which
certificate renewal succeeds SHOULD be remembered for the next
renewal.
Renewal of certificates SHOULD start after less than 50% of the
domain certificate lifetime so that network operations has ample time
to investigate and resolve any problems that causes a node to not
renew its domain certificate in time - and to allow prolonged periods
of running parts of a network disconnected from any CA.
The ACP node SHOULD support Certificate Revocation Lists (CRL) via
HTTPs from one or more CRL Distribution Points (CDPs).  The CDP(s)
MUST be indicated in the Domain Certificate when used.  If the CDP
URL uses an IPv6 address (ULA address when using the addressing rules
specified in this document), the ACP node will connect to the CDP via
the ACP.  If the CDP URL uses an IPv6 address (ULA address when using
the addressing rules specified in this document), the ACP node will
connect to the CDP via the ACP.  If the CDP uses a domain name, the
ACP node will connect to the CDP via the Data-Plane.
It is common to use domain names for CDP(s), but there is no
requirement for the ACP to support DNS.  Any DNS lookup in the Data-
Plane is not only a possible security issue, but it would also not
indicate whether the resolved address is meant to be reachable across
the ACP.  Therefore, the use of an IPv6 address versus the use of a
DNS name doubles as an indicator whether or not to reach the CDP via
the ACP.
Certificate lifetime may be set to shorter lifetimes than customary
(1 year) because certificate renewal is fully automated via ACP and
EST.  The primary limiting factor for shorter certificate lifetimes
is load on the EST server(s) and CA.  It is therefore recommended
that ACP domain certificates are managed via a CA chain where the
assigning CA has enough performance to manage short lived
certificates.  See also sub-ca for discussion about an example setup
achieving this.
When certificate lifetimes are sufficiently short, such as few hours,
certificate revocation may not be necessary, allowing to simplify the
overall certificate maintenance infrastructure.
An ACP node may determine that its ACP domain certificate has
expired, for example because the ACP node was powered down or
disconnected longer than its certificate lifetime.  In this case, the
ACP node SHOULD convert to a role of a re-enrolling candidate ACP
node.
In this role, the node does maintain the trust anchor and certificate
chain associated with its ACP domain certificate exclusively for the
purpose of re-enrollment, and attempts (or waits) to get re-enrolled
with a new ACP certificate.  The details depend on the mechanisms/
protocols used by the ACP registrars.
Please refer to acp-registrars for explanations about ACP registrars
and vouchers as used in the following text.
When BRSKI is used (aka: on ACP nodes that are ANI nodes), the re-
enrolling candidate ACP node would attempt to enroll like a candidate
ACP node (BRSKI pledge), but instead of using the ACP nodes IDevID,
it SHOULD first attempt to use its ACP domain certificate in the
BRSKI TLS authentication.  The BRSKI registrar MAY honor this
certificate beyond its expiration date purely for the purpose of re-
enrollment.  Using the ACP node's domain certificate allows the BRSKI
registrar to learn that nodes ACP domain information field, so that
the BRSKI registrar can re-assign the same ACP address information to
the ACP node in the new ACP domain certificate.
If the BRSKI registrar denies the use of the old ACP domain
certificate, the re-enrolling candidate ACP node MUST re-attempt re-
enrollment using its IDevID as defined in BRSKI during the TLS
connection setup.
Both when the BRSKI connection is attempted with the old ACP domain
certificate or the IDevID, the re-enrolling candidate ACP node SHOULD
authenticate the BRSKI registrar during TLS connection setup based on
its existing trust anchor/certificate chain information associated
with its old ACP certificate.  The re-enrolling candidate ACP node
SHOULD only request a voucher from the BRSKI registrar when this
authentication fails during TLS connection setup.
When other mechanisms than BRSKI are used for ACP domain certificate
enrollment, the principles of the re-enrolling candidate ACP node are
the same.  The re-enrolling candidate ACP node attempts to
authenticate any ACP registrar peers during re-enrollment protocol/
mechanisms via its existing certificate chain/trust anchor and
provides its existing ACP domain certificate and other identification
(such as the IDevID) as necessary to the registrar.
Maintaining existing trust anchor information is especially important
when enrollment mechanisms are used that unlike BRSKI do not leverage
a voucher mechanism to authenticate the ACP registrar and where
therefore the injection of certificate failures could otherwise make
the ACP node easily attackable remotely.
When using BRSKI or other protocol/mechanisms supporting vouchers,
maintaining existing trust anchor information allows for re-
enrollment of expired ACP certificates to be more lightweight,
especially in environments where repeated acquisition of vouchers
during the lifetime of ACP nodes may be operationally expensive or
otherwise undesirable.
An ACP domain certificate is called failing in this document, if/when
the ACP node can determine that it was revoked (or explicitly not
renewed), or in the absence of such explicit local diagnostics, when
the ACP node fails to connect to other ACP nodes in the same ACP
domain using its ACP certificate.  For connection failures to
determine the ACP domain certificate as the culprit, the peer should
pass the domain membership check (certcheck) and other reasons for
the connection failure can be excluded because of the connection
error diagnostics.
This type of failure can happen during setup/refresh of a secure ACP
channel connections or any other use of the ACP domain certificate,
such as for the TLS connection to an EST server for the renewal of
the ACP domain certificate.
Example reasons for failing certificates that the ACP node can only
discover through connection failure are that the domain certificate
or any of its signing certificates could have been revoked or may
have expired, but the ACP node cannot self-diagnose this condition
directly.  Revocation information or clock synchronization may only
be available across the ACP, but the ACP node cannot build ACP secure
channels because ACP peers reject the ACP node's domain certificate.
ACP nodes SHOULD support the option to determines whether its ACP
certificate is failing, and when it does, put itself into the role of
a re-enrolling candidate ACP node as explained above (domcert-re-
enroll).
To know to which nodes to establish an ACP channel, every ACP node
maintains an adjacency table.  The adjacency table contains
information about adjacent ACP nodes, at a minimum: Node-ID
(identifier of the node inside the ACP, see zone-scheme and Vlong),
interface on which neighbor was discovered (by GRASP as explained
below), link-local IPv6 address of neighbor on that interface,
certificate (including domain information field).  An ACP node MUST
maintain this adjacency table up to date.  This table is used to
determine to which neighbor an ACP connection is established.
Where the next ACP node is not directly adjacent (i.e., not on a link
connected to this node), the information in the adjacency table can
be supplemented by configuration.  For example, the Node-ID and IP
address could be configured.
Interaction between ACP and other autonomic elements like GRASP (see
below) or ASAs should be via an API that allows (appropriately access
controlled) read/write access to the ACP Adjacency Table.
Specification of such an API is subject to future work.
The ACP uses one instance of DULL GRASP ( See section 3.5.2.2 of I-
D.ietf-anima-grasp for its formal definition) for every physical L2
subnet of the ACP node to discover physically adjacent candidate ACP
neighbors.  Native interfaces (e.g.: physical interfaces on physical
nodes) SHOULD be brought up automatically enough so that ACP
discovery can be performed and any native interfaces with ACP
neighbors can then be brought into the ACP even if the interface is
otherwise not configured.  Reception of packets on such otherwise not
configured interfaces MUST be limited so that at first only IPv6
link-local address assignment (SLAAC) and DULL GRASP works and then
only the following ACP secure channel setup packets - but not any
other unnecessary traffic (e.g.: no other link-local IPv6 transport
stack responders for example).
Note that the use of the IPv6 link-local multicast address
(ALL_GRASP_NEIGHBORS) implies the need to use MLD (RFC3810) to
announce the desire to receive packets for that address.  Otherwise
DULL GRASP could fail to operate correctly in the presence of MLD
snooping, non-ACP enabled L2 switches - because those would stop
forwarding DULL GRASP packets.  Switches not supporting MLD snooping
simply need to operate as pure L2 bridges for IPv6 multicast packets
for DULL GRASP to work.
ACP discovery SHOULD NOT be enabled by default on non-native
interfaces.  In particular, ACP discovery MUST NOT run inside the ACP
across ACP virtual interfaces.  See enabling-acp for further, non-
normative suggestions how to enable/disable ACP at node and interface
level.  See conf-tunnel for more details about tunnels (typical non-
native interfaces).  See acp-l2-switches for how ACP should be
extended on devices operating (also) as L2 bridges.
Note: If an ACP node also implements BRSKI (see bootstrap) then the
above considerations also apply to discovery for BRSKI.  Each DULL
instance of GRASP set up for ACP is then also used for the discovery
of a bootstrap proxy via BRSKI when the node does not have a domain
certificate.  Discovery of ACP neighbors happens only when the node
does have the certificate.  The node therefore never needs to
discover both a bootstrap proxy and ACP neighbor at the same time.
DULL GRASP is a limited subset of GRASP intended to operate across an
insecure link-local scope.  See section 2.5.2 of I-D.ietf-anima-grasp
for its formal definition.  The ACP uses one instance of DULL GRASP
for every L2 interface of the ACP node to discover link level
adjacent candidate ACP neighbors.  Unless modified by policy as noted
earlier (overview bullet point 2.), native interfaces (e.g., physical
interfaces on physical nodes) SHOULD be initialized automatically to
a state in which ACP discovery can be performed and any native
interfaces with ACP neighbors can then be brought into the ACP even
if the interface is otherwise not configured.  Reception of packets
on such otherwise not configured interfaces MUST be limited so that
at first only IPv6 StateLess Address Auto Configuration (SLAAC -
RFC4862) and DULL GRASP work and then only the following ACP secure
channel setup packets - but not any other unnecessary traffic (e.g.,
no other link-local IPv6 transport stack responders for example).
Note that the use of the IPv6 link-local multicast address
(ALL_GRASP_NEIGHBORS) implies the need to use Multicast Listener
Discovery Version 2 (MLDv2, see RFC3810) to announce the desire to
receive packets for that address.  Otherwise DULL GRASP could fail to
operate correctly in the presence of MLD snooping, non-ACP enabled L2
switches - because those would stop forwarding DULL GRASP packets.
Switches not supporting MLD snooping simply need to operate as pure
L2 bridges for IPv6 multicast packets for DULL GRASP to work.
ACP discovery SHOULD NOT be enabled by default on non-native
interfaces.  In particular, ACP discovery MUST NOT run inside the ACP
across ACP virtual interfaces.  See enabling-acp for further, non-
normative suggestions on how to enable/disable ACP at node and
interface level.  See conf-tunnel for more details about tunnels
(typical non-native interfaces).  See acp-l2-switches for how ACP
should be extended on devices operating (also) as L2 bridges.
Note: If an ACP node also implements BRSKI to enroll its ACP domain
certificate (see bootstrap for a summary), then the above
considerations also apply to GRASP discovery for BRSKI.  Each DULL
instance of GRASP set up for ACP is then also used for the discovery
of a bootstrap proxy via BRSKI when the node does not have a domain
certificate.  Discovery of ACP neighbors happens only when the node
does have the certificate.  The node therefore never needs to
discover both a bootstrap proxy and ACP neighbor at the same time.
In the above (recommended) example the period of sending of the
objective could be 60 seconds the indicated ttl of 180000 msec means
that the objective would be cached by ACP nodes even when two out of
three messages are dropped in transit.
In the above example the RECOMMENDED period of sending of the
objective is 60 seconds.  The indicated ttl of 210000 msec means that
the objective would be cached by ACP nodes even when two out of three
messages are dropped in transit.
"IKEv2" is the abbreviation for "Internet Key Exchange protocol
version 2", as defined in RFC7296.  It is the main protocol used by
the Internet IP security architecture ("IPsec", see RFC4301).  We
therefore use the term "IKEv2" and not "IPsec" in the GRASP
definitions and example above.  "IKEv2" has a well-defined port
number 500, but in the above example, the candidate ACP neighbor is
offering ACP secure channel negotiation via IKEv2 on port 15000 (for
the sake of creating a non-standard example).
A node that supports more than one secure channel protocol method
needs to flood multiple versions of the "AN_ACP" objective so that
each method can be accompanied by its own locator-option.  This can
use a single GRASP M_FLOOD message as shown in above example.
"IKEv2" is the abbreviation for "Internet Key Exchange protocol
version 2", as defined in RFC7296.  It is the main protocol used by
the Internet IP security architecture (IPsec).  We therefore use the
term "IKEv2" and not "IPsec" in the GRASP definitions and example
above.  "IKEv2" has a well-defined port number 500, but in the above
example, the candidate ACP neighbor is offering ACP secure channel
negotiation via IKEv2 on port 15000 (for the sake of creating a non-
standard example).
"DTLS" indicates datagram Transport Layer Security version 1.2.
There is no default UDP port, it must always be locally assigned by
the node.  See DTLS.
A node that supports more than one secure channel protocol method
needs to flood multiple versions of the "AN_ACP" objective so that
each method can be accompanied by its own locator-option.  This can
use a single GRASP M_FLOOD message as shown in an-acp-example.
The ACP is by default established exclusively between nodes in the
same domain.  This includes all routing subdomains. domain-usage
explains how ACP connections across multiple routing subdomains are
special.
Build the ACP across all domains that have a common parent domain.
For example ACP nodes with domain "example.com", nodes of
"example.com", "access.example.com", "core.example.com" and
"city.core.example.com" could all establish one single ACP.
ACP connections across domains with different CA (certificate
authorities) could establish a common ACP by installing the
alternate domains' CA into the trusted anchor store.  This is an
executive management action that could easily be accomplished
through the control channel created by the ACP.
Since Intent is transported over the ACP, the first ACP connection a
node establishes is always following the default behavior.  See
domain-usage for more details.
The ACP is established exclusively between nodes in the same domain.
This includes all routing subdomains. domain-usage explains how ACP
connections across multiple routing subdomains are special.
From the use-cases it seems clear that not all type of ACP nodes can
or need to connect directly to each other or are able to support or
prefer all possible mechanisms.  For example, code space limited IoT
devices may only support dTLS ("datagram Transport Layer Security
version 1.2", see RFC6347) because that code exists already on them
for end-to-end security, but low-end in-ceiling L2 switches may only
want to support MacSec because that is also supported in their chips.
Only a flexible gateway device may need to support both of these
mechanisms and potentially more.
At this time in the lifecycle of ACP nodes, it is unclear whether it
is feasible to even decide on a single MTI (mandatory to implement)
security association protocol across all ACP nodes.
From the use-cases it seems clear that not all type of ACP nodes can
or need to connect directly to each other or are able to support or
prefer all possible mechanisms.  For example, code space limited IoT
devices may only support DTLS because that code exists already on
them for end-to-end security, but low-end in-ceiling L2 switches may
only want to support Media Access Control Security (MacSec, see
802.1AE (MACSEC) because that is also supported in their chips.  Only
a flexible gateway device may need to support both of these
mechanisms and potentially more.
An ACP node may choose to attempt initiate the different feasible ACP
secure channel protocols it supports according to its local policies
sequentially or in parallel, but it MUST support acting as a
responder to all of them in parallel.
Once the first secure channel protocol succeeds, the two peers know
each other's certificates because it must be used by all secure
channel protocols for mutual authentication.  The node with the lower
Node-ID in the ACP address becomes Bob, the one with the higher Node-
ID in the certificate Alice.
Bob becomes passive, he does not attempt to further initiate ACP
secure channel protocols with Alice and does not consider it to be an
error when Alice closes secure channels.  Alice becomes the active
party, continues to attempt setting up secure channel protocols with
Bob until she arrives at the best one from her view that also works
with Bob.
For example, originally Bob could have been the initiator of one ACP
secure channel protocol that Bob prefers and the security association
succeeded.  The roles of Bob and Alice are then assigned.  At this
stage, the protocol may not even have completed negotiating a common
security profile.  The protocol could for example could have been
IPsec via IKEv2 ("IP security", see RFC4301 and "Internet Key
Exchange protocol version 2", see RFC7296.  It is now up to Alice to
decide how to proceed.  Even if the IPsec connecting determined a
working profile with Bob, Alice might prefer some other secure
protocol (e.g.: dTLS) and try to set that up with Bob.  If that
succeeds, she would close the IPsec connection.  If no better
protocol attempt succeeds, she would keep the IPsec connection.
An ACP node may choose to attempt initiate the different feasible
ACP secure channel protocols it supports according to its local
policies sequentially or in parallel, but it MUST support acting
as a responder to all of them in parallel.
Once the first secure channel protocol succeeds, the two peers
know each other's certificates because they must be used by all
secure channel protocols for mutual authentication.  The node with
the lower Node-ID in the ACP address becomes Bob, the one with the
higher Node-ID in the certificate Alice.
Bob becomes passive, he does not attempt to further initiate ACP
secure channel protocols with Alice and does not consider it to be
an error when Alice closes secure channels.  Alice becomes the
active party, continues to attempt setting up secure channel
protocols with Bob until she arrives at the best one from her view
that also works with Bob.
For example, originally Bob could have been the initiator of one ACP
secure channel protocol that Bob prefers and the security association
succeeded.  The roles of Bob and Alice are then assigned.  At this
stage, the protocol may not even have completed negotiating a common
security profile.  The protocol could for example be IPsec via IKEv2
("IP security", see RFC4301 and "Internet Key Exchange protocol
version 2", see RFC7296.  It is now up to Alice to decide how to
proceed.  Even if the IPsec connection from Bob succeeded, Alice
might prefer another secure protocol over IPsec (e.g., FOOBAR), and
try to set that up with Bob.  If that preference of Alice succeeds,
she would close the IPsec connection.  If no better protocol attempt
succeeds, she would keep the IPsec connection.
Independent of the security association protocol chosen, candidate
ACP neighbors need to be authenticated based on their domain
certificate.  This implies that any secure channel protocol MUST
support certificate based authentication that can support the ACP
domain membership check as defined in certcheck.  If it fails, the
connection attempt is aborted and an error logged (with throttling).
Independent of the security association protocol chosen, candidate
ACP neighbors need to be authenticated based on their domain
certificate.  This implies that any secure channel protocol MUST
support certificate based authentication that can support the ACP
domain membership check as defined in certcheck.  If it fails, the
connection attempt is aborted and an error logged.  Attempts to
reconnect MUST be throttled.  The RECOMMENDED default is exponential
backoff with a minimum delay of 10 seconds and a maximum delay of 640
seconds.
To run ACP via IPsec natively, no further IANA assignments/
definitions are required.  An ACP node supporting native IPsec MUST
use IPsec security setup via IKEv2, tunnel mode, local and peer link-
local IPv6 addresses used for encapsulation.  It MUST support ESP
with AES256 for encryption and SHA256 hash and MUST NOT permit weaker
crypto options.
To run ACP via IPsec natively, no further IANA assignments/
definitions are required.  An ACP node that is supporting native
IPsec MUST use IPsec security setup via IKEv2, tunnel mode, local and
peer link-local IPv6 addresses used for encapsulation.  It MUST then
support ESP with AES256 for encryption and SHA256 hash and MUST NOT
permit weaker crypto options.
To run ACP via GRE/IPsec, no further IANA assignments/definitions are
required.  The ACP node MUST support IPsec security setup via IKEv2,
IPsec transport mode, local and peer link-local IPv6 addresses used
for encapsuation, ESP with AES256 encryption and SHA256 hash.
To run ACP via GRE/IPsec, no further IANA assignments/definitions are
required.  An ACP node that is supporting ACP via GRE/IPsec MUST then
support IPsec security setup via IKEv2, IPsec transport mode, local
and peer link-local IPv6 addresses used for encapsulation, ESP with
AES256 encryption and SHA256 hash.
A baseline ACP node MUST support IPsec natively and MAY support IPsec
via GRE.  A constrained ACP node MUST support dTLS.  ACP nodes
connecting constrained areas with baseline areas MUST therefore
support IPsec and dTLS.
ACP nodes need to specify in documentation the set of secure ACP
mechanisms they support.
As explained in the beginning of channel-selection, there is no
single secure channel mechanism mandated for all ACP nodes.  Instead,
this section defines two ACP profiles (baseline and constrained) for
ACP nodes that do introduce such requirements.
A baseline ACP node MUST support IPsec natively and MAY support IPsec
via GRE.  A constrained ACP node that cannot support IPsec MUST
support DTLS.  An ACP node connecting an area of constrained ACP
nodes with an area of baseline ACP nodes MUST therefore support IPsec
and DTLS and supports therefore the baseline and constrained profile.
ACP nodes need to specify in documentation the set of secure ACP
mechanisms they support and should declare which profile they support
according to above requirements.
The ACP MUST run an instance of GRASP inside of it.  It is a key part
of the ACP services.  They function in GRASP that makes it
fundamental as a service is the ability for ACP wide service
discovery (called objectives in GRASP).  In most other solution
designs such distributed discovery does not exist at all or was added
as an afterthought and relied upon inconsistently.
ACP provides IP unicast routing via the RPL routing protocol
(described below).
The ACP does not use IP multicast routing nor does it provide generic
IP multicast services (the handling of GRASP link-local multicast
messages is explained in the following section).  Instead, the ACP
provides service discovery via the objective discovery/announcement
and negotiation mechanisms of the ACP GRASP instance (services are a
form of objectives).  These mechanisms use hop-by-hop reliable
flooding of GRASP messages for both service discovery (GRASP
M_DISCOVERY messages) and service announcement (GRASP M_FLOOD
messages).
IP multicast is not used by the ACP because the ANI (Autonomic
Networking Infrastructure) itself does not require IP multicast but
only service announcement/discovery.  Using IP multicast for that
would have made it necessary to develop a zero-touch autoconfiguring
solution for ASM (Any Source Multicast - original form of IP
multicast defined in RFC1112), which would be quite complex and
difficult to justify.  One aspect of complexity that has never been
attempted to be solved in IETF documents is the automatic-selection
of routers that should be PIM-SM rendezvous points (RPs) (see
RFC7761).  The other aspects of complexity are the implementation of
MLD (RFC4604), PIM-SM and Anycast-RP (see RFC4610).  If those
implementations already exist in a product, then they would be very
likely tied to accelerated forwarding which consumes hardware
resources, and that in return is difficult to justify as a cost of
performing only service discovery.
Future ASA may need high performance in-network data replication.
That is the case when the use of IP multicast is justified.  These
ASA can then use service discovery from ACP GRASP, and then they do
not need ASM but only SSM (Source Specific Multicast, see RFC4607)
for the IP multicast replication.  SSM itself can simply be enabled
in the data-plane (or even in an update to the ACP) without any other
configuration than just enabling it on all nodes and only requires a
simpler version of MLD (see RFC5790).
LSP (Link State Protocol) based IGP routing protocols typically have
a mechanism to flood information, and such a mechanism could be used
to flood GRASP objectives by defining them to be information of that
IGP.  This would be a possible optimization in future variations of
the ACP that do use an LSP routing protocol.  Note though that such a
mechanism would not work easily for GRASP M_DISCOVERY messages which
are constrained flooded up to a node where a responder is found.  We
do expect that many future services in ASA will have only few
consuming ASA, and for those cases, M_DISCOVERY is the more efficient
method than flooding across the whole domain.
Because the ACP uses RPL, one desirable future extension is to use
RPLs existing notion of loop-free distribution trees (DODAG) to make
GRASPs flooding more efficient both for M_FLOOD and M_DISCOVERY) See
ACP_interfaces how this will be specifically beneficial when using
NBMA interfaces.  This is not currently specified in this document
because it is not quite clear yet what exactly the implications are
to make GRASP flooding depend on RPL DODAG convergence and how
difficult it would be to let GRASP flooding access the DODAG
information.
The ACP MUST run an instance of GRASP inside of it.  It is a key part
of the ACP services.  The function in GRASP that makes it fundamental
as a service of the ACP is the ability to provide ACP wide service
discovery (using objectives in GRASP).
ACP provides IP unicast routing via the RPL routing protocol (see
routing).
The ACP does not use IP multicast routing nor does it provide generic
IP multicast services (the handling of GRASP link-local multicast
messages is explained in GRASP-substrate).  Instead, the ACP provides
service discovery via the objective discovery/announcement and
negotiation mechanisms of the ACP GRASP instance (services are a form
of objectives).  These mechanisms use hop-by-hop reliable flooding of
GRASP messages for both service discovery (GRASP M_DISCOVERY
messages) and service announcement (GRASP M_FLOOD messages).
See acp-grasp for discussion about this design choice of the ACP.
This means that the ACP is responsible to ensure that this instance
of GRASP is only sending messages across the ACP GRASP virtual
interfaces.  Whenever the ACP adds or deletes such an interface
because of new ACP secure channels or loss thereof, the ACP needs to
indicate this to the ACP instance of GRASP.  The ACP exists also in
the absence of any active ACP neighbors.  It is created when the node
has a domain certificate, and continues to exist even if all of its
neighbors cease operation.
In this case ASAs using GRASP running on the same node would still
need to be able to discover each other's objectives.  When the ACP
does not exist, ASAs leveraging the ACP instance of GRASP via APIs
MUST still be able to operate, and MUST be able to understand that
there is no ACP and that therefore the ACP instance of GRASP can not
operate.
This means that the ACP is responsible for ensuring that this
instance of GRASP is only sending messages across the ACP GRASP
virtual interfaces.  Whenever the ACP adds or deletes such an
interface because of new ACP secure channels or loss thereof, the ACP
needs to indicate this to the ACP instance of GRASP.  The ACP exists
also in the absence of any active ACP neighbors.  It is created when
the node has a domain certificate, and continues to exist even if all
of its neighbors cease operation.
In this case ASAs using GRASP running on the same node would still
need to be able to discover each other's objectives.  When the ACP
does not exist, ASAs leveraging the ACP instance of GRASP via APIs
MUST still be able to operate, and MUST be able to understand that
there is no ACP and that therefore the ACP instance of GRASP cannot
operate.
TLS and TLS connections for GRASP in the ACP use the IANA assigned
TCP port for GRASP (7107).  Effectively the transport stack is
expected to be TLS for connections from/to the ACP address (e.g.:
global scope address(es)) and TCP for connections from/to link-local
addresses on the ACP virtual interfaces.  The latter ones are only
used for flooding of GRASP messages.
TLS and TLS connections for GRASP in the ACP use the IANA assigned
TCP port for GRASP (7107).  Effectively the transport stack is
expected to be TLS for connections from/to the ACP address (e.g.,
global scope address(es)) and TCP for connections from/to link-local
addresses on the ACP virtual interfaces.  The latter ones are only
used for flooding of GRASP messages.
TCP encapsulation for GRASP M_DISCOVERY and M_FLOOD link local
messages is used because these messages are flooded across
potentially many hops to all ACP nodes and a single link with even
temporary packet loss issues (e.g.: WiFi/Powerline link) can reduce
the probability for loss free transmission so much that applications
would want to increase the frequency with which they send these
messages.  This would result in more traffic flooding than hop-by-hop
reliable retransmission as provided for by TCP.
TLS is mandated for GRASP non-link-local unicast because the ACP
secure channel mandatory authentication and encryption protects only
against attacks from the outside but not against attacks from the
inside: Compromised ACP members that have (not yet) been detected and
removed (e.g.: via domain certificate revocation / expiry).
TCP encapsulation for GRASP M_DISCOVERY and M_FLOOD link local
messages is used because these messages are flooded across
potentially many hops to all ACP nodes and a single link with even
temporary packet loss issues (e.g., WiFi/Powerline link) can reduce
the probability for loss free transmission so much that applications
would want to increase the frequency with which they send these
messages.  Such shorter periodic retransmission of datagrams would
result in more traffic and processing overhead in the ACP than the
hop-by-hop reliable retransmission mechanism by TCP and duplicate
elimination by GRASP.
TLS is mandated for GRASP non-link-local unicast because the ACP
secure channel mandatory authentication and encryption protects only
against attacks from the outside but not against attacks from the
inside: Compromised ACP members that have (not yet) been detected and
removed (e.g., via domain certificate revocation / expiry).
Eavesdropping/spoofing by a compromised ACP node is still possible
because in the model of the ACP and GRASP, the provider and consumer
of an objective have initially no unique information (such as an
identity) about the other side which would allow them to distinguish
a benevolent from a compromised peer.  The compromised ACP node would
simply announce the objective as well, potentially filter the
original objective in GRASP when it is a MITM and act as an
application level proxy.  This of course requires that the
compromised ACP node understand the semantic of the GRASP negotiation
to an extend that allows it to proxy it without being detected, but
in an AN environment this is quite likely public knowledge or evens
standardized.
The security considerations for GRASP change against attacks from
non-ACP (e.g.: "outside") nodes: TLS is subject to reset attacks
while secure channel protocols may be not (e.g.: IPsec is not).
The GRASP TLS connections need to implement any additional
security options that are required for secure channels.  For
example the closing of connections when the peers certificate has
expired.
The ACP is in a separate context from the normal data-plane of the
node.  This context includes the ACP channels IPv6 forwarding and
routing as well as any required higher layer ACP functions.
In classical network systems, a dedicated so called "Virtual routing
and forwarding instance" (VRF) is one logical implementation option
for the ACP.  If possible by the systems software architecture,
separation options that minimize shared components are preferred,
such as a logical container or virtual machine instance.  The context
for the ACP needs to be established automatically during bootstrap of
a node.  As much as possible it should be protected from being
modified unintentionally by ("data-plane") configuration.
Context separation improves security, because the ACP is not
reachable from the global routing table.  Also, configuration errors
from the data-plane setup do not affect the ACP.
Eavesdropping/spoofing by a compromised ACP node is still possible
because in the model of the ACP and GRASP, the provider and consumer
of an objective have initially no unique information (such as an
identity) about the other side which would allow them to distinguish
a benevolent from a compromised peer.  The compromised ACP node would
simply announce the objective as well, potentially filter the
original objective in GRASP when it is a MITM and act as an
application level proxy.  This of course requires that the
compromised ACP node understand the semantics of the GRASP
negotiation to an extent that allows it to proxy it without being
detected, but in an ACP environment this is quite likely public
knowledge or even standardized.
Secure channel methods such as IPsec may provide protection
against additional attacks, for example reset-attacks.
There is no different security model for ACP GRASP from other ACP
traffic.  Instead, there is just another layer of protection
against certain attacks from the inside which is important due to
the role of GRASP in the ACP.
The ACP is in a separate context from the normal Data-Plane of the
node.  This context includes the ACP channels' IPv6 forwarding and
routing as well as any required higher layer ACP functions.
In classical network system, a dedicated so called Virtual routing
and forwarding instance (VRF) is one logical implementation option
for the ACP.  If possible by the systems software architecture,
separation options that minimize shared components are preferred,
such as a logical container or virtual machine instance.  The context
for the ACP needs to be established automatically during bootstrap of
a node.  As much as possible it should be protected from being
modified unintentionally by ("Data-Plane") configuration.
Context separation improves security, because the ACP is not
reachable from the Data-Plane routing or forwarding table(s).  Also,
configuration errors from the Data-Plane setup do not affect the ACP.
With the algorithm introduced here, all ACP nodes in the same routing
subdomain have the same /48 ULA global ID prefix.  Conversely, ULA
global IDs from different domains are unlikely to clash, such that
two networks can be merged, as long as the policy allows that merge.
See also self-healing for a discussion on merging domains.
With the algorithm introduced here, all ACP nodes in the same routing
subdomain have the same /48 ULA prefix.  Conversely, ULA global IDs
from different domains are unlikely to clash, such that two ACP
networks can be merged, as long as the policy allows that merge.  See
also self-healing for a discussion on merging domains.
Use-ULA: For loopback interfaces of ACP nodes, we use Unique Local
Addresses (ULA), specifically ULA-Random, as defined in [RFC4193
with L=1].
Use-ULA: For Loopback interfaces of ACP nodes, we use Unique Local
Addresses (ULA), as defined in RFC4193 with L=1 (as defined in
section 3.1 of RFC4193).  Note that the random hash for ACP
Loopback addresses uses the definition in scheme and not the one
of RFC4193 section 3.2.2.
OAM protocols no not require IPv4: The ACP may carry OAM
protocols.  All relevant protocols (SNMP, TFTP, SSH, SCP, Radius,
Diameter, ...) are available in IPv6.
The 40 bits ULA "global ID" (term from RFC4193) for ACP addresses
carried in the domain information field of domain certificates are
the first 40 bits of the SHA256 hash of the routing subdomain from
the same domain information field.  In the example of domcert-
acpinfo, the routing subdomain is
"area51.research.acp.example.com" and the 40 bits ULA "global ID"
89b714f3db.
To allow for extensibility, the fact that the ULA "global ID" is a
hash of the routing subdomain SHOULD NOT be assumed by any ACP
node during normal operations.  The hash function is only executed
during the creation of the certificate.  If BRSKI is used then the
registrar will create the domain information field in response to
the CSR Attribute Request by the pledge.
OAM protocols do not require IPv4: The ACP may carry OAM
protocols.  All relevant protocols (SNMP, TFTP, SSH, SCP, Radius,
Diameter, ...) are available in IPv6.  See also RFC8368 for how
ACP could be made to interoperate with IPv4 only OAM.
The 40-bits ULA "global ID" (term from RFC4193) for ACP addresses
carried in the domain information field of domain certificates are
the first 40-bits of the SHA256 hash of the routing subdomain from
the same domain information field.  In the example of domcert-
acpinfo, the routing subdomain is
"area51.research.acp.example.com" and the 40-bits ULA "global ID"
89b714f3db.
To allow for extensibility, the fact that the ULA "global ID" is a
hash of the routing subdomain SHOULD NOT be assumed by any ACP
node during normal operations.  The hash function is only executed
during the creation of the certificate.  If BRSKI is used then the
BRSKI registrar will create the domain information field in
response to the EST Certificate Signing Request (CSR) Attribute
Request message by the pledge.
Please refer to acp-registrars and address-spaces for further
explanations why the following Sub-Addressing schemes are used and
why multiple are necessary.
The sub-scheme defined here is defined by the Type value 00b (zero)
in the base scheme and 0 in the Z bit.
Registrar-ID (48 bit): A number unique inside the domain that
identifies the registrar which assigned the Node-ID to the node.
A MAC address of the registrar can be used for this purpose.
Node-Number: A number which is unique for a given registrar, to
identify the node.  This can be a sequentially assigned number.
V (1 bit): Virtualization bit: 0: Indicates the ACP itself ("ACP
node base system); 1: Indicates the optional "host" context on the
ACP node (see below).
Registrar-ID (48-bit): A number unique inside the domain that
identifies the ACP registrar which assigned the Node-ID to the
node.  A MAC address of the ACP registrar can be used for this
purpose.
Node-Number: A number which is unique for a given ACP registrar,
to identify the node.  This can be a sequentially assigned number.
V (1-bit): Virtualization bit: 0: Indicates the ACP itself ("ACP
node base system); 1: Indicates the optional "host" context on the
ACP node (see below).
The Virtual bit in this sub-scheme allows to easily add the ACP as a
component to existing systems without causing problems in the port
number space between the services in the ACP and the existing system.
V:0 is the ACP router (autonomic node base system), V:1 is the host
with pre-existing transport endpoints on it that could collide with
the transport endpoints used by the ACP router.  The ACP host could
for example have a p2p virtual interface with the V:0 address as its
router into the ACP.  Depending on the SW design of ASA (outside the
scope of this specification), they may use the V:0 or V:1 address.
The location of the V bit(s) at the end of the address allows to
announce a single prefix for each ACP node.  For example, in a
network with 20,000 ACP nodes, this avoid 20,000 additional routes in
the routing table.
The Zone-ID allows for the introduction of structure in the
addressing scheme.
The Virtual bit in this sub-scheme allows the easy addition of the
ACP as a component to existing systems without causing problems in
the port number space between the services in the ACP and the
existing system.  V:0 is the ACP router (autonomic node base system),
V:1 is the host with pre-existing transport endpoints on it that
could collide with the transport endpoints used by the ACP router.
The ACP host could for example have a p2p virtual interface with the
V:0 address as its router into the ACP.  Depending on the software
design of ASAs, which is outside the scope of this specification,
they may use the V:0 or V:1 address.
The location of the V bit(s) at the end of the address allows the
announcement of a single prefix for each ACP node.  For example, in a
network with 20,000 ACP nodes, this avoid 20,000 additional routes in
the routing table.
The Zone-ID allows for the introduction of route prefixes in the
addressing scheme.
If aggregation is required, the 13 bit Zone-ID value allows for up to
8191 zones.  The allocation of Zone-ID's may either happen
automatically through a to-be-defined algorithm; or it could be
configured and maintained explicitly.
If a node learns through a future autonomic method or through
configuration that it is part of a zone, it MUST also respond to its
ACP address with that Zone-ID.  In this case the ACP loopback is
configured with two ACP addresses: One for Zone-ID = 0 and one for
the assigned Zone-ID.  This method allows for a smooth transition
between a flat addressing scheme and an hierarchical one.
A node knowing it is in a zone MUST also use that Zone-ID != 0
address in GRASP locator fields.  This eliminates the use of the
identifier address (Zone-ID = 0) in forwarding and the need for
network wide reachability of those non-aggregateable identifier
addresses.  Zone-ID != 0 addresses are assumed to be aggregateable in
routing/forwarding based on how they are allocated in the ACP
topology (subject to future work).
Note: Theoretically, the 13 bits for the Zone-ID would allow also for
two levels of zones, introducing a sub-hierarchy.  We do not think
this is required at this point, but a new type could be used in the
future to support such a scheme.
Note: The Zone-ID is one method to introduce structure or hierarchy
into the ACP.  Another way is the use of the routing subdomain field
in the ACP that leads to different /40 ULA prefixes within an ACP
domain.  This gives future work two options to consider.
If aggregation is required, the 13-bit Zone-ID value allows for up to
8191 zones.  The allocation of Zone-ID's may either happen
automatically through a to-be-defined algorithm; or it could be
configured and maintained explicitly.
If a node learns (see auto-aggregation) that it is part of a zone, it
MUST also respond to its ACP address with that Zone-ID.  In this case
the ACP Loopback is configured with two ACP addresses: One for Zone-
ID = 0 and one for the assigned Zone-ID.  This method allows for a
smooth transition between a flat addressing scheme and a hierarchical
one.
A node knowing it is in a zone MUST also use that Zone-ID != 0
address in GRASP locator fields.  This eliminates the use of the
identifier address (Zone-ID = 0) in forwarding and the need for
network wide reachability of those non-aggregable identifier
addresses.  Zone-ID != 0 addresses are assumed to be aggregable in
routing/forwarding based on how they are allocated in the ACP
topology.
Note: The Zone-ID is one method to introduce structure or hierarchy
into the ACP.  Another way is the use of the routing subdomain field
in the ACP that leads to multiple /48 Global IDs within an ACP
domain.
The sub-scheme defined here is defined by the Type value 00b (zero)
in the base scheme and 1 in the Z bit.
"Manual" means that allocations of the Subnet-ID need to be done
today with pre-existing, non-autonomic mechanisms.  Every subnet that
uses this addressing sub-scheme needs to use a unique Subnet-ID
(unless some anycast setup is done).  Future work may define
mechanisms for auto-coordination between ACP nodes and auto-
allocation of Subnet-IDs between them.
The Z field is following the Subnet-ID field so that future work
could allocate/coordinate both Zone-ID and Subnet-ID consistently and
use an integrated aggregatable routing approach across them.  Z=0
(Zone-ID sub-scheme) would then be used for network wide unique,
registrar assigned (and certificate protected) Node-IDs primarily for
ACP nodes while Z=1 would be used for node-level assigned Interface
Identifiers primarily for non-ACP-nodes (on logical subnets where the
ACP node is a router).
Manual addressing sub-scheme addresses SHOULD only be used in domain
certificates assigned to nodes that cannot fully participate in the
automatic establishment of ACP secure channels or ACP routing.  The
intended use are nodes connecting to the ACP via an ACP edge node and
ACP connect (see ACPconnect) - such as legacy NOC equipment.  They
would not use their domain certificate for ACP secure channel
creation and therefore do not need to participate in ACP routing
either.  They would use the certificate for authentication of any
transport services.  The value of the Interface Identifier is left
for future definitions.
"Manual" means that allocations of the Subnet-ID need to be done
today with pre-existing, non-autonomic mechanisms.  Every subnet that
uses this addressing sub-scheme needs to use a unique Subnet-ID
(unless some anycast setup is done).
The Z bit field was added to distinguish Zone addressing and manual
addressing sub-schemes without requiring one more bit in the base
scheme and therefore allowing for the Vlong scheme (described below)
to have one more bit available.
Manual addressing sub-scheme addresses SHOULD NOT be used in ACP
domain certificates.  Any node capable to build ACP secure channels
and permitted by Registrar policy to participate in building ACP
secure channels SHOULD receive an ACP address (prefix) from one of
the other ACP addressing sub-schemes.  Nodes not capable (or
permitted) to participate in ACP secure channels can connect to the
ACP via ACP connect interfaces of ACP edge nodes (see ACPconnect),
without setting up an ACP secure channel.  Their ACP domain
certificate MUST include an empty acp-address to indicate that their
ACP domain certificate is only usable for non- ACP secure channel
authentication, such as end-to-end transport connections across the
ACP or Data-Plane.
Address management of ACP connect subnets is done using traditional
assignment methods and existing IPv6 protocols.  See ACautoconfig for
details.
This addressing scheme foregoes the Zone-ID field to allow for
larger, flatter routed networks (e.g.: as in IoT) with 8421376 Node-
Numbers (2^23+2^15).  It also allows for up to 2^16 - 65536 different
virtualized addresses within a node, which could be used to address
individual software components in an ACP node.
V: Virtualization bit: Values 0 and 1 as in Zone-ID sub-scheme,
further values use via definition in future work.
Registrar-ID: To maximize Node-Number and V, the Registrar-ID is
reduced to 46 bits.  This still allows to use the MAC address of a
registrar by removing the V and U bits from the 48 bits of a MAC
address (those two bits are never unique, so they cannot be used
to distinguish MAC addresses).
If the first bit of the "Node-Number" is "1", then the Node-Number
is 16 bit long and the V field is 16 bit long.  Otherwise the
Node-Number is 24 bit long and the V field is 8 bit long.  "0" bit
Node-Numbers are intended to be used for "general purpose" ACP
nodes that would potentially have a limited number (< 256) of
clients (ASA/Autonomic Functions or legacy services) of the ACP
that require separate V(irtual) addresses.  "1" bit Node-Numbers
are intended for ACP nodes that are ACP edge nodes (see NMS) or
that have a large number of clients requiring separate V(irtual)
addresses.  For example large SDN controllers with container
modular software architecture (see software).
This addressing scheme foregoes the Zone-ID field to allow for
larger, flatter routed networks (e.g., as in IoT) with 8421376 Node-
Numbers (2^23+2^15).  It also allows for up to 2^16 (i.e. 65536)
different virtualized addresses within a node, which could be used to
address individual software components in an ACP node.
F: format bit.  This bit determines the format of the subsequent
bits.
V: Virtualization bit: this is a field that is either 8 or 16
bits.  For F=0, it is 8 bits, for F=1 it is 16 bits.  The V bits
are assigned by the ACP node.  In the certificate domcert-acpinfo,
the V-bits are always set to 0.
Registrar-ID: To maximize Node-Number and V, the Registrar-ID is
reduced to 46-bits.  This still permits the use of the MAC address
of an ACP registrar by removing the V and U bits from the 48-bits
of a MAC address (those two bits are never unique, so they cannot
be used to distinguish MAC addresses).
The Node-Number is unique to each ACP node.  There are two formats
for the Node-Number.  When F=0, the node-number is 23 bits, for
F=1 it is 15 bits.  Each format of node-number is considered to be
in a unique number space.
The F=0 bit format addresses are intended to be used for "general
purpose" ACP nodes that would potentially have a limited number (<
256) of clients (ASA/Autonomic Functions or legacy services) of the
ACP that require separate V(irtual) addresses.
The F=1 bit Node-Numbers are intended for ACP nodes that are ACP edge
nodes (see NMS) or that have a large number of clients requiring
separate V(irtual) addresses.  For example large SDN controllers with
container modular software architecture (see software).
Before further addressing sub-schemes are defined, experience with
the schemes defined here should be collected.  The schemes defined in
this document have been devised to allow hopefully sufficiently
flexible setup of ACPs for a variety of situation.  These reasons
also lead to the fairly liberal use of address space: The Zone
Addressing Sub-Scheme is intended to enable optimized routing in
large networks by reserving bits for Zone-ID's.  The Vlong addressing
sub-scheme enables the allocation of 8/16 bit of addresses inside
individual ACP nodes.  Both address spaces allow distributed,
uncoordinated allocation of node addresses by reserving bits for the
Registrar-ID field in the address.
IANA is asked need to assign a new "type" for each new addressing
sub-scheme.  With the current allocations, only 2 more schemes are
possible, so the last addressing scheme should consider to be
extensible in itself (e.g.: by reserving bits from it for further
extensions.
Before further addressing sub-schemes are defined, experience with
the schemes defined here should be collected.  The schemes defined in
this document have been devised to allow hopefully sufficiently
flexible setup of ACPs for a variety of situation.  These reasons
also lead to the fairly liberal use of address space: The Zone
Addressing Sub-Scheme is intended to enable optimized routing in
large networks by reserving bits for Zone-ID's.  The Vlong addressing
sub-scheme enables the allocation of 8/16-bit of addresses inside
individual ACP nodes.  Both address spaces allow distributed,
uncoordinated allocation of node addresses by reserving bits for the
registrar-ID field in the address.
IANA is asked need to assign a new "type" for each new addressing
sub-scheme.  With the current allocations, only 2 more schemes are
possible, so the last addressing scheme MUST provide further
extensions (e.g., by reserving bits from it for further extensions).
The ACP address prefix is assigned to the ACP node during enrollment/
provisioning of the ACP domain certificate to the ACP node.  It is
intended to persist unchanged through the lifetime of the ACP node.
Because of the ACP addressing sub-schemes explained above, ACP nodes
for a single ACP domain can be enrolled by multiple distributed and
uncoordinated entities called ACP registrars.  These ACP registrars
are responsible to enroll ACP domain certificates and associated
trust anchor(s) to candidate ACP nodes and are also responsible that
an ACP domain information field is included in the ACP domain
certificate.
Any protocols or mechanisms may be used as ACP registrars, as long as
the resulting ACP certificate and trust anchors allow to perform the
ACP domain membership described in certcheck with other ACP domain
members, and meet the ACP addressing requirements for its ACP domain
information field as described further below in this section.
An ACP registrar could be a person deciding whether to enroll a
candidate ACP node and then orchestrating the enrollment of the ACP
certificate and associated trust anchor, using command line or web
based commands on the candidate ACP node and trust anchor to generate
and sign the ACP domain certificate and configure certificate and
trust anchors onto the node.
The only currently defined protocol for ACP registrars is BRSKI (I-
D.ietf-anima-bootstrapping-keyinfra).  When BRSKI is used, the ACP
nodes are called ANI nodes, and the ACP registrars are called BRSKI
or ANI registrars.  The BRSKI specification does not define the
handling of the ACP domain information field because the rules do not
depend on BRSKI but apply equally to any protocols/mechanisms an ACP
registrar may use.
ACP registrars MUST NOT allocate ACP address prefixes to ACP nodes
via the ACP domain information field that would collide with the ACP
address prefixes of other ACP nodes in the same ACP domain.  This
includes both prefixes allocated by the same ACP registrar to
different ACP nodes as well as prefixes allocated by other ACP
registrars for the same ACP domain.
For this purpose, an ACP registrar MUST have one or more unique
46-bit identifiers called Registrar-IDs used to allocate ACP address
prefixes.  The lower 46-bits of a EUI-48 MAC addresses are globally
unique 46 bit identifiers, so ACP registrars with known unique EUI-48
MAC addresses can use these as Registrar-IDs.  Registrar-IDs do not
need to be globally unique but only unique across the set of ACP
registrars for an ACP domain, so other means to assign unique
Registrar-IDs to ACP registrars can be used, such as configuration on
the ACP registrars.
When the candidate ACP device (called Pledge in BRSKI) is to be
enrolled into an ACP domain, the ACP registrar needs to allocate a
unique ACP address to the node and ensure that the ACP certificate
gets a domain information field (domcert-acpinfo) with the
appropriate information - ACP domain-name, ACP-address, and so on.
If the ACP registrar uses BRSKI, it signals the ACP information field
to the Pledge via the EST /csraddrs command (see I-D.ietf-anima-
bootstrapping-keyinfra, section 5.8.2 - "EST CSR Attributes").
The ACP registrar selects for the candidate ACP node a unique address
prefix from an appropriate ACP addressing sub-scheme, either a zone
addressing sub-scheme prefix (see zone-scheme), or a Vlong addressing
sub-scheme prefix (see Vlong).  The assigned ACP address prefix
encoded in the domain information field of the ACP domain certificate
indicates to the ACP node its ACP address information.  The sub-
addressing scheme indicates the prefix length: /127 for zone address
sub-scheme, /120 or /112 for Vlong address sub-scheme.  The first
address of the prefix is the ACP address, all other addresses in the
prefix are for other uses by the ACP node as described in the zone
and Vlong addressing sub scheme sections.  The ACP address prefix
itself is then signaled by the ACP node into the ACP routing protocol
(see routing) to establish IPv6 reachability across the ACP.
The choice of addressing sub-scheme and prefix-length in the Vlong
address sub-scheme is subject to ACP registrar policy.  It could be
an ACP domain wide policy, or a per ACP node or per ACP node type
policy.  For example, in BRSKI, the ACP registrar is aware of the
IDevID of the candidate ACP node, which contains a serialNnumber that
is typically indicating the nodes vendor and device type and can be
used to drive a policy selecting an appropriate addressing sub-scheme
for the (class of) node(s).
ACP registrars SHOULD default to allocate ACP zone sub-address scheme
addresses with Subnet-ID 0.  Allocation and use of zone sub-addresses
with Subnet-ID != 0 is outside the scope of this specification
because it would need to go along with rules for extending ACP
routing to multiple zones, which is outside the scope of this
specification.
ACP registrars that can use the IDevID of a candidate ACP device
SHOULD be able to choose the zone vs. Vlong sub-address scheme for
ACP nodes based on the serialNumber of the IDevID, for example by the
PID (Product Identifier) part which identifies the product type, or
the complete serialNumber.
In a simple allocation scheme, an ACP registrar remembers
persistently across reboots for its currently used Registrar-ID and
for each addressing scheme (zone with Subnet-ID 0, Vlong with /112,
Vlong with /120), the next Node-Number available for allocation and
increases it after successful enrollment to an ACP node.  In this
simple allocation scheme, the ACP registrar would not recycle ACP
address prefixes from no longer used ACP nodes.
When an ACP domain certificate is renewed or rekeyed via EST or other
mechanisms, the ACP address/prefix in the ACP domain information
field MUST be maintained unless security issues or violations of the
unique address assignment requirements exist or are suspected by the
ACP registrar.  Even when the renewing/rekeying ACP registrar is not
the same as the one that enrolled the prior ACP certificate.  See
sub-ca for an example.  ACP address information SHOULD also be
maintained even after an ACP certificate did expire or failed.  See
domcert-re-enroll and domcert-failing.
registrar-considerations discusses further informative details of ACP
registrars: What interactions registrars need, what parameters they
require, certificate renewal and limitations, use of sub-CAs on
registrars and centralized policy control.
Once ULA address are set up all autonomic entities should run a
routing protocol within the autonomic control plane context.  This
routing protocol distributes the ULA created in the previous section
for reachability.  The use of the autonomic control plane specific
context eliminates the probable clash with the global routing table
and also secures the ACP from interference from the configuration
mismatch or incorrect routing updates.
Once ULA address are set up all autonomic entities should run a
routing protocol within the autonomic control plane context.  This
routing protocol distributes the ULA created in the previous section
for reachability.  The use of the autonomic control plane specific
context eliminates the probable clash with Data-Plane routing tables
and also secures the ACP from interference from the configuration
mismatch or incorrect routing updates.
In summary, the profile chosen for RPL is one that expects a fairly
reliable network reasonable fast links so that RPL convergence will
be triggered immediately upon recognition of link failure/recovery.
The key limitation of the chosen profile is that it is designed to
not require any data-plane artifacts (such as RFC6553).  While the
senders/receivers of ACP packets can be legacy NOC devices connected
via "ACP connect" (see NMS to the ACP, their connectivity can be
handled as non-RPL-aware leafs (or "Internet") according to the data-
plane architecture explained in I-D.ietf-roll-useofrplinfo.  This
non-artifact profile is largely driven by the desire to avoid
introducing the required Hop-by-Hop headers into the ACP VRF control
plane.  Many devices will have their VRF forwarding code designed
into silicon.
In this profile choice, RPL has no data-plane artifacts.  A simple
destination prefix based upon the routing table is used.  A
consequence of supporting only a single instanceID (containing one
DODAG), the ACP will only accommodate only a single class of routing
table and cannot create optimized routing paths to accomplish latency
or energy goals.
Consider a network that has multiple NOCs in different locations.
Only one NOC will become the DODAG root.  Other NOCs will have to
send traffic through the DODAG (tree) rooted in the primary NOC.
Depending on topology, this can be an annoyance from a latency point
of view, but it does not represent a single point of failure, as the
DODAG can reconfigure itself when it detects data plane forwarding
failures.
The lack of a RPI (the header defined by RFC6553), means that the
data-plane will have no rank value that can be used to detect loops.
As a result, traffic may loop until the TTL of the packet reaches
zero.  This the same behavior as that of other IGPs that do not have
the data-plane options as RPPL.  There are a variety of heuristics
that can be used to signal from the data-plane to the RPL control
plane that a new route is needed.
Additionally, failed ACP tunnels will be detected by IKEv2 Dead Peer
Detection (which can function as a replacement for an LLN's ETX).  A
failure of an ACP tunnel should signal the RPL control plane to pick
a different parent.
Future Extensions to this RPL profile can provide optimality for
multiple NOCs.  This requires utilizing data-plane artifact including
IPinIP encap/decap on ACP routers and processing of IPv6 RPI headers.
Alternatively, (Src,Dst) routing table entries could be used.  A
decision for the preferred technology would have to be done when such
extension is defined.
In summary, the profile chosen for RPL is one that expects a fairly
reliable network with reasonably fast links so that RPL convergence
will be triggered immediately upon recognition of link failure/
recovery.
The key limitation of the chosen profile is that it is designed to
not require any Data-Plane artifacts (such as RFC6553).  While the
senders/receivers of ACP packets can be legacy NOC devices connected
via ACP connect (see NMS to the ACP, their connectivity can be
handled as non-RPL-aware leafs (or "Internet") according to the Data-
Plane architecture explained in I-D.ietf-roll-useofrplinfo.  This
non-artifact profile is largely driven by the desire to avoid
introducing the required Hop-by-Hop headers into the ACP forwarding
plane, especially to support devices with silicon forwarding planes
that cannot support insertion/removal of these headers in silicon.
In this profile choice, RPL has no Data-Plane artifacts.  A simple
destination prefix based upon the routing table is used.  A
consequence of supporting only a single instanceID that is containing
one Destination Oriented Directed Acyclic Graph (DODAG), the ACP will
only accommodate only a single class of routing table and cannot
create optimized routing paths to accomplish latency or energy goals.
Consider a network that has multiple NOCs in different locations.
Only one NOC will become the DODAG root.  Other NOCs will have to
send traffic through the DODAG (tree) rooted in the primary NOC.
Depending on topology, this can be an annoyance from a latency point
of view, but it does not represent a single point of failure, as the
DODAG will reconfigure itself when it detects data plane forwarding
failures.  See future-rpl for more details.
The lack of RPL Packet Information (RPI, the IPv6 header for RPL
defined by RFC6553), means that the Data-Plane will have no rank
value that can be used to detect loops.  As a result, traffic may
loop until the time-to-live (TTL) of the packet reaches zero.  This
the same behavior as that of other IGPs that do not have the Data-
Plane options as RPL.
Since links in the ACP are assumed to be mostly reliable (or have
link layer protection against loss) and because there is no stretch
according to rpl-dodag-repair, loops should be exceedingly rare
though.
There are a variety of mechanisms possible in RPL to further avoid
temporary loops: DODAG Information Objects (DIOs) SHOULD be sent
technique in RFC6550 section 8.2.2.6.  (Detaching) SHOULD be favored
over that in section 8.2.2.5., (Poisoning) because it allows local
connectivity.  Nodes SHOULD select more than one parent, at least 3
if possible, and send Destination Advertisement Objects (DAO)s to all
of them in parallel.
Additionally, failed ACP tunnels will be detected by IKEv2 Dead Peer
Detection (which can function as a replacement for a Low-power and
Lossy Networks' (LLN's) Expected Transmission Count (ETX).  A failure
of an ACP tunnel should signal the RPL control plane to pick a
different parent.
RPL Mode of Operations (MOP): mode 3 "Storing Mode of Operations with
multicast support".  Implementations should support also other modes.
Note: Root indicates mode in DIO flow.
RPL Mode of Operations (MOP): MUST support mode 2 - "Storing Mode of
Operations with no multicast support".  Implementations MAY support
mode 3 ("... with multicast support" as that is a superset of mode
2).  Note: Root indicates mode in DIO flow.
Global Repair: we assume stable links and ranks (metrics), so no need
to periodically rebuild DODAG.  DODAG version only incremented under
catastrophic events (e.g.: administrative action).
Global Repair: we assume stable links and ranks (metrics), so no need
to periodically rebuild DODAG.  DODAG version only incremented under
catastrophic events (e.g., administrative action).
Every ACP node (RPL node) announces an IPv6 prefix covering the
address(es) used in the ACP node.  The prefix length depends on the
chosen addressing sub-scheme of the ACP address provisioned into the
certificate of the ACP node, e.g.: /127 for Zone Addressing Sub-
Scheme or /112 or /120 for Vlong addressing sub-scheme.  See
addressing for more details.
Every ACP node (RPL node) announces an IPv6 prefix covering the
address(es) used in the ACP node.  The prefix length depends on the
chosen addressing sub-scheme of the ACP address provisioned into the
certificate of the ACP node, e.g., /127 for Zone Addressing Sub-
Scheme or /112 or /120 for Vlong addressing sub-scheme.  See
addressing for more details.
Administrative Preference (RFC6552, 3.2.6 - to become root):
Indicated in DODAGPreference field of DIO message.
Administrative Preference (RFC6550, 3.2.6 - to become root):
Indicated in DODAGPreference field of DIO message.
Since channels are by default established between adjacent neighbors,
the resulting overlay network does hop by hop encryption.  Each node
decrypts incoming traffic from the ACP, and encrypts outgoing traffic
to its neighbors in the ACP.  Routing is discussed in routing.
Since channels are by default established between adjacent neighbors,
the resulting overlay network does hop-by-hop encryption.  Each node
decrypts incoming traffic from the ACP, and encrypts outgoing traffic
to its neighbors in the ACP.  Routing is discussed in routing.
There are no performance requirements against ACP implementations
defined in this document because the performance requirements depend
on the intended use case.  It is expected that full autonomic node
with a wide range of ASA can require high forwarding plane
performance in the ACP, for example for telemetry, but that
determination is for future work.  Implementations of ACP to solely
support traditional/SDN style use cases can benefit from ACP at lower
performance, especially if the ACP is used only for critical
operations, e.g.: when the data-plane is not available.  See I-
D.ietf-anima-stable-connectivity for more details.
In order to be independent of the data-plane configuration of global
IPv6 subnet addresses (that may not exist when the ACP is brought
up), Link-local secure channels MUST use IPv6 link local addresses
between adjacent neighbors.  The fully autonomic mechanisms in this
document only specify these link-local secure channels. remote-acp-
neighbors specifies extensions in which secure channels are tunnels.
For those, this requirement does not apply.
The Link-local secure channels specified in this document therefore
depend on basic IPv6 link-local functionality to be auto-enabled by
the ACP and prohibiting the data-plane from disabling it.  The ACP
also depends on being able to operate the secure channel protocol
(e.g.: IPsec / dTLS) across IPv6 link-local addresses, something that
may be an uncommon profile.  Functionally, these are the only
interactions with the data-plane that the ACP needs to have.
To mitigate these interactions with the data-plane, extensions to
this document may specify additional layer 2 or layer encapsulations
for ACP secure channels as well as other protocols to auto-discover
peer endpoints for such encapsulations (e.g.: tunneling across L3 or
use of L2 only encapsulations).
There are no performance requirements against ACP implementations
defined in this document because the performance requirements depend
on the intended use case.  It is expected that full autonomic node
with a wide range of ASA can require high forwarding plane
performance in the ACP, for example for telemetry.  Implementations
of ACP to solely support traditional/SDN style use cases can benefit
from ACP at lower performance, especially if the ACP is used only for
critical operations, e.g., when the Data-Plane is not available.  The
design of the ACP as specified in this document is intended to
support a wide range of performance options: It is intended to allow
software-only implementations at potentially low performance, but can
also support high performance options.  See RFC8368 for more details.
In order to be independent of the Data-Plane (routing and addressing)
the GRASP discovered (autonomic) ACP secure channels use IPv6 link
local addresses between adjacent neighbors.  Note: remote-acp-
neighbors specifies extensions in which secure channels are
configured tunnels operating over the Data-Plane, so those secure
channels cannot be independent of the Data-Plane.
To avoid that Data-Plane configuration can impact the operations of
the IPv6 (link-local) interface/address used for ACP channels,
appropriate implementation considerations are required.  If the IPv6
interface/link-local address is shared with the Data-Plane it needs
to be impossible to unconfigure/disable it through configuration.
Instead of sharing the IPv6 interface/link-local address, a separate
(virtual) interface with a separate IPv6 link-local address can be
used.  For example, the ACP interface could be run over a separate
MAC address of an underlying L2 (Ethernet) interface.  For more
details and options, see dp-dependency.
Note that other (non-ideal) implementation choices may introduce
additional undesired dependencies against the Data-Plane.  For
example shared code and configuration of the secure channel protocols
(IPsec / DTLS).
ACP secure Channel protocols do not need to perform MTU discovery
because they are built across L2 adjacencies - the MTU on both sides
connecting to the L2 connection are assumed to be consistent.
Extensions to ACP where the ACP is for example tunneled need to
consider how to guarantee MTU consistency.  This is a standard issue
with tunneling, not specific to running the ACP across it.  Transport
stacks running across ACP can perform normal PMTUD (Path MTU
Discovery).  Because the ACP is meant to be prioritize reliability
over performance, they MAY opt to only expect IPv6 minimum MTU (1280)
to avoid running into PMTUD implementation bugs or underlying link
MTU mismatch problems.
ACP secure Channel protocols do not need to perform MTU discovery
because they are built across L2 adjacencies - the MTU on both sides
connecting to the L2 connection are assumed to be consistent.
Extensions to ACP where the ACP is for example tunneled need to
consider how to guarantee MTU consistency.  This is an issue of
tunnels, not an issue of running the ACP across a tunnel.  Transport
stacks running across ACP can perform normal PMTUD (Path MTU
Discovery).  Because the ACP is meant to be prioritize reliability
over performance, they MAY opt to only expect IPv6 minimum MTU (1280)
to avoid running into PMTUD implementation bugs or underlying link
MTU mismatch problems.
Alice shows up with a previously unknown GRASP announcement (e.g.: on
a different link or with a different address announced in GRASP).
Even though loopback interfaces where originally designed to hold
only loopback addresses not reachable from outside the node, these
interfaces are also commonly used today to hold addresses reachable
from the outside.  They are meant to be reachable independent of any
external interface being operational, and therefore to be more
resilient.  These addresses on loopback interfaces can be thought of
as "node addresses" instead of "interface addresses", and that is
what ACP address(es) are.  This construct makes it therefore possible
to address ACP nodes with a well-defined set of addresses independent
of the number of external interfaces.
Alice shows up with a previously unknown GRASP announcement (e.g., on
a different link or with a different address announced in GRASP).
Even though Loopback interfaces were originally designed to hold only
Loopback addresses not reachable from outside the node, these
interfaces are also commonly used today to hold addresses reachable
from the outside.  They are meant to be reachable independent of any
external interface being operational, and therefore to be more
resilient.  These addresses on Loopback interfaces can be thought of
as "node addresses" instead of "interface addresses", and that is
what ACP address(es) are.  This construct makes it therefore possible
to address ACP nodes with a well-defined set of addresses independent
of the number of external interfaces.
ACP nodes MUST perform standard IPv6 operations across ACP virtual
interfaces including SLAAC (Stateless Address Auto-Configuration -
RFC4862) to assign their IPv6 link local address on the ACP virtual
interface and ND (Neighbor Discovery - RFC4861) to discover which
IPv6 link-local neighbor address belongs to which ACP secure channel
mapped to the ACP virtual interface.  This is independent of whether
the ACP virtual interface is point-to-point or multi-access.
ACP nodes MUST NOT derive their ACP virtual interface IPv6 link local
address from their IPv6 link-local address used on the underlying
interface (e.g.: the address that is used as the encapsulation
address in the ACP secure channel protocols defined in this
document).  This ensures that the ACP virtual interface operations
will not depend on the specifics of the encapsulation used by the ACP
secure channel and that attacks against SLAAC on the physical
interface will not introduce new attack vectors against the
operations of the ACP virtual interface.
ACP nodes MUST perform standard IPv6 operations across ACP virtual
interfaces including SLAAC (Stateless Address Auto-Configuration) -
RFC4862) to assign their IPv6 link local address on the ACP virtual
interface and ND (Neighbor Discovery - RFC4861) to discover which
IPv6 link-local neighbor address belongs to which ACP secure channel
mapped to the ACP virtual interface.  This is independent of whether
the ACP virtual interface is point-to-point or multi-access.
"Optimistic Duplicate Address Detection (DAD)" according to RFC4429
is RECOMMENDED because the likelihood for duplicates between ACP
nodes is highly improbable as long as the address can be formed from
a globally unique local assigned identifier (e.g., EUI-48/EUI-64, see
below).
The ACP virtual interface IPv6 link local address can be derived from
any appropriate local mechanism such as node local EUI-48 or EUI-64
("EUI" stands for "Extended Unique Identifier").  It MUST NOT depend
on something that is attackable from the Data-Plane such as the IPv6
link-local address of the underlying physical interface, which can be
attacked by SLAAC, or parameters of the secure channel encapsulation
header that may not be protected by the secure channel mechanism.
the GRASP Session ID).  If Bob and Charlies ACP would emulate a
multi-access virtual interface, then this would not happen, because
GRASPs flooding procedure does not replicate back packets to the
interface that they were received from.
the GRASP Session ID).  If Bob and Charlie's ACP would emulate a
multi-access virtual interface, then this would not happen, because
GRASPs flooding procedure does not replicate back packets to the
interface that they were received from.
RPL does support operations and correct routing table construction
across non-broadcast multi-access (NBMA) subnets.  This is common
when using many radio technologies.  When such NBMA subnets are used,
they MUST NOT be represented as ACP multi-access virtual interfaces
because the replication of IPv6 link-local multicast messages will
not reach all NBMA subnet neighbors.  In result, GRASP message
flooding would fail.  Instead, each ACP secure channel across such an
interface MUST be represented as a ACP point-to-point virtual
interface.  These requirements can be avoided by coupling the ACP
flooding mechanism for GRASP messages directly to RPL (flood GRASP
across DODAG), but such an enhancement is subject for future work.
RPL does support operations and correct routing table construction
across non-broadcast multi-access (NBMA) subnets.  This is common
when using many radio technologies.  When such NBMA subnets are used,
they MUST NOT be represented as ACP multi-access virtual interfaces
because the replication of IPv6 link-local multicast messages will
not reach all NBMA subnet neighbors.  In result, GRASP message
flooding would fail.  Instead, each ACP secure channel across such an
interface MUST be represented as a ACP point-to-point virtual
interface.  See also future-rpl.
A full mesh of ACP connections like this can creates fundamental
scale challenges.  The number of security associations of the secure
channel protocols will likely not scale arbitrarily, especially when
they leverage platform accelerated encryption/decryption.  Likewise,
any other ACP operations (such as routing) needs to scale to the
number of direct ACP neighbors.  An ACP router with just 4 physical
interfaces might be deployed into a LAN with hundreds of neighbors
connected via switches.  Introducing such a new unpredictable scaling
factor requirement makes it harder to support the ACP on arbitrary
platforms and in arbitrary deployments.
A full mesh of ACP connections can create fundamental scale
challenges.  The number of security associations of the secure
channel protocols will likely not scale arbitrarily, especially when
they leverage platform accelerated encryption/decryption.  Likewise,
any other ACP operations (such as routing) needs to scale to the
number of direct ACP neighbors.  An ACP router with just 4 physical
interfaces might be deployed into a LAN with hundreds of neighbors
connected via switches.  Introducing such a new unpredictable scaling
factor requirement makes it harder to support the ACP on arbitrary
platforms and in arbitrary deployments.
Predictable scaling requirements for ACP neighbors can most easily be
achieved if in topologies like these, ACP capable L2 switches can
ensure that discovery messages terminate on them so that neighboring
ACP routers and switches will only find the physically connected ACP
L2 switches as their candidate ACP neighbors.  With such a discovery
mechanism in place, the ACP and its security associations will only
need to scale to the number of physical interfaces instead of a
potentially much larger number of "LAN-connected" neighbors.  And the
ACP topology will follow directly the physical topology, something
which can then also be leveraged in management operations or by ASAs.
Predictable scaling requirements for ACP neighbors can most easily be
achieved if in topologies such as these, ACP capable L2 switches can
ensure that discovery messages terminate on them so that neighboring
ACP routers and switches will only find the physically connected ACP
L2 switches as their candidate ACP neighbors.  With such a discovery
mechanism in place, the ACP and its security associations will only
need to scale to the number of physical interfaces instead of a
potentially much larger number of "LAN-connected" neighbors.  And the
ACP topology will follow directly the physical topology, something
which can then also be leveraged in management operations or by ASAs.
This L2/L3 optimized approach is subject to "address stealing", e.g.:
where a device on one port uses addresses of a device on another
port.  This is a generic issue in L2 LANs and switches often already
have some form of "port security" to prohibit this.  They rely on NDP
or DHCP learning of which port/MAC-address and IPv6 address belong
together and block duplicates.  This type of function needs to be
enabled to prohibit DoS attacks.  Likewise the GRASP DULL instance
needs to ensure that the IPv6 address in the locator-option matches
the source IPv6 address of the DULL GRASP packet.
This L2/L3 optimized approach is subject to "address stealing", e.g.,
where a device on one port uses addresses of a device on another
port.  This is a generic issue in L2 LANs and switches often already
have some form of "port security" to prohibit this.  They rely on NDP
or DHCP learning of which port/MAC-address and IPv6 address belong
together and block duplicates.  This type of function needs to be
enabled to prohibit DoS attacks.  Likewise the GRASP DULL instance
needs to ensure that the IPv6 address in the locator-option matches
the source IPv6 address of the DULL GRASP packet.
In devices without such a mix of L2 port/interfaces and L3 interfaces
(to terminate any transport layer connections), implementation
details will differ.  Logically most simply every L2 port is
considered and used as a separate L3 subnet for all ACP operations.
The fact that the ACP only requires IPv6 link-local unicast and
multicast should make support for it on any type of L2 devices as
simple as possible, but the need to support secure channel protocols
may be a limiting factor to supporting ACP on such devices.  Future
options such as 802.1ae could improve that situation.
In devices without such a mix of L2 port/interfaces and L3 interfaces
(to terminate any transport layer connections), implementation
details will differ.  Logically most simply every L2 port is
considered and used as a separate L3 subnet for all ACP operations.
The fact that the ACP only requires IPv6 link-local unicast and
multicast should make support for it on any type of L2 devices as
simple as possible.
The Autonomic Control Plane can be used by management systems, such
as controllers or network management system (NMS) hosts (henceforth
called simply "NMS hosts"), to connect to devices (or other type of
nodes) through it.  For this, an NMS host must have access to the
ACP.  The ACP is a self-protecting overlay network, which allows by
default access only to trusted, autonomic systems.  Therefore, a
traditional, non-ACP NMS system does not have access to the ACP by
default, just like any other external node.
The Autonomic Control Plane can be used by management systems, such
as controllers or network management system (NMS) hosts (henceforth
called simply "NMS hosts"), to connect to devices (or other type of
nodes) through it.  For this, an NMS host must have access to the
ACP.  The ACP is a self-protecting overlay network, which allows by
default access only to trusted, autonomic systems.  Therefore, a
traditional, non-ACP NMS system does not have access to the ACP by
default, such as any other external node.
An ACP connect interface provides exclusively access to only the ACP.
This is likely insufficient for many NMS hosts.  Instead, they would
require a second "data-plane" interface outside the ACP for
connections between the NMS host and administrators, or Internet
based services, or for direct access to the data-plane.  The document
I-D.ietf-anima-stable-connectivity explains in more detail how the
ACP can be integrated in a mixed NOC environment.
An ACP connect interface provides exclusively access to only the ACP.
This is likely insufficient for many NMS hosts.  Instead, they would
require a second "Data-Plane" interface outside the ACP for
connections between the NMS host and administrators, or Internet
based services, or for direct access to the Data-Plane.  The document
RFC8368 explains in more detail how the ACP can be integrated in a
mixed NOC environment.
To limit the security impact of ACP connect, nodes supporting it
SHOULD implement a security mechanism to allow configuration/use of
ACP connect interfaces only on nodes explicitly targeted to be
deployed with it (such as those physically secure locations like a
NOC).  For example, the certificate of such node could include an
extension required to permit configuration of ACP connect interfaces.
This prohibits that a random ACP node with easy physical access that
is not meant to run ACP connect could start leaking the ACP when it
becomes compromised and the intruder configures ACP connect on it.
The full workflow including the mechanism by which a registrar would
select which node to give such a certificate to is subject to future
work.
To limit the security impact of ACP connect, nodes supporting it
SHOULD implement a security mechanism to allow configuration/use of
ACP connect interfaces only on nodes explicitly targeted to be
deployed with it (those in physically secure locations such as a
NOC).  For example, the registrar could disable the ability to enable
ACP connect on devices during enrollment and that property could only
be changed through re-enrollment.  See also role-assignments.
functions): An internal virtual subnet connecting out-of-band-
management interfaces of the VNFs to an ACP edge router VNF.
functions): An internal virtual subnet connecting out-of-band
management interfaces of the VNFs to an ACP edge router VNF.
This "internal" use of ACP connect approach should not considered to
be a "workaround" because in this case it is possible to build a
correct security model: It is not necessary to rely on unprovable
external physical security mechanisms as in the case of external NMS
hosts.  Instead, the orchestration of the ACP, the virtual subnets
and the software components can be done by trusted software that
could be considered to be part of the ANI (or even an extended ACP).
This software component is responsible to ensure that only trusted
software components will get access to that virtual subnet and that
only even more trusted software components will get access to both
the ACP virtual subnet and the data-plane (because those ACP users
could leak traffic between ACP and data-plane).  This trust could be
established for example through cryptographic means such signed
software packages.  The specification of these mechanisms is subject
to future work.
Note that ASA (Autonomic Software Agents) could also be software
components as described in this section, but further details of ASAs
are subject to future work.
ACP edge nodes, NMS hosts and software components that as described
in the previous section are meant to be composed via virtual
interfaces SHOULD support on the ACP connect subnet Stateless Address
Autoconfiguration (SLAAC - RFC4862) and route autoconfiguration
according to RFC4191.
This "internal" use of ACP connect approach should not considered to
be a "workaround" because in this case it is possible to build a
correct security model: It is not necessary to rely on unprovable
external physical security mechanisms as in the case of external NMS
hosts.  Instead, the orchestration of the ACP, the virtual subnets
and the software components can be done by trusted software that
could be considered to be part of the ANI (or even an extended ACP).
This software component is responsible for ensuring that only trusted
software components will get access to that virtual subnet and that
only even more trusted software components will get access to both
the ACP virtual subnet and the Data-Plane (because those ACP users
could leak traffic between ACP and Data-Plane).  This trust could be
established for example through cryptographic means such as signed
software packages.
ACP edge nodes, NMS hosts and software components that as described
in the previous section are meant to be composed via virtual
interfaces SHOULD support on the ACP connect subnet StateLess Address
Autoconfiguration (SLAAC - RFC4862) and route auto configuration
according to RFC4191.
To provide a single subnet into both ACP and data-plane, the ACP Edge
node needs to de-multiplex packets from NMS hosts into ACP VRF and
data-plane VRF.  This is sometimes called "VRF select".  If the ACP
VRF has no overlapping IPv6 addresses with the data-plane (as it
should), then this function can use the IPv6 Destination address.
The problem is Source Address Selection on the NMS Host(s) according
to RFC6724.
To provide a single subnet into both ACP and Data-Plane, the ACP Edge
node needs to de-multiplex packets from NMS hosts into ACP VRF and
Data-Plane.  This is sometimes called "VRF select".  If the ACP VRF
has no overlapping IPv6 addresses with the Data-Plane (as it should),
then this function can use the IPv6 Destination address.  The problem
is Source Address Selection on the NMS Host(s) according to RFC6724.
GRASP can and should be possible to use across ACP connect
interfaces, especially in the architectural correct solution when it
is used as a mechanism to connect Software (e.g.: ASA or legacy NMS
applications) to the ACP.  Given how the ACP is the security and
transport substrate for GRASP, the trustworthiness of nodes/software
allowed to participate in the ACP GRASP domain is one of the main
reasons why the ACP section describes no solution with non-ACP
routers participating in the ACP routing table.
ACP connect interfaces can be dealt with in the GRASP ACP domain like
any other ACP interface assuming that any physical ACP connect
interface is physically protected from attacks and that the connected
Software or NMS Hosts are equally trusted as that on other ACP nodes.
ACP edge nodes SHOULD have options to filter GRASP messages in and
out of ACP connect interfaces (permit/deny) and MAY have more fine-
grained filtering (e.g.: based on IPv6 address of originator or
objective).
GRASP can and should be possible to use across ACP connect
interfaces, especially in the architectural correct solution when it
is used as a mechanism to connect Software (e.g., ASA or legacy NMS
applications) to the ACP.  Given how the ACP is the security and
transport substrate for GRASP, the trustworthiness of nodes/software
allowed to participate in the ACP GRASP domain is one of the main
reasons why the ACP section describes no solution with non-ACP
routers participating in the ACP routing table.
ACP connect interfaces can be dealt with in the GRASP ACP domain the
same as any other ACP interface assuming that any physical ACP
connect interface is physically protected from attacks and that the
connected Software or NMS Hosts are equally trusted as that on other
ACP nodes.  ACP edge nodes SHOULD have options to filter GRASP
messages in and out of ACP connect interfaces (permit/deny) and MAY
have more fine-grained filtering (e.g., based on IPv6 address of
originator or objective).
On the ACP node, remote ACP neighbors are configured as follows.
Future work could transform this into a YANG (RFC7950) data model.
Explicit configuration of a remote-peer provides all the information
to build a secure channel without requiring a tunnel to that peer and
running DULL GRASP inside of it.
On the ACP node, remote ACP neighbors are configured explicitly.  The
parameters of such a "connection" are described in the following
ABNF.
Explicit configuration of a remote-peer according to this ABNF
provides all the information to build a secure channel without
requiring a tunnel to that peer and running DULL GRASP inside of it.
Configuration of port is only required for methods where no
defaults exist (e.g.: "dTLS").
Configuration of port is only required for methods where no
defaults exist (e.g., "DTLS").
Pmtu should be configurable to overcome issues/limitations of
PMTUD (Path MTU Discovery).
IKEv2/IPsec to remote peers should support the optional NAT-T
procedures (NAT Traversal).
An IPinIP, GRE or other form of pre-existing tunnel is configured
between two remote ACP peers and the virtual interfaces representing
the tunnel are configured to "ACP enable".  This will enable IPv6
link local addresses and DULL on this tunnel.  In result, the tunnel
is used for normal "L2 adjacent" candidate ACP neighbor discovery
with DULL and secure channel setup procedures described in this
document.
Pmtu should be configurable to overcome issues/limitations of Path
MTU Discovery (PMTUD).
IKEv2/IPsec to remote peers should support the optional NAT
Traversal (NAT-T) procedures.
An IPinIP, GRE or other form of pre-existing tunnel is configured
between two remote ACP peers and the virtual interfaces representing
the tunnel are configured for "ACP enable".  This will enable IPv6
link local addresses and DULL on this tunnel.  In result, the tunnel
is used for normal "L2 adjacent" candidate ACP neighbor discovery
with DULL and secure channel setup procedures described in this
document.
Future work could envisage an option where the edge nodes of the L3
cloud is configured to automatically forward ACP discovery messages
to the right exit point.  This optimisation is not considered in this
document.
There are few central dependencies: A certificate revocation list
(CRL) may not be available during a network partition; a suitable
policy to not immediately disconnect neighbors when no CRL is
available can address this issue.  Also, a registrar or Certificate
Authority might not be available during a partition.  This may delay
renewal of certificates that are to expire in the future, and it may
prevent the enrolment of new nodes during the partition.
There are few central dependencies: A certificate revocation list
(CRL) may not be available during a network partition; a suitable
policy to not immediately disconnect neighbors when no CRL is
available can address this issue.  Also, an ACP registrar or
Certificate Authority might not be available during a partition.
This may delay renewal of certificates that are to expire in the
future, and it may prevent the enrollment of new nodes during the
partition.
Highly resilient ACP designs can be built by using ACP registrars
with embedded sub-CA, as outlined in sub-ca.  As long as a partition
is left with one or more of such ACP registrars, it can continue to
enroll new candidate ACP nodes as long as the ACP registrars sub-CA
certificate does not expire.  Because the ACP addressing relies on
unique Registrar-IDs, a later re-merge of partitions will also not
cause problems with ACP addresses assigned during partitioning.
As explained in self-creation, the ACP is based on secure channels
built between nodes that have mutually authenticated each other with
their domain certificates.  The channels themselves are protected
using standard encryption technologies like DTLS or IPsec which
provide additional authentication during channel establishment, data
integrity and data confidentiality protection of data inside the ACP
and in addition, provide replay protection.
As explained in self-creation, the ACP is based on secure channels
built between nodes that have mutually authenticated each other with
their domain certificates.  The channels themselves are protected
using standard encryption technologies such as DTLS or IPsec which
provide additional authentication during channel establishment, data
integrity and data confidentiality protection of data inside the ACP
and in addition, provide replay protection.
The ACP also serves as protection (through authentication and
encryption) for protocols relevant to OAM that may not have secured
protocol stack options or where implementation or deployment of those
options fails on some vendor/product/customer limitations.  This
includes protocols such as SNMP, NTP/PTP, DNS, DHCP, syslog,
Radius/Diameter/TACACS, IPFIX/Netflow - just to name a few.
Protection via the ACP secure hop-by-hop channels for these protocols
is meant to be only a stopgap though: The ultimate goal is for these
and other protocols to use end-to-end encryption utilizing the domain
certificate and rely on the ACP secure channels primarily for zero-
touch reliable connectivity, but not primarily for security.
The ACP also serves as protection (through authentication and
encryption) for protocols relevant to OAM that may not have secured
protocol stack options or where implementation or deployment of those
options fail on some vendor/product/customer limitations.  This
includes protocols such as SNMP, NTP/PTP, DNS, DHCP, syslog,
Radius/Diameter/TACACS, IPFIX/Netflow - just to name a few.
Protection via the ACP secure hop-by-hop channels for these protocols
is meant to be only a stopgap though: The ultimate goal is for these
and other protocols to use end-to-end encryption utilizing the domain
certificate and rely on the ACP secure channels primarily for zero-
touch reliable connectivity, but not primarily for security.
The remaining attack vector would be to attack the underlying AN
protocols themselves, either via directed attacks or by denial-of-
service attacks.  However, as the ACP is built using link-local IPv6
address, remote attacks are impossible.  The ULA addresses are only
reachable inside the ACP context, therefore, unreachable from the
data-plane.  Also, the ACP protocols should be implemented to be
attack resistant and not consume unnecessary resources even while
under attack.
The remaining attack vector would be to attack the underlying ACP
protocols themselves, either via directed attacks or by denial-of-
service attacks.  However, as the ACP is built using link-local IPv6
address, remote attacks are impossible.  The ULA addresses are only
reachable inside the ACP context, therefore, unreachable from the
Data-Plane.  Also, the ACP protocols should be implemented to be
attack resistant and not consume unnecessary resources even while
under attack.
Group members must overall the secured so that there are no easy way
to compromise them, such as data-plane accessible privilege level
with simple passwords.  This is a lot easier to do in devices whose
software is designed from the ground up with security in mind than
with legacy software based system where ACP is added on as another
feature.
Group members must be protected against attackers so that there is no
easy way to compromise them, or use them as a proxy for attacking
other devices across the ACP.  For example, management plane
functions (transport ports) should only be reachable from the ACP but
not the Data-Plane.  Especially for those management plane functions
that have no good protection by themselves because they do not have
secure end-to-end transport and to whom ACP does not only provides
automatic reliable connectivity but also protection against attacks.
Protection across all potential attack vectors is typically easier to
do in devices whose software is designed from the ground up with
security in mind than with legacy software based systems where the
ACP is added on as another feature.
Further security can be achieved by constraining communication
patterns inside the ACP, for example through roles that could be
encoded into the domain certificates.  This is subject for future
work.
The following sections cover topics that are beyond the primary cope
of this document (e.g.: bootstrap), that explain decisions made in
this document (e.g.: choice of GRASP) or that explain desirable
extensions or implementation details for the ACP that are not
considered to be appropriate to standardize in this document.
I-D.ietf-anima-bootstrapping-keyinfra (BRSKI) describes how nodes
with an IDevID certificate can securely and zero-touch enroll with a
domain certificate (LDevID) to support the ACP.  BRSKI also leverages
the ACP to enable zero touch bootstrap of new nodes across networks
without any configuration requirements across the transit nodes
(e.g.: no DHCP/DS forwarding/server setup).  This includes otherwise
not configured networks as described in secure-bootstrap.  Therefore
BRSKI in conjunction with ACP provides for a secure and zero-touch
management solution for complete networks.  Nodes supporting such an
infrastructure (BRSKI and ACP) are called ANI nodes (Autonomic
Networking Infrastructure), see I-D.ietf-anima-reference-model.
Nodes that do not support an IDevID but only an (insecure) vendor
specific Unique Device Identifier (UDI) or nodes whose manufacturer
does not support a MASA could use some future security reduced
version of BRSKI.
When BRSKI is used to provision a domain certificate (which is called
enrollment), the registrar (acting as an EST server) must include the
subjectAltName / rfc822Name encoded ACP address and domain name to
the enrolling node (called pledge) via its response to the pledges
EST CSR Attribute request that is mandatory in BRSKI.
The Certificate Authority in an ACP network must not change the
subjectAltName / rfc822Name in the certificate.  The ACP nodes can
therefore find their ACP address and domain using this field in the
domain certificate, both for themselves, as well as for other nodes.
The use of BRSKI in conjunction with the ACP can also help to further
simplify maintenance and renewal of domain certificates.  Instead of
relying on CRL, the lifetime of certificates can be made extremely
small, for example in the order of hours.  When a node fails to
connect to the ACP within its certificate lifetime, it cannot connect
to the ACP to renew its certificate across it (using just EST), but
it can still renew its certificate as an "enrolled/expired pledge"
via the BRSKI bootstrap proxy.  This requires only that the BRSKI
registrar honors expired domain certificates and that the pledge
first attempts to perform TLS authentication for BRSKI bootstrap with
its expired domain certificate - and only reverts to its IDevID when
this fails.  This mechanism could also render CRLs unnecessary
because the BRSKI registrar in conjunction with the CA would not
renew revoked certificates - only a "no-not-renew" list would be
necessary on registrars/CA.
In the absence of BRSKI or less secure variants thereof, provisioning
of certificates may involve one or more touches or non-standardized
automation.  Node vendors usually support provisioning of
certificates into nodes via PKCS#7 (see RFC2315) and may support this
provisioning through vendor specific models via Netconf (RFC6241).
If such nodes also support Netconf Zero-Touch (I-D.ietf-netconf-
zerotouch) then this can be combined to zero-touch provisioning of
domain certificates into nodes.  Unless there are equivalent
integration of Netconf connections across the ACP as there is in
BRSKI, this combination would not support zero-touch bootstrap across
a not configured network though.
The following sections document important operational aspects of the
ACP.  They are not normative because they do not impact the
interoperability between components of the ACP, but they include
recommendations/requirements for the internal operational model
beneficial or necessary to achieve the desired use-case benefits of
the ACP (see usage).
diagnostics describes recommended operator diagnostics
capabilities of ACP nodes.  The have been derived from diagnostic
of a commercially available ACP implementation.
registrar-considerations describes high level how an ACP registrar
needs to work, what its configuration parameters are and specific
issues impacting the choices of deployment design due to renewal
and revocation issues.  It describes a model where ACP Registrars
have their own sub-CA to provide the most distributed deployment
option for ACP Registrars, and it describes considerations for
centralized policy control of ACP Registrar operations.
enabling-acp describes suggested ACP node behavior and operational
interfaces (configuration options) to manage the ACP in so-called
greenfield devices (previously unconfigured) and brownfield
devices (preconfigured).
The recommendations and suggestions of this chapter were derived from
operational experience gained with a commercially available pre-
standard ACP implementation.
Developing the logic to identify common issues requires
operational experience with the components of the ANI.  Letting
each management system define its own analysis is inefficient.  As
much as possible, future work should attempt to standardize data
models that support common error diagnostic.
Developing the logic to identify common issues requires
operational experience with the components of the ANI.  Letting
each management system define its own analysis is inefficient.
Does the certificate authenticate against the trust anchor ?
Has it been revoked ?
Was the last scheduled attempt to retrieve a CRL successful
(e.g.: do we know that our CRL information is up to date).
Is the certificate valid: validity start time in the past,
expiration time in the future ?
Does the certificate have a correctly formatted ACP information
field ?
Was the ACP VRF successfully created ?
Is ACP enabled on one or more interfaces that are up and running ?
If all this looks good, the ACP should be running locally "fine" -
but we did not check any ACP neighborships.
Question: why does the node not create a working ACP connection to a
neighbor on an interface ?
Is the interface physically up ? Does it have an IPv6 link-local
address ?
Is it enabled for ACP ?
Do we successfully send DULL GRASP messages to the interface (link
layer errors) ?
Do we receive DULL GRASP messages on the interface ? If not, some
intervening L2 equipment performing bad MLD snooping could have
caused problems.  Provide e.g.: diagnostics of the MLD querier
IPv6 and MAC address.
Do we see the ACP objective in any DULL GRASP message from that
interface ? Diagnose the supported secure channel methods.
Do we know the MAC address of the neighbor with the ACP objective
? If not, diagnose SLAAC/ND state.
When did we last attempt to build an ACP secure channel to the
neighbor ?
Did the neighbor close the connection on us or did we close the
connection on it because the domain certificate membership
failed ?
Does the certificate authenticate against the trust anchor?
Has it been revoked?
Was the last scheduled attempt to retrieve a CRL successful
(e.g., do we know that our CRL information is up to date).
Is the certificate valid: validity start time in the past,
expiration time in the future?
Does the certificate have a correctly formatted ACP information
field?
Was the ACP VRF successfully created?
Is ACP enabled on one or more interfaces that are up and running?
If all this looks good, the ACP should be running locally "fine" -
but we did not check any ACP neighbor relationships.
Question: why does the node not create a working ACP connection to a
neighbor on an interface?
Is the interface physically up?  Does it have an IPv6 link-local
address?
Is it enabled for ACP?
Do we successfully send DULL GRASP messages to the interface (link
layer errors)?
Do we receive DULL GRASP messages on the interface?  If not, some
intervening L2 equipment performing bad MLD snooping could have
caused problems.  Provide e.g., diagnostics of the MLD querier
IPv6 and MAC address.
Do we see the ACP objective in any DULL GRASP message from that
interface?  Diagnose the supported secure channel methods.
Do we know the MAC address of the neighbor with the ACP objective?
If not, diagnose SLAAC/ND state.
When did we last attempt to build an ACP secure channel to the
neighbor?
Did the neighbor close the connection on us or did we close the
connection on it because the domain certificate membership
failed?
The neighbors certificate does not have the same domain
(or no domain at all).  Diagnose domain-name and
potentially other other cert info.
The neighbors certificate does not have the same domain
(or no domain at all).  Diagnose domain-name and
potentially other cert info.
Any other connection issues in e.g.: IKEv2 / IPsec, dTLS ?".
Are there one or more active ACP neighbors with secure channels ?
Is the RPL routing protocol for the ACP running ?
Is there a default route to the root in the ACP routing table ?
Is there for each direct ACP neighbor not reachable over the ACP
virtual interface to the root a route in the ACP routing table ?
Is ACP GRASP running ?
Is at least one SRV.est objective cached (to support certificate
renewal) ?
Is BRSKI proxy operating normally on all interfaces where ACP is
operating ?
Any other connection issues in e.g., IKEv2 / IPsec, DTLS?.
Question: Is the ACP operating correctly across its secure channels?
Are there one or more active ACP neighbors with secure channels?
Is the RPL routing protocol for the ACP running?
Is there a default route to the root in the ACP routing table?
Is there for each direct ACP neighbor not reachable over the ACP
virtual interface to the root a route in the ACP routing table?
Is ACP GRASP running?
Is at least one SRV.est objective cached (to support certificate
renewal)?
Is BRSKI proxy operating normally on all interfaces where ACP is
operating?
BRSKI does not allow for a neighboring device to identify the
pledges certificate (IDevID).  Only the selected BRSKI-registrar
can do this, but it may be difficult to disseminate information
about undesired pledges from those registrars to locations/nodes
where information about those pledges is desired.
LLDP disseminates information about nodes to their immediate
neighbors, such as node model/type/software and interface name/
number of the connection.  This information is often helpful or
even necessary in network diagnostics.  It can equally considered
to be too insecure to make this information available unprotected
to all possible neighbors.
BRSKI does not allow for a neighboring device to identify the
pledges certificate (IDevID).  Only the selected BRSKI registrar
can do this, but it may be difficult to disseminate information
about undesired pledges from those BRSKI registrars to locations/
nodes where information about those pledges is desired.
The Link Layer Discovery Protocol (LLDP, LLDP) disseminates
information about nodes to their immediate neighbors, such as node
model/type/software and interface name/number of the connection.
This information is often helpful or even necessary in network
diagnostics.  It can equally considered to be too insecure to make
this information available unprotected to all possible neighbors.
Determine if LLDP should be a recommended functionality for ANI
devices to improve diagnostics, and if so, which information
elements it should signal (insecure).
In alternative to LLDP, A DULL GRASP diagnostics objective could
be defined to carry these information elements.
The IDevID of BRSKI pledges should be included in the selected
insecure diagnostics option.
A richer set of diagnostics information should be made available
via the secured ACP channels, using either single-hop GRASP or
network wide "topology discovery" mechanisms.
Both ACP and BRSKI require interfaces to be operational enough to
support sending/receiving their packets.  In node types where
interfaces are by default (e.g.: without operator configuration)
enabled, such as most L2 switches, this would be less of a change in
behavior than in most L3 devices (e.g.: routers), where interfaces
are by default disabled.  In almost all network devices it is common
though for configuration to change interfaces to a physically
disabled state and that would break the ACP.
As described in acp-registrars, the ACP addressing mechanism is
designed to enable lightweight, distributed and uncoordinated ACP
registrars that are providing ACP address prefixes to candidate ACP
nodes by enrolling them with an ACP domain certificate into an ACP
domain via any appropriate mechanism/protocol, automated or not.
This section discusses informatively more details and options for ACP
registrars.
This section summarizes and discusses the interactions with other
entities required by an ACP registrar.
To orchestrate enrolling a candidate ACP node autonomically, the ACP
registrar can rely on the ACP and use Proxies to reach the candidate
ACP node, therefore allowing minimum pre-existing (auto-)configured
network services on the candidate ACP node.  BRSKI defines the BRSKI
proxy, a design that can be adopted for various protocols that
Pledges/candidate ACP nodes could want to use, for example BRSKI over
CoAP (Constrained Application Protocol), or proxying of Netconf.
To reach a trust anchor unaware of the ACP, the ACP registrar would
use the Data-Plane.  ACP and Data-Plane in an ACP registrar could
(and by default should be) completely isolated from each other at the
network level.  Only applications such as the ACP registrar would
need the ability for their transport stacks to access both.
In non-autonomic enrollment options, the Data-Plane between a ACP
registrar and the candidate ACP node needs to be configured first.
This includes the ACP registrar and the candidate ACP node.  Then any
appropriate set of protocols can be used between ACP registrar and
candidate ACP node to discover the other side, and then connect and
enroll (configure) the candidate ACP node with an ACP domain
certificate.  Netconf ZeroTouch (I-D.ietf-netconf-zerotouch) is an
example protocol that could be used for this.  BRSKI using optional
discovery mechanisms is equally a possibility for candidate ACP nodes
attempting to be enrolled across non-ACP networks, such as the
Internet.
When candidate ACP nodes have secure bootstrap, such as BRSKI
Pledges, they will not trust to be configured/enrolled across the
network, unless being presented with a voucher (see RFC8366)
authorizing the network to take possession of the node.  An ACP
registrar will then need a method to retrieve such a voucher, either
offline, or online from a MASA (Manufacturer Authorized Signing
Authority).  BRSKI and Netconf ZeroTouch are two protocols that
include capabilities to present the voucher to the candidate ACP
node.
An ACP registrar could operate EST for ACP certificate renewal and/or
act as a CRL Distribution point.  A node performing these services
does not need to support performing (initial) enrollment, but it does
require the same above described connectivity as an ACP registrar:
via the ACP to ACP nodes and via the Data-Plane to the trust anchor
and other sources of CRL information.
A URL to the trust anchor (root CA) and credentials so that the
ACP registrar can let the trust anchor sign candidate ACP member
certificates.
The ACP domain-name.
The Registrar-ID to use.  This could default to a MAC address of
the ACP registrar.
For recovery, the next-useable Node-IDs for zone (Zone-ID=0) sub-
addressing scheme, for Vlong /112 and for Vlong /1120 sub-
addressing scheme.  These IDs would only need to be provisioned
after recovering from a crash.  Some other mechanism would be
required to remember these IDs in a backup location or to recover
them from the set of currently known ACP nodes.
Policies if candidate ACP nodes should receive a domain
certificate or not, for example based on the devices LDevID as in
BRSKI.  The ACP registrar may have a whitelist or blacklist of
devices serialNumbers from their LDevID.
Policies what type of address prefix to assign to a candidate ACP
devices, based on likely the same information.
For BRSKI or other mechanisms using vouchers: Parameters to
determine how to retrieve vouchers for specific type of secure
bootstrap candidate ACP nodes (such as MASA URLs), unless this
information is automatically learned such as from the LDevID of
candidate ACP nodes (as defined in BRSKI).
When an ACP node renews/rekeys its certificate, it may end up doing
so via a different registrar (e.g., EST server) than the one it
originally received its ACP domain certificate from, for example
because that original ACP registrar is gone.  The ACP registrar
through which the renewal/rekeying is performed would by default
trust the ACP domain information from the ACP nodes current ACP
domain certificate and maintain this information so that the ACP node
maintains its ACP address prefix.  In EST renewal/rekeying, the ACP
nodes current ACP domain certificate is signaled during the TLS
handshake.
The ACP registrars cannot directly assign certificates to nodes
and therefore needs an "online" connection to the trust anchor
(root CA).
Recovery from a compromised ACP registrar is difficult.  When an
ACP registrar is compromised, it can insert for example
conflicting ACP domain information and create thereby an attack
against other ACP nodes through the ACP routing protocol.
Even when such a malicious ACP registrar is detected, resolving the
problem may be difficult because it would require identifying all the
wrong ACP domain certificates assigned via the ACP registrar after it
was compromised.  And without additional centralized tracking of
assigned certificates there is no way to do this.
In situations, where either of the above two limitations are an
issue, ACP registrars could also be sub-CAs.  This removes the need
for connectivity to a root-CA whenever an ACP node is enrolled, and
reduces the need for connectivity of such an ACP registrar to a root-
CA to only those times when it needs to renew its own certificate.
The ACP registrar would also now use its own (sub-CA) certificate to
enroll and sign the ACP nodes certificates, and therefore it is only
necessary to revoke a compromised ACP registrars sub-CA certificate.
Or let it expire and not renew it, when the certificate of the sub-CA
is appropriately short-lived.
As the ACP domain membership check verifies a peer ACP node's ACP
domain certificate trust chain, it will also verify the signing
certificate which is the compromised/revoked sub-CA certificate.
Therefore ACP domain membership for an ACP node enrolled from a
compromised ACP registrar will fail.
ACP nodes enrolled by a compromised ACP registrar would automatically
fail to establish ACP channels and ACP domain certificate renewal via
EST and therefore revert to their role as a candidate ACP members and
attempt to get a new ACP domain certificate from an ACP registrar -
for example, via BRSKI.  In result, ACP registrars that have an
associated sub-CA makes isolating and resolving issues with
compromised registrars easier.
Note that ACP registrars with sub-CA functionality also can control
the lifetime of ACP domain certificates easier and therefore also be
used as a tool to introduce short lived certificates and not rely on
CRL, whereas the certificates for the sub-CAs themselves could be
longer lived and subject to CRL.
Which candidate ACP node is permitted or not permitted into an ACP
domain.  This may not be a decision to be taken upfront, so that a
per-serialNumber policy can be loaded into ever ACP registrar.
Instead, it may better be decided in real-time including
potentially a human decision in a NOC.
Tracking of all enrolled ACP nodes and their certificate
information.  For example in support of revoking individual ACP
nodes certificates.
More flexible policies what type of address prefix or even what
specific address prefix to assign to a candidate ACP node.
These and other operations could be introduced more easily by
introducing a centralized Policy Management System (PMS) and
modifying ACP registrar behavior so that it queries the PMS for any
policy decision occurring during the candidate ACP node enrollment
process and/or the ACP node certificate renewal process.  For
example, which ACP address prefix to assign.  Likewise the ACP
registrar would report any relevant state change information to the
PMS as well, for example when a certificate was successfully enrolled
onto a candidate ACP node.
Both ACP and BRSKI require interfaces to be operational enough to
support sending/receiving their packets.  In node types where
interfaces are by default (e.g., without operator configuration)
enabled, such as most L2 switches, this would be less of a change in
behavior than in most L3 devices (e.g.: routers), where interfaces
are by default disabled.  In almost all network devices it is common
though for configuration to change interfaces to a physically
disabled state and that would break the ACP.
Both BRSKI and ACP require link-local only IPv6 operations on
interfaces and DULL GRASP.  IPv6 link-local operations means the
minimum signaling to auto-assign an IPv6 link-local address and talk
to neighbors via their link-local address: SLAAC (Stateless Address
Auto-Configuration - RFC4862) and ND (Neighbor Discovery - RFC4861).
When the device is a BRSKI pledge, it may also require TCP/TLS
connections to BRSKI proxies on the interface.  When the device has
keying material, and the ACP is running, it requires DULL GRASP
packets and packets necessary for the secure-channel mechanism it
supports, e.g.: IKEv2 and IPsec ESP packets or dTLS packets to the
IPv6 link-local address of an ACP neighbor on the interface.  It also
requires TCP/TLS packets for its BRSKI proxy functionality, if it
does support BRSKI.
Both BRSKI and ACP require link-local only IPv6 operations on
interfaces and DULL GRASP.  IPv6 link-local operations means the
minimum signaling to auto-assign an IPv6 link-local address and talk
to neighbors via their link-local address: SLAAC (Stateless Address
Auto-Configuration - RFC4862) and ND (Neighbor Discovery - RFC4861).
When the device is a BRSKI pledge, it may also require TCP/TLS
connections to BRSKI proxies on the interface.  When the device has
keying material, and the ACP is running, it requires DULL GRASP
packets and packets necessary for the secure-channel mechanism it
supports, e.g., IKEv2 and IPsec ESP packets or DTLS packets to the
IPv6 link-local address of an ACP neighbor on the interface.  It also
requires TCP/TLS packets for its BRSKI proxy functionality, if it
does support BRSKI.
important in other cases (see below).
important in other cases (see below, down-fast-state-propagation).
"Physical down" state propagates on many interface types (e.g.:
Ethernet) to the other side.  This can trigger fast L2/L3 protocol
reaction on the other side and "admin down" would not have the same
(fast) result.
"Physical down" state propagates on many interface types (e.g.,
Ethernet) to the other side.  This can trigger fast L2/L3 protocol
reaction on the other side and "admin down" would not have the same
(fast) result.
Ideally, fast physical state propagation is replaced by fast software
driven state propagation.  For example a DULL GRASP "admin-state"
objective could be used to autoconfigure a BFD session between the
two sides of the link that would be used to propagate the "up" vs.
admin down state.
Ideally, fast physical state propagation is replaced by fast software
driven state propagation.  For example a DULL GRASP "admin-state"
objective could be used to auto configure a Bidirectional Forwarding
Protocol (BFD, RFC5880) session between the two sides of the link
that would be used to propagate the "up" vs. admin down state.
"Physical down" is performed to diagnose low-level interface behavior
when higher layer services (e.g.: IPv6) are not working.  Especially
Ethernet links are subject to a wide variety of possible wrong
configuration/cablings if they do not support automatic selection of
variable parameters such as speed (10/100/1000 Mbps), crossover
(Auto-MDIX) and connector (fiber, copper - when interfaces have
multiple but can only enable one at a time).  The need for low level
link diagnostic can therefore be minimized by using fully
autoconfiguring links.
"Physical down" is performed to diagnose low-level interface behavior
when higher layer services (e.g., IPv6) are not working.  Especially
Ethernet links are subject to a wide variety of possible wrong
configuration/cablings if they do not support automatic selection of
variable parameters such as speed (10/100/1000 Mbps), crossover
(Auto-MDIX) and connector (fiber, copper - when interfaces have
multiple but can only enable one at a time).  The need for low level
link diagnostic can therefore be minimized by using fully auto
configuring links.
Power consumption of "physical down" interfaces may be significantly
lower than those in "admin down" state, for example on long range
fiber interfaces.  Assuming reasonable clocks on devices, mechanisms
for infrequent periodic probing could allow to automatically
establish ACP connectivity across such links.  Bring up interfaces
for 5 seconds to probe if there is an ACP neighbor on the remote end
every 500 seconds = 1% power consumption.
Power consumption of "physical down" interfaces, may be significantly
lower than those in "admin down" state, for example on long-range
fiber interfaces.  Bringing up interfaces, for example to probe
reachability, may also consume additional power.  This can make these
type of interfaces inappropriate to operate purely for the ACP when
they are not currently needed for the Data-Plane.
If the tunnel would connect two previously disjoint ACP regions, then
it likely would be useful for the ACP.  A data-plane tunnel could
also run across nodes without ACP and provide additional connectivity
for an already connected ACP network.  The benefit of this additional
ACP redundancy has to be weighed against the problems of relying on
the data-plane.  If a tunnel connects two separate ACP regions: how
many tunnels should be created to connect these ACP regions reliably
enough ? Between which nodes ? These are all standard tunneled
network design questions not specific to the ACP, and there are no
generic fully automated answers.
If the tunnel would connect two previously disjoint ACP regions, then
it likely would be useful for the ACP.  A Data-Plane tunnel could
also run across nodes without ACP and provide additional connectivity
for an already connected ACP network.  The benefit of this additional
ACP redundancy has to be weighed against the problems of relying on
the Data-Plane.  If a tunnel connects two separate ACP regions: how
many tunnels should be created to connect these ACP regions reliably
enough?  Between which nodes?  These are all standard tunneled
network design questions not specific to the ACP, and there are no
generic fully automated answers.
The goal of automatically setting "ACP/ANI enable" on interfaces
(native or not) is to eliminate unnecessary "touches" to the node to
make its operation as much as possible "zero-touch" with respect to
ACP/ANI.  If there are "unavoidable touches" such a creating/
configuring a non-native interface or provisioning credentials for a
native interface, then "ACP/ANI enable" should be added as an option
to that "touch".  If a wrong "touch" is easily fixed (not creating
another high-cost touch), then the default should be not to enable
ANI/ACP, and if it is potentially expensive or slow to fix (e.g.:
parameters on SIM card shipped to remote location), then the default
should be to enable ACP/ANI.
The goal of automatically setting "ACP/ANI enable" on interfaces
(native or not) is to eliminate unnecessary "touches" to the node to
make its operation as much as possible "zero-touch" with respect to
ACP/ANI.  If there are "unavoidable touches" such a creating/
configuring a non-native interface or provisioning credentials for a
native interface, then "ACP/ANI enable" should be added as an option
to that "touch".  If a wrong "touch" is easily fixed (not creating
another high-cost touch), then the default should be not to enable
ANI/ACP, and if it is potentially expensive or slow to fix (e.g.,
parameters on SIM card shipped to remote location), then the default
should be to enable ACP/ANI.
Executing global "ACP/ANI enable [up-if-only]" on each node is the
only command necessary to create an ACP across a network of
brownfield nodes once all the nodes have a domain certificate.  When
BRSKI is used ("ANI enable"), provisioning of the certificates only
requires set-up of a single BRSKI-registrar node which could also
implement a CA for the network.  This is the most simple way to
introduce ACP/ANI into existing (== brownfield) networks.
Executing global "ACP/ANI enable [up-if-only]" on each node is the
only command necessary to create an ACP across a network of
brownfield nodes once all the nodes have a domain certificate.  When
BRSKI is used ("ANI enable"), provisioning of the certificates only
requires set-up of a single BRSKI registrar node which could also
implement a CA for the network.  This is the most simple way to
introduce ACP/ANI into existing (== brownfield) networks.
Nodes supporting full ANI functionality set "ANI enable"
automatically when they decide that they are greenfield, e.g.: that
they are powering on from factory condition.  They will then put all
native interfaces into "admin down" state and start to perform BRSKI
pledge functionality - and once a domain certificate is enrolled they
automatically enable ACP.
Nodes supporting full ANI functionality set "ANI enable"
automatically when they decide that they are greenfield, e.g., that
they are powering on from factory condition.  They will then put all
native interfaces into "admin down" state and start to perform BRSKI
pledge functionality - and once a domain certificate is enrolled they
automatically enable ACP.
Attempts for BRSKI pledge operations in greenfield state should
terminate automatically when another method of configuring the node
is used.  Methods that indicate some form of physical possession of
the device such as configuration via the serial console could lead to
immediate termination of BRSKI, while other parallel
autoconfiguration methods subject to remote attacks might lead to
BRSKI termination only after they were successful.  Details of this
may vary widely over different type of nodes.  When BRSKI pledge
operation terminates, this will automatically unset "ANI enable" and
should terminate any temporarily needed state on the device to
perform BRSKI - DULL GRASP, BRSKI pledge and any IPv6 configuration
on interfaces.
Attempts for BRSKI pledge operations in greenfield state should
terminate automatically when another method of configuring the node
is used.  Methods that indicate some form of physical possession of
the device such as configuration via the serial console port could
lead to immediate termination of BRSKI, while other parallel auto
configuration methods subject to remote attacks might lead to BRSKI
termination only after they were successful.  Details of this may
vary widely over different type of nodes.  When BRSKI pledge
operation terminates, this will automatically unset "ANI enable" and
should terminate any temporarily needed state on the device to
perform BRSKI - DULL GRASP, BRSKI pledge and any IPv6 configuration
on interfaces.
Disabling ANI/ACP by undoing "ACP/ANI enable" is a risk for the
reliable operations of the ACP if it can be executed by mistake or
unauthorized.  This behavior could be influenced through some
additional property in the certificate (e.g.: in the domain
information extension field) subject to future work: In an ANI
deployment intended for convenience, disabling it could be allowed
without further constraints.  In an ANI deployment considered to be
critical more checks would be required.  One very controlled option
would be to not permit these commands unless the domain certificate
has been revoked or is denied renewal.  Configuring this option would
be a parameter on the BRSKI registrar(s).  As long as the node did
not receive a domain certificate, undoing "ANI/ACP enable" should not
have any additional constraints.
Disabling ANI/ACP by undoing "ACP/ANI enable" is a risk for the
reliable operations of the ACP if it can be executed by mistake or
unauthorized.  This behavior could be influenced through some
additional property in the certificate (e.g., in the domain
information extension field) subject to future work: In an ANI
deployment intended for convenience, disabling it could be allowed
without further constraints.  In an ANI deployment considered to be
critical more checks would be required.  One very controlled option
would be to not permit these commands unless the domain certificate
has been revoked or is denied renewal.  Configuring this option would
be a parameter on the BRSKI registrar(s).  As long as the node did
not receive a domain certificate, undoing "ANI/ACP enable" should not
have any additional constraints.
This section discusses why GRASP DULL was chosen as the discovery
protocol for L2 adjacent candidate ACP neighbors.  The contenders
considered where GRASP, mDNS or LLDP.
LLDP (and Cisco's similar CDP) are example of L2 discovery protocols
that terminate their messages on L2 ports.  If those protocols would
be chosen for ACP neighbor discovery, ACP neighbor discovery would
therefore also terminate on L2 ports.  This would prevent ACP
construction over non-ACP capable but LLDP or CDP enabled L2
switches.  LLDP has extensions using different MAC addresses and this
could have been an option for ACP discovery as well, but the
additional required IEEE standardization and definition of a profile
for such a modified instance of LLDP seemed to be more work than the
benefit of "reusing the existing protocol" LLDP for this very simple
purpose.
mDNS RFC6762 with DNS-SD RRs (Resource Records) as defined in RFC6763
is a key contender as an ACP discovery protocol. because it relies on
link-local IP multicast, it does operates at the subnet level, and is
also found in L2 switches.  The authors of this document are not
aware of mDNS implementation that terminate their mDNS messages on L2
ports instead of the subnet level.  If mDNS was used as the ACP
discovery mechanism on an ACP capable (L3)/L2 switch as outlined in
acp-l2-switches, then this would be necessary to implement.  It is
likely that termination of mDNS messages could only be applied to all
mDNS messages from such a port, which would then make it necessary to
software forward any non-ACP related mDNS messages to maintain prior
non-ACP mDNS functionality.  Adding support for ACP into such L2
switches with mDNS could therefore create regression problems for
prior mDNS functionality on those nodes.  With low performance of
software forwarding in many L2 switches, this could also make the ACP
risky to support on such L2 switches.
If mDNS was not already existing in a node, it would be more work to
implement than DULL GRASP, and if an existing implementation of mDNS
was used, it would likely be more code space than a separate
implementation of DULL GRASP or a shared implementation of DULL GRASP
and GRASP in the ACP.
This Appendix explains why RPL - "IPv6 Routing Protocol for Low-Power
and Lossy Networks (RFC6550 was chosen as the default (and in this
specification only) routing protocol for the ACP.  The choice and
above explained profile was derived from a pre-standard
implementation of ACP that was successfully deployed in operational
networks.
Self-management: The ACP must build automatically, without human
intervention.  Therefore routing protocol must also work
completely automatically.  RPL is a simple, self-managing
protocol, which does not require zones or areas; it is also self-
configuring, since configuration is carried as part of the
protocol (see Section 6.7.6 of RFC6550).
Scale: The ACP builds over an entire domain, which could be a
large enterprise or service provider network.  The routing
protocol must therefore support domains of 100,000 nodes or more,
ideally without the need for zoning or separation into areas.  RPL
has this scale property.  This is based on extensive use of
default routing.  RPL also has other scalability improvements,
such as selecting only a subset of peers instead of all possible
ones, and trickle support for information synchronization.
Low resource consumption: The ACP supports traditional network
infrastructure, thus runs in addition to traditional protocols.
The ACP, and specifically the routing protocol must have low
resource consumption both in terms of memory and CPU requirements.
Specifically, at edge nodes, where memory and CPU are scarce,
consumption should be minimal.  RPL builds a destination-oriented
directed acyclic graph (DODAG), where the main resource
consumption is at the root of the DODAG.  The closer to the edge
of the network, the less state needs to be maintained.  This
adapts nicely to the typical network design.  Also, all changes
below a common parent node are kept below that parent node.
Support for unstructured address space: In the Autonomic
Networking Infrastructure, node addresses are identifiers, and may
not be assigned in a topological way.  Also, nodes may move
topologically, without changing their address.  Therefore, the
routing protocol must support completely unstructured address
space.  RPL is specifically made for mobile ad-hoc networks, with
no assumptions on topologically aligned addressing.
Modularity: To keep the initial implementation small, yet allow
later for more complex methods, it is highly desirable that the
routing protocol has a simple base functionality, but can import
new functional modules if needed.  RPL has this property with the
concept of "objective function", which is a plugin to modify
routing behavior.
Extensibility: Since the Autonomic Networking Infrastructure is a
new concept, it is likely that changes in the way of operation
will happen over time.  RPL allows for new objective functions to
be introduced later, which allow changes to the way the routing
protocol creates the DAGs.
Multi-topology support: It may become necessary in the future to
support more than one DODAG for different purposes, using
different objective functions.  RPL allow for the creation of
several parallel DODAGs, should this be required.  This could be
used to create different topologies to reach different roots.
No need for path optimisation: RPL does not necessarily compute
the optimal path between any two nodes.  However, the ACP does not
require this today, since it carries mainly non-delay-sensitive
feedback loops.  It is possible that different optimisation
schemes become necessary in the future, but RPL can be expanded
(see point "Extensibility" above).
The need to potentially have multiple of these security associations
even temporarily run in parallel to determine which of them works
best does not support the most lightweight implementation options.
The simple policy of letting one side (Alice) decide what is best may
not lead to the mutual best result.
The two limitations can easier be solved if the solution was more
modular and as few as possible initial secure channel negotiation
protocols would be used, and these protocols would then take on the
responsibility to support more flexible objectives to negotiate the
mutually preferred ACP security channel protocol.
Consider the simple case where the use of native IPsec vs. IPsec via
GRE is to be negotiated and the objective is the maximum throughput.
Both sides would indicate some agreed upon performance metric and the
preferred encapsulation is the one with the higher performance of the
slower side.  IKEv2 does not support negotiation with this objective.
Consider dTLS and some form of 802.1AE (MACSEC) are to be added as
negotiation options - and the performance objective should work
across all IPsec, dDTLS and 802.1AE options.  In the case of MacSEC,
the negotiation would also need to determine a key for the peering.
It is unclear if it would be even appropriate to consider extending
the scope of negotiation in IKEv2 to those cases.  Even if feasible
to define, it is unclear if implementations of IKEv2 would be eager
to adopt those type of extension given the long cycles of security
testing that necessarily goes along with core security protocols such
as IKEv2 implementations.
To explicitly allow negotiation of the ACP channel protocol, GRASP
over a TLS connection using the GRASP_LISTEN_PORT and the nodes and
peers link-local IPv6 address is used.  When Alice and Bob support
GRASP negotiation, they do prefer it over any other non-explicitly
negotiated security association protocol and should wait trying any
non-negotiated ACP channel protocol until after it is clear that
GRASP/TLS will not work to the peer.