Patent Description:
A computer network is a collection of interconnected computing devices that can exchange data and share resources. Example network devices include switches or other layer two ("L2") devices that operate within the second layer of the Open Systems Interconnection ("OSI") reference model, i.e., the data link layer, and routers or other layer three ("L3") devices that operate within the third layer of the OSI reference model, i.e., the network layer. Common L3 operations include those performed in accordance with L3 protocols, such as the Internet protocol ("IP"). Network devices within computer networks often include a control unit that provides control plane functionality for the network device and forwarding units for routing or switching data units.

In an L3 network, network devices may use a Neighbor Discovery Protocol (NDP) to discover the presence of other network devices and link layer addresses, and to maintain reachability information about paths to active neighbors. For example, devices that implement NDP send or receive five types of neighbor discovery messages: router solicitation (RS), router advertisement (RA), neighbor solicitation (NS), neighbor advertisement (NA), and redirect. In some examples, NDP may be extended to include security extensions, such as SEcure Neighbor Discovery (SEND). SEND provides cryptographic mechanisms for network devices to secure delivery and authentication of neighbor discovery messages. As one example, a sender device originates a nonce, stores the nonce, and sends a neighbor discovery request message, e.g., neighbor solicitation message, including the nonce to prevent replay attacks. If the sender device receives a neighbor discovery response message, e.g., neighbor advertisement message, including the nonce that matches the nonce stored by the sender device, the sender device determines that the neighbor discovery response message is not a replay attack and learns the link layer addresses. If the neighbor discovery response message does not include a nonce that matches the nonce stored by the sender device, the sender device drops the neighbor discovery response message.

Cited art includes:
<NPL>.

Any embodiments or examples of the following description which are not within the scope of the appended claims are provided for illustrative purposes. In general, techniques are described for providing security extensions to neighbor discovery in Ethernet Virtual Private Network (EVPN). For example, network devices send and receive neighbor discovery message, e.g., using Neighbor Discovery Protocol (NDP), to discover the presence of neighboring devices and link layer addresses, and to maintain reachability information about the paths to active neighbors. In some examples, NDP is extended to include security extensions, such as SEcure
Neighbor Discovery (SEND). Using SEND, network devices generate neighbor discovery messages that carry public key-based signatures for securing and authenticating the neighbor discovery messages. For example, network devices include a nonce in neighbor discovery messages to prevent replay attacks. In the examples described herein, network devices are configured to process a received neighbor discovery response message even though the receiving network device did not originate the nonce.

In one example in which a host device is multi-homed to a plurality of network devices, e.g., Provider Edge (PE) devices, of an Ethernet segment in a collapsed IP fabric, the host device may, in response to receiving a neighbor discovery request message, e.g., neighbor solicitation message, including a nonce from a first PE device, send a neighbor advertisement message including the nonce to a second PE device of the Ethernet segment. That is, the first PE device may send the neighbor solicitation message with a nonce, but the second PE device receives the neighbor advertisement message with the nonce originated by the first PE device. Rather than dropping the neighbor advertisement message because the second PE device is unable to validate the nonce in the neighbor advertisement message due to the second PE device not having originated the nonce, the second PE device may be configured to relax the nonce validation requirement for neighbor discovery messages arriving on an Ethernet Segment Identifier (ESI) interface for the first and second PE devices coupled to the multi-homed host device. For example, the first PE device and second PE device may each be configured to determine whether a neighbor advertisement message arrives on the ESI interface connected to the host, and if so, the PE device may drop the nonce from the neighbor advertisement message even if the receiving PE device did not originate the nonce.

In another example in which a host device is multi-homed to a plurality of PE devices in a non-collapsed IP fabric, the sender device may send a neighbor discovery request message, e.g., neighbor solicitation message, including a nonce, where the source address of the neighbor solicitation message specifies a physical IP address of the sender device rather than the virtual (or anycast) IP address of an Integrated Routing and Bridging (IRB) interface to cause the neighbor advertisement message to be forwarded to the sender device that originated the neighbor solicitation message including the nonce.

In another example in which network devices may operate as a proxy for neighbor discovery (referred to herein as "EVPN-proxy"), as described in <NPL>. In this example, PE devices may intercept (i.e., "snooping") a first neighbor discovery response message, e.g., first neighbor advertisement message, including a nonce, that is sent from a local host device to a remote host device in response to a first neighbor discovery request message, e.g., neighbor solicitation message, from the remote host device. In response to determining that the PE device did not originate the nonce of the first neighbor advertisement message, the PE device drops the first neighbor advertisement message and sends a second neighbor solicitation message including the nonce to the local host device. The PE device may receive a second neighbor advertisement message including the nonce, store the learned link layer addresses, and
advertise the learned addresses to remote PE devices over the EVPN core. In this way, PE devices may act as a proxy by using the learned addresses to reply to neighbor discovery request message of local host devices rather than sending the neighbor discovery request message over the EVPN core.

In one example, a method includes receiving, by a first network device that implements Ethernet Virtual Private Network (EVPN), a neighbor discovery response message including a nonce originated by a second network device and not originated by the first network device. The method also includes processing, by the first network device, the neighbor discovery response message including the nonce originated by the second network device and not originated by the first network device.

In another example, a first network device that implements Ethernet Virtual Private Network (EVPN), comprising: one or more processors coupled to a memory, wherein the one or more processors are configured to: receive a neighbor discovery response message including a nonce originated by a second network device and not originated by the first network device; and process the neighbor discovery response message including the nonce originated by the second network device and not originated by the first network device.

In yet another example, a non-transitory computer-readable storage medium comprising instructions for causing one or more programmable processors of a network device to: receive a neighbor discovery response message including a nonce originated by a second network device and not originated by the first network device; and process the neighbor discovery response message including the nonce originated by the second network device and not originated by the first network device.

The details of one or more aspects of the techniques are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques of this disclosure will be apparent from the description and drawings, and from the claims.

<FIG> is a block diagram illustrating a network system <NUM> configured to provide security extensions, e.g., Secure Neighbor Discovery (SEND), to neighbor discovery in EVPN in a collapsed IP fabric, in accordance with one or more aspects of the techniques described in this disclosure. <FIG> illustrates an example network system <NUM> including a data center <NUM> connected to customer devices <NUM>. Data center <NUM> may, for example, host infrastructure equipment, such as networking and storage systems, redundant power supplies, and environmental controls. In general, data center <NUM> provides an operating environment for applications and services for customer devices <NUM> coupled to the data center, e.g., by a service provider network (not shown). In some examples, a service provider network that couples customer devices <NUM> to data center <NUM> may be coupled to one or more networks administered by other providers, and may thus form part of a large-scale public network infrastructure, e.g., the Internet.

In some examples, data center <NUM> represents one of many geographically distributed network data centers. As illustrated in the example of <FIG>, data center <NUM> may be a facility that provides network services for customers through customer devices <NUM>. Customer devices <NUM> may include the devices of entities (such as enterprises and governments) and of individuals. For example, a network data center may host web services for both enterprises and end users. Other example services may include data storage, virtual private networks, traffic engineering, file service, data mining, scientific- or super-computing, and so on. In some examples, data center <NUM> may be individual network servers, network peers, or otherwise. In some examples, data center <NUM> is an enterprise or internal data center.

Data center <NUM> may include one or more interconnected servers, e.g., servers 11A-11N (collectively, "servers <NUM>") that each provides execution and storage environments for applications and data associated with customers via customer devices <NUM> and may be physical servers, virtual machines, or combinations thereof. Servers <NUM> are interconnected via an Internet Protocol (IP) fabric <NUM>, which may comprise a fabric provided by one or more tiers of physical network devices, such as, for example, routers, gateways, switches, hubs, modems, bridges, repeaters, multiplexers, servers, virtual machines running on one or more of the same, and other example network devices. Servers <NUM> may be referred to herein as "hosts.

IP fabric <NUM> may provide servers <NUM> with redundant (multi-homed) connectivity to the IP fabric and service provider network. In this example, IP fabric <NUM> represents layer two (L2) and layer three (L3) switching and routing components that provide point-to-point connectivity between servers <NUM>. In one example, IP fabric <NUM> comprises a set of interconnected, packet-based routers and switches that implement various protocols. In one example, IP fabric <NUM> may comprise devices that provide IP point-to-point connectivity. In some multi-staged networks such as IP fabric <NUM>, each switch resides in a defined layer of the network, referred to as a CLOS topology or a spine and leaf network. As shown in the example of <FIG>, spine devices 14A and 14B (collectively, "spine devices <NUM>") reside in a first, top layer and leaf devices 10A-10N (collectively, "leaf devices <NUM>") reside in a second layer. Leaf devices <NUM> may be network devices (e.g., Top-of-Rack (TOR) switches) that provide layer <NUM> (e.g., MAC) and/or layer <NUM> (e.g., IP) routing and/or switching functionality. Spine devices <NUM> aggregate traffic flows and provides high-speed connectivity between leaf devices <NUM>. In some examples, data center <NUM> may deploy EVPN-VXLAN over a physical underlay network in which IP fabric <NUM> is collapsed into a single layer of leaf devices <NUM> (referred to herein as "collapsed IP fabric"). In a collapsed IP fabric, leaf devices <NUM> serve as both Layer <NUM> and Layer <NUM> gateways. Spine devices <NUM> of the collapsed IP fabric provide only Layer <NUM> routing functionality. Spine devices <NUM> and leaf devices <NUM> may each include one or more processors and a memory, and that are capable of executing one or more software processes. As shown in the example of <FIG>, each of spine devices <NUM> is communicatively coupled to each of leaf devices 10A-10N, and servers <NUM> are directly connected to leaf devices <NUM> that operate as both L2 and L3 gateways, and is thus arranged as a collapsed IP fabric. The configuration of network system <NUM> illustrated in <FIG> is merely an example. For example, data center <NUM> may include any number of spine and leaf devices, and IP fabric <NUM> may be arranged as a non-collapsed IP fabric (as further described below in the example of <FIG>).

Spine devices <NUM> and leaf devices <NUM> may each participate in an L2 virtual private network ("L2VPN") service, such as an Ethernet Virtual Private Network (EVPN). An EVPN is a service that provides a form of L2 connectivity across an intermediate L3 network, such as a service provider network, to interconnect two or more L2 networks that may be located in different racks of data center <NUM>. Often, EVPN is transparent to the customer networks in that these customer networks are not aware of the intervening intermediate network and instead act and operate as if these customer networks were directly connected and form a single L2 network. In a way, EVPN enables a form of transparent local area network ("LAN") connection between two customer networks (e.g., different racks of data center <NUM>) that each operates an L2 network and may also be referred to as a "transparent LAN service.

To provide flexibility and scalability, multiple bridge domains can be defined for a particular EVPN instance (EVI). One or more EVIs can be associated with a single L3 VPN virtual routing and forwarding instance (VRF). For example, each data center tenant may be assigned a unique VRF; a tenant can encompass one or more EVPN instances and one or more bridge domains (e.g., VLANs or VXLANs) per EVPN instance. Spine devices <NUM> and leaf devices <NUM> may be included in one or more virtual LANs (VLANs), which are groups of devices on one or more LANs that are configured to communicate as if they are attached to the same wire.

As shown in <FIG>, each of servers <NUM> is multi-homed to leaf devices <NUM> by Ethernet segments for redundancy, load balancing, or both. As one example, server 11A is multi-homed to leaf devices 10A and 10B by Ethernet segment <NUM>. Ports of leaf devices 10A and 10B (e.g., TOR switches) are configured as logically bundled Ethernet segment <NUM> such that leaf devices 10A and 10B operate to provide either single-active or active-active multi-homed L2 connectivity to server 11A of data center <NUM>.

To enable leaf devices 10A and 10B connected to the same Ethernet segment <NUM> to automatically discover one another, each of leaf devices 10A and 10B advertises an Ethernet segment route (Type <NUM>), which is typically unique across all EVPN instances (EVIs), for each of the Ethernet segments multi-homed by the leaf device. For example, each of leaf devices 10A and 10B use Border Gateway Protocol (BGP) to advertise an Ethernet segment route that includes a Route Distinguisher (RD), ESI, and an originating network device's network address (e.g., IP address).

In addition, for each EVI, the EVPN protocol directs the router to output a routing protocol message advertising an Ethernet Auto-Discovery (AD) route (Type <NUM>) specifying the relevant ESI for the Ethernet segment coupled to the EVPN instance. That is, each of leaf devices 10A and 10B may advertise an Ethernet AD route per Ethernet segment to advertise reachability of the leaf device for the Ethernet segment. For example, each of leaf devices 10A and 10B, for each EVI, use BGP to advertise an Ethernet AD route that includes an RD (which may include, e.g., an IP address of the originating PE device), ESI, Ethernet Tag Identifier, and VNI. Each of the routes are advertised and imported by all multi-homed leaf devices that share the same EVI on the advertising ESI. In the example of <FIG>, each of leaf devices 10A and 10B of the EVPN instance advertise and import the routes described above to discover each other for Ethernet segment <NUM>.

Although additional network devices are not shown for ease of explanation, it should be understood that network system <NUM> may comprise additional network and/or computing devices such as, for example, one or more additional switches, routers, hubs, gateways, security devices such as firewalls, intrusion detection, and/or intrusion prevention devices, servers, computer terminals, laptops, printers, databases, wireless mobile devices such as cellular phones or personal digital assistants, wireless access points, bridges, cable modems, application accelerators, or other network devices. The configuration of network system <NUM> illustrated in <FIG> is merely an example.

In some examples, network devices may implement neighbor discovery protocols to discover neighboring devices. For example, hosts, such as servers <NUM> may implement Neighbor Discovery Protocol (NDP) to send and receive neighbor discovery messages to find neighboring devices, such as leaf devices <NUM>, that may forward packets on their behalf. Network devices use NDP to determine the link layer addresses for neighbors known to reside on attached links. Network devices that use NDP may maintain reachability information about the paths to active neighbors, such as by actively keeping track of which neighbors are reachable and which are not, and to detect changes in link layer addresses.

NDP defines five different Neighbor Discovery messages. For example, NDP defines Internet Control Message Protocol (ICMP) messages including, for example, router solicitation (RS) messages, router advertisement (RA) messages, neighbor solicitation (NS) messages, neighbor advertisement (NA) messages, and redirect messages.

When an interface of a host becomes enabled, the host may send a router solicitation message that requests routers to generate router advertisements. Routers may send router advertisement messages to advertise their presence and with various links and Internet parameters. Router advertisement messages contain prefixes that are used for determining whether another address shares the same link and/or address configuration, a suggested hop limit value, etc..

A network device may send a neighbor discovery request message, e.g., neighbor solicitation message, to request the link layer address of a neighbor and may also provide its own link layer address to the target network device. Network devices may also use the neighbor solicitation message to verify that a neighbor is still reachable via a cached link layer address. The link layer address may be a link layer identifier for an interface to a link (e.g., IEEE <NUM> addresses for Ethernet links).

In response to receiving a neighbor solicitation message, a network device may send a neighbor discovery response message, e.g., neighbor advertisement message. The neighbor advertisement message may include, for example, a link layer address that the network device (e.g., endpoint <NUM>) has learned. In some examples, a network device may send a neighbor advertisement message to announce a change in a link layer address. Routers may send a redirect message to inform hosts to redirect traffic to the destination (e.g., to a different next hop).

An NDP message may include an NDP message header (e.g., ICMPv6 header and neighbor discovery message-specific data) and zero or more NDP options (e.g., Source Link Layer Address, Target Link Layer Address, Prefix Information, Redirected Header, and Maximum Transmission Unit (MTU)) included in the Type-Length-Value (TLV) of the NDP message. Additional examples of NDP message are described in <NPL>.

In some examples, NDP may be extended with security extensions, such as SEcure Neighbor Discovery (SEND). For example, network devices may use SEND to establish certification paths, use Cryptographically Generated Addresses (CGA), use public key signatures (e.g., Rivest-Shamir-Adleman (RSA) signatures), and/or use a timestamp and/or nonce as an NDP option. In the examples described herein, network devices of network system <NUM> may use nonce as an NDP option.

Network devices may use a nonce as an NDP option for the NDP message to prevent replay attacks. A nonce is an unpredictable random or pseudo-random number generated by a device and used exactly once. The nonce is used to assure that a particular advertisement is linked to the solicitation that triggered it. For example, a sender device may send a neighbor solicitation message including a nonce and stores the nonce such that the sender device can recognize any responses (e.g., neighbor advertisement messages) containing the nonce. The target network device receives the neighbor solicitation message including the nonce, and in response, sends a neighbor advertisement message including the nonce copied from the neighbor solicitation message. By including the nonce in the neighbor advertisement message, the sender device determines whether the neighbor advertisement message is a fresh response to the neighbor solicitation message sent earlier by the sender device. For example, the sender device may compare the stored nonce and the nonce included in the neighbor advertisement message. If the nonce is the same, the sender device determines that the neighbor advertisement message is the response to the neighbor solicitation message that was sent earlier by the sender device. If the nonce of the neighbor solicitation message does not match the nonce stored in the receiver device, the receiver device discards the neighbor solicitation message. Additional examples of SEND are described in <NPL>.

In some examples, the network devices that exchange neighbor discovery messages may be multi-homed in a collapsed IP fabric as described above. For example, a host, such as server 11A, may be directly connected and multi-homed to leaf devices 10A and 10B. In these examples, the sender device, e.g., leaf device 10A, may send a neighbor solicitation message including a nonce to server 11A. Server 11A may in some instances send a neighbor advertisement message with the nonce originated by leaf device 10A to leaf device 10B instead. That is, in the case of network devices configured in a multi-homed Ethernet segment, there may in some instances be an asymmetric request and response path where the sender device of the Ethernet segment sends the Neighbor Solicitation message including a nonce and the other network device of the Ethernet segment receives a Neighbor Advertisement message including the nonce originated by the sender device. For example, server 11A may load-balance the neighbor advertisement message on any of the links to leaf devices 10A and 10B. Ordinarily, without the techniques of this disclosure, a receiving leaf device that receives a neighbor advertisement message including a nonce that was not originated by the receiving leaf device would discard the neighbor advertisement message (and therefore not learn the link layer addresses of the target host).

In accordance with the techniques of this disclosure, the devices of network system <NUM> may provide security extensions, e.g., SEND, to neighbor discovery in EVPN. As described above, devices of network system <NUM> are arranged in a collapsed IP fabric. For example, servers <NUM> are directly connected and multi-homed to leaf devices <NUM> (e.g., TOR switches) that operate as L2 and L3 gateways. In a collapsed IP fabric, a receiving device, e.g., leaf device 10B, that receives a neighbor advertisement message including a nonce originated by another device, e.g., leaf device 10A, belonging to the same ESI, may be configured to relax the nonce validation requirement, i.e., that the nonce included in a received neighbor advertisement message must match the nonce stored in the receiving device.

In the example of <FIG>, leaf devices 10A and 10B belong to the same ESI of Ethernet segment <NUM>. In this example, leaf device 10A may send a neighbor solicitation message <NUM> including a nonce on a link directly attached to leaf device 10A and server 11A. Server 11A responds to the neighbor solicitation message <NUM> with a neighbor advertisement message <NUM> including the nonce from neighbor solicitation message <NUM>. Server 11A may load balance the neighbor advertisement message <NUM> on the links of Ethernet segment <NUM>, and in some instances, send neighbor advertisement message <NUM> to leaf device 10B.

In response to receiving neighbor advertisement message <NUM> including the nonce originated by leaf device 10A, leaf device 10B determines that leaf device 10B did not originate the nonce. For example, leaf device 10B may determine that the nonce included in the neighbor advertisement message <NUM> does not match a nonce stored in leaf device 10B because leaf device 10B did not originate the nonce. Rather than drop neighbor advertisement message <NUM>, leaf device 10B is configured to relax the requirement that the nonce included in neighbor advertisement message <NUM> must match the nonce stored in leaf device 10B. For example, leaf device 10B is configured to determine whether a neighbor advertisement message <NUM> arrives on the ESI interface connected to server 11A, and if so, leaf device 10B may drop the nonce from neighbor advertisement message <NUM> even though leaf device 10B did not originate the nonce. In the example of <FIG>, leaf device 10B may determine that neighbor advertisement message <NUM> is received on the ESI interface connected to server 11A. In response, leaf device 10B may drop the nonce and learn the link layer address of server 11A included in neighbor advertisement message <NUM>.

In some examples, leaf device 10B may include an option to be configured to relax the nonce validation requirement through a management interface (e.g., command-line interface (CLI)). In some examples, the configuration to relax the nonce validation requirement may be "switched off' via configuration changes through the management interface.

<FIG> is a flowchart illustrating an example operation of the network system <NUM> in <FIG> configured to provide security extensions, e.g., SEND, to neighbor discovery in EVPN for a collapsed IP fabric, in accordance with one or more aspects of the techniques described in this disclosure. As described above, devices of network system <NUM> are arranged in a collapsed IP fabric where leaf devices <NUM> serve as both Layer <NUM> and Layer <NUM> gateways, and spine devices <NUM> provide only Layer <NUM> routing functionality.

In the example of <FIG>, leaf device 10A sends a neighbor discovery request message, e.g., neighbor solicitation message <NUM>, including a nonce originated by leaf device 10A (<NUM>). Server 11A receives neighbor solicitation message <NUM> (<NUM>) and generates a neighbor discovery response message, e.g., neighbor advertisement message <NUM>, including the nonce originated by leaf device 10A (<NUM>). For example, in response to receiving neighbor solicitation message <NUM>, server 11A generates a neighbor advertisement message <NUM> including the nonce copied from neighbor solicitation message <NUM>.

Server 11A sends the neighbor discovery response message, e.g., neighbor advertisement message <NUM>, including the nonce copied from the neighbor solicitation message <NUM>. In some examples, server 11A load balances the neighbor advertisement message <NUM> on the Ethernet segment (<NUM>), which results in leaf device 10B of Ethernet segment <NUM> receiving the neighbor advertisement message <NUM> including the nonce originated by leaf device 10A (<NUM>). In accordance with the techniques described in this disclosure, leaf device 10B processes neighbor advertisement message <NUM> even though leaf device 10B did not originate the nonce. For example, leaf device 10B determines whether the nonce included in neighbor advertisement message <NUM> is originated by leaf device 10B (<NUM>). More specifically, leaf device 10B determines whether the nonce included in neighbor advertisement message <NUM> matches a nonce stored in leaf device 10B (if leaf device 10B originated the neighbor solicitation message). In this example, since leaf device 10B did not originate the nonce and thus does not store a nonce, leaf device 10B determines that the nonce included in neighbor advertisement message <NUM> does not match a nonce stored in leaf device 10B (<NUM>).

Rather than drop neighbor advertisement message <NUM>, leaf device 10B relaxes the nonce validation requirement. For example, in response to determining that the nonce is not originated by leaf device 10B, leaf device 10B determines whether neighbor advertisement message <NUM> was received on an ESI interface for Ethernet segment <NUM> (<NUM>). For example, leaf device 10B determines whether leaf device 10B belongs to an ESI (e.g., by advertising Ethernet Segment routes (Type <NUM>)) of Ethernet segment <NUM> connecting leaf devices 10A and 10B. Leaf device 10B may determine that neighbor advertisement message <NUM> was received on an ESI interface for Ethernet segment <NUM>, and drops the nonce from neighbor advertisement message <NUM> to learn a link layer address from neighbor advertisement message <NUM> (<NUM>).

<FIG> is a block diagram illustrating another example network system <NUM> configured to provide security extensions, e.g., SEND, to neighbor discovery in EVPN for a non-collapsed IP fabric, in accordance with one or more aspects of the techniques described in this disclosure. In the example of <FIG>, the physical underlay network over which EVPN-VXLAN is deployed is a two-layer IP fabric, which may include spine devices <NUM> and leaf devices <NUM>. Spine devices <NUM> provide connectivity between leaf devices <NUM>, and leaf devices <NUM> provide connectivity to attached hosts, e.g., servers <NUM>. In the overlay network, leaf devices <NUM> function as L2 gateways that handle traffic within a VXLAN, and spine devices <NUM> function as L3 gateways that handle traffic between VXLANs through the use of Integrated Routing and Bridging (IRB). In the example of <FIG>, servers <NUM> access data center <NUM> via intermediate switches 18A-18N. In the example of <FIG>, intermediate switch 18A is multi-homed to leaf devices <NUM> by Ethernet segment <NUM>. In this example, IP fabric <NUM> is referred to as a "non-collapsed IP fabric.

In some examples, network devices, such as leaf devices <NUM> and servers <NUM>, exchange neighbor discovery messages via intermediate switches <NUM>. In this example, intermediate device 18A is multi-homed to leaf devices 10A and 10B, each functioning as an L3 gateway in a non-collapsed IP fabric as described above. In these examples, the sender device, leaf device 10A, may send a neighbor discovery request message, e.g., neighbor solicitation message <NUM>, including a nonce to intermediate switch 18A, which switches the neighbor solicitation message <NUM> to server 11A. Server 11A responds to the neighbor solicitation message <NUM> with a neighbor discovery response message, e.g., neighbor advertisement message <NUM>, including the nonce from neighbor solicitation message <NUM>. Server 11A may send the neighbor advertisement message <NUM> to intermediate switch 18A, which load balances the neighbor advertisement message <NUM> on any of the links of Ethernet segment <NUM>, and in some instances, send neighbor advertisement message <NUM> to leaf device 10B. That is, in the case of network devices configured in a multi-homed Ethernet segment, there may in some instances be an asymmetric request and response path where the sender device of the Ethernet segment sends the neighbor solicitation message including a nonce and the other network device of the Ethernet segment receives a neighbor advertisement message including the nonce originated by the sender device.

In these examples in which network devices exchange neighbor discovery messages in a non-collapsed IP fabric via an intermediate switch, the network devices are unable to relax the nonce validation requirement (e.g., as described in the example of <FIG>) because an attacker may learn the source address of the sender device and use the source address to perform a replay attack on the network device that receives the neighbor advertisement message (e.g., leaf device 10B). For example, without the techniques described in this disclosure, a sender device typically sends a neighbor solicitation message with a source address of an address assigned to an interface from which the neighbor solicitation message is sent. In the example in which a sender device implements an IRB interface, the sender device sends a neighbor solicitation message including a source address that specifies the address assigned to the IRB interface (e.g., a virtual or anycast IP address). However, in a non-collapsed IP fabric such as in the example shown in <FIG>, an attacker may learn the virtual IP address of the IRB interface of the sender device and may use the virtual IP address to perform a replay attack on the network device that receives the neighbor advertisement message (e.g., leaf device 10B).

In accordance with the techniques described in this disclosure, the devices of network system <NUM> may send a neighbor discovery request message, e.g., neighbor solicitation message, including a nonce and a source address that specifies a physical IP address of the sender device to cause the neighbor advertisement message to be forwarded to the sender device that originated the nonce.

As described above, devices of network system <NUM> are arranged in a non-collapsed IP fabric. In a non-collapsed IP fabric, a sender device, e.g., leaf device 10A, may send a neighbor discovery request message, e.g., neighbor solicitation message <NUM>, including a nonce and a source address of the neighbor solicitation message specifying a physical IP address of leaf device 10A rather than the virtual IP address of the IRB interface.

In the example of <FIG>, leaf device 10A may send a neighbor solicitation message <NUM> including a nonce to request the link layer address of a neighboring device, e.g., server 11A, and a source address of neighbor solicitation message <NUM> that specifies a physical IP address of leaf device 10A. In some examples, leaf device 10A may include an option to be configured to specify a physical IP address of the device as a source address of a neighbor solicitation message through a management interface (e.g., command-line interface (CLI)). In some examples, the configuration to specify the physical IP address as the source address may be "switched off' via configuration changes through the management interface, and use the virtual IP address of the IRB interface.

Intermediate switch 18A receives the neighbor solicitation message <NUM> and switches the neighbor solicitation message <NUM> to server 11A. Server 11A receives the neighbor solicitation message <NUM> and responds with a neighbor discovery response message, e.g., neighbor advertisement message <NUM>, including the nonce from the neighbor solicitation message <NUM>, and a destination address of neighbor advertisement message <NUM> that specifies the physical IP address of leaf device 10A. Server 11A may send neighbor advertisement message <NUM> to intermediate switch 18A, which load balances the neighbor advertisement message <NUM> on any of the links of Ethernet segment <NUM>, and in some instances, send the neighbor advertisement message <NUM> to leaf device 10B. Leaf device 10B receives neighbor advertisement message <NUM> including the nonce originated by leaf device 10A, and in this example, leaf device 10B may determine that the destination address specifies the physical IP address of leaf device 10A, which causes leaf device 10B to send the neighbor solicitation message <NUM> over the overlay network, e.g., VXLAN, toward leaf device 10A. In this way, by specifying the physical IP address of leaf device 10A as the source address of neighbor solicitation message <NUM>, server 11A may specify the physical IP address of leaf device 10A as the destination address of neighbor advertisement message <NUM> to cause a network device receiving neighbor advertisement message <NUM> to be forwarded to leaf device 10A that originated the nonce.

The example described in <FIG> is also applicable to a collapsed IP fabric, as described in the example of <FIG>. That is, in either a collapsed or non-collapsed IP fabric, the sender device, e.g., leaf device 10A, may a send neighbor solicitation message including a nonce, where the neighbor solicitation message includes a source address specifying a physical IP address of leaf device 10A, to cause the neighbor advertisement message to be forwarded to the sender device that originated the nonce.

<FIG> is a flowchart illustrating an example operation of the network system <NUM> in <FIG> configured to provide security extensions, e.g., SEND, to neighbor discovery in EVPN in a non-collapsed IP fabric, in accordance with one or more aspects of the techniques described in this disclosure. As described above, devices of network system <NUM> are arranged in a non-collapsed IP fabric.

In the example of <FIG>, leaf device 10A may send a neighbor discovery request message, e.g., neighbor solicitation message <NUM>, including a nonce and a source address of neighbor solicitation message <NUM> that specifies a physical IP address of leaf device 10A (<NUM>). For example, rather than specifying a source address of the neighbor solicitation message as the address assigned to the IRB interface (e.g., a virtual or anycast IP address), leaf device 10A specifies the source address of neighbor solicitation message <NUM> as the physical IP address of leaf device 10A.

An intermediate device, e.g., intermediate switch 18A, receives the neighbor solicitation message <NUM> (<NUM>) and switches the neighbor solicitation message <NUM> to server 11A (<NUM>). Server 11A receives the neighbor solicitation message <NUM> (<NUM>) and generates a neighbor discovery response message, e.g., neighbor advertisement message <NUM>, including the nonce and a destination address of neighbor advertisement message <NUM> specifying the physical IP address of leaf device 10A (<NUM>). For example, server 11A responds with neighbor advertisement message <NUM> including the nonce copied from neighbor solicitation message <NUM>. Server 11A also uses the physical IP address of leaf device 10A that is specified in the source address of neighbor solicitation message <NUM> as the destination address of neighbor advertisement message <NUM>.

Server 11A sends neighbor advertisement message <NUM> to intermediate switch 18A (<NUM>). Intermediate switch 18A receives neighbor advertisement message <NUM> (<NUM>) and load balances neighbor advertisement message <NUM> on the links of Ethernet segment <NUM>, and in some instances, sends neighbor advertisement message <NUM> to leaf device 10B (<NUM>).

Leaf device 10B receives neighbor advertisement message <NUM> including the nonce originated by leaf device 10A (<NUM>), and in this example, leaf device 10B processes neighbor advertisement message <NUM> even though leaf device 10B did not originate the nonce. For example, leaf device 10B determines that the destination address of neighbor advertisement message <NUM> specifies the physical IP address of leaf device 10A (<NUM>), which causes leaf device 10B to send neighbor solicitation message <NUM> over the overlay network, e.g., VXLAN, toward leaf device 10A (<NUM>).

<FIG> is a block diagram illustrating another example network system <NUM> configured to provide security extensions, e.g., SEND, to a neighbor discovery protocol in EVPN for a network device operating as a proxy for neighbor discovery, in accordance with one or more aspects of the techniques described in this disclosure.

In the example of <FIG>, network system <NUM> includes intermediate network <NUM> to interconnect a plurality of edge networks, e.g., customer networks 506A-506C (collectively, "customer networks <NUM>"). Intermediate network <NUM> is a Layer <NUM> network that natively supports L3 operations including those performed in accordance with L3 protocols, such as the Internet protocol ("IP"). L3 is also known as a "network layer" in the OSI model and the "IP layer" in the TCP/IP model, and the term L3 may be used interchangeably with "network layer" and "IP" throughout this disclosure. As a result, intermediate network <NUM> may be referred to herein as a Service Provider ("SP") network or, alternatively, as a "core network" considering that intermediate network <NUM> acts as a core to interconnect edge networks, such as customer networks <NUM>. Intermediate network <NUM> represents an L2/L3 switch fabric for one or more customer networks that may implement an EVPN service. As described above, EVPN is a service that provides a form of L2 connectivity across an intermediate L3 network, such as intermediate network <NUM>, to interconnect two or more L2 customer networks, such as L2 customer networks <NUM>, that may be located in different geographical areas (in the case of service provider network implementation) and/or in different racks (in the case of a data center implementation).

Customer networks <NUM> have customer endpoints 504A-504C (collectively, "endpoints <NUM>"), respectively, that provide computing environments for subscribers / customers. Each of endpoints <NUM> may represent one or more non-edge switches, routers, hubs, gateways, security devices such as firewalls, intrusion detection, and/or intrusion prevention devices, servers, computer terminals, laptops, printers, databases, wireless mobile devices such as cellular phones or personal digital assistants, wireless access points, bridges, cable modems, application accelerators, or other network devices. Endpoints <NUM> may access intermediate network <NUM> via one or more provider edge (PE) devices 510A and 510B (collectively, "PE devices <NUM>"). PE devices <NUM> may each represent a router, switch, or other suitable network device that participates in an L2VPN service, such as an EVPN. As described above, EVPN is a service that provides a form of L2 connectivity across an intermediate L3 network, e.g., intermediate network <NUM>, to interconnect two L2 customer networks, such as L2 customer networks <NUM>, that are usually located in two different geographic areas. In the example of <FIG>, intermediate network <NUM> may be referred to as an "EVPN core.

In the example of <FIG>, PE devices <NUM> may operate as a proxy for neighbor discovery to reduce the flooding of neighbor discovery messages over an EVPN core (referred to herein as "EVPN-proxy"). For example, endpoints <NUM> may send neighbor discovery messages via PE devices <NUM>. In this example, endpoint 504A may send a neighbor solicitation message including a link layer address of endpoint 504A to PE device 510A, which sends the neighbor solicitation message over the EVPN core, e.g., intermediate network <NUM>, to PE device 510B, which in turn sends the neighbor solicitation message to a local host, e.g., endpoint 504B. In response, endpoint 504B sends a neighbor advertisement message including a local link layer address and is destined for endpoint 504A. By implementing EVPN-proxy, PE device 510B may intercept (i.e., "snoop") the neighbor advertisement message from endpoint 504B to learn the local link layer address of endpoint 504B, store the link layer address of endpoint 504B (e.g., in a proxy table), and advertise the locally learned link layer address using MAC/IP Advertisement route (Type <NUM>) over the EVPN core <NUM> to other PE devices. In these examples, PE device 510B may act as a proxy by using the learned link layer addresses to reply locally to neighbor discovery request messages, which reduces the flooding of neighbor discovery messages over the EVPN core. For instance, PE device 510B may receive a neighbor solicitation message from endpoint 504C to request a link layer address of endpoint 504A. Rather than send the neighbor solicitation message over the EVPN core <NUM>, PE device 510B may send a neighbor advertisement message including the link layer addresses learned from the neighbor advertisement message sent by endpoint 504B to endpoint 504A. Additional examples of EVPN-Proxy are described in <NPL>.

In some examples, endpoints <NUM> may send neighbor discovery messages including a nonce. Ordinarily, without the techniques described in this disclosure, PE devices <NUM> are unable to snoop neighbor advertisement messages because the PE devices <NUM> do not originate the nonce and discard the neighbor advertisement messages (and are therefore unable to learn the link layer addresses of local and remote host devices). Without snooping the neighbor advertisement messages, the PE devices are unable to learn local link layer addresses and cannot advertise locally learned link layer addresses to remote PE devices.

In accordance with the techniques described in this disclosure, PE devices <NUM> implementing EVPN-proxy may provide security extensions, e.g., SEND, to neighbor discovery, in EVPN. In the example of <FIG>, endpoint 504A may send a first neighbor discovery request message, e.g., neighbor solicitation message <NUM>, including a nonce to PE device 510A, which sends neighbor solicitation message <NUM> over the EVPN core, e.g., intermediate network <NUM>, to PE device 510B. PE device 510B sends neighbor solicitation message <NUM> to a local target destination device, e.g., endpoint 504B. In response, endpoint 504B sends a first neighbor discovery response message, e.g., neighbor advertisement message <NUM>, including the nonce and local link layer addresses of endpoints 504A and 504B.

PE device 510B intercepts neighbor advertisement message <NUM> and determines whether PE device 510B originated the nonce. In this example, PE device 510B determines that neighbor advertisement message <NUM> includes a nonce that is not stored in PE device 510B. In response, PE device 510B drops neighbor advertisement message <NUM>, and sends a new neighbor discovery request message, e.g., neighbor solicitation message <NUM>, including the nonce, to endpoint 504B. Endpoint 504B receives the new neighbor solicitation message <NUM> and responds with a second neighbor discovery response message, e.g., neighbor advertisement message <NUM>, including the nonce. PE device 510B receives neighbor advertisement message <NUM>, determines that neighbor advertisement message <NUM> includes the nonce, and stores the learned link layer addresses (e.g., for endpoints 504A and 504B) in a proxy table. PE device 510B advertises (e.g., using MAC/IP Advertisement route (Type <NUM>)) the learned link layer addresses for endpoint 504B over the EVPN core <NUM> to remote PE devices, e.g., PE device 510A. In this way, PE device 510B may act as a proxy by using the learned link layer addresses to reply to local neighbor discovery request messages rather than sending the neighbor discovery messages over the EVPN core. For example, when endpoint 504C sends neighbor solicitation message <NUM> from endpoint 504C to request a link layer address of endpoint 504A, PE device 510B does not send neighbor solicitation message <NUM> over EVPN core <NUM>, but instead replies locally to endpoint 504C by sending neighbor advertisement message <NUM> including the link layer addresses learned from neighbor advertisement message <NUM>, which reduces the flooding of neighbor discovery messages over the EVPN core.

In some examples, PE device 510B may include an option to be configured to operate as an EVPN-proxy for Neighbor Discovery messages through a management interface (e.g., command-line interface (CLI)). In some examples, the configuration to operate as an EVPN-proxy for Neighbor Discovery messages may be "switched off' via configuration changes through the management interface.

<FIG> is a flowchart illustrating an example operation of the network system <NUM> in <FIG> configured to provide security extensions, e.g., SEND, to a neighbor discovery protocol in EVPN for a network device operating as a proxy for neighbor discovery, in accordance with one or more aspects of the techniques described in this disclosure.

In the example of <FIG>, a sender device, e.g., endpoint 504A, sends a first neighbor discovery request message, e.g., neighbor solicitation message <NUM>, including a nonce (<NUM>). Endpoint 504A sends neighbor solicitation message <NUM> to PE device 510A, which sends neighbor solicitation message <NUM> over the EVPN core <NUM> to PE device 510B. PE device 510B then sends the neighbor solicitation message <NUM> to the target destination device, e.g., endpoint 504B. Endpoint 504B receives the neighbor solicitation message <NUM> (<NUM>) and sends a first neighbor discovery response message, e.g., neighbor advertisement message <NUM>, including the nonce originated by endpoint 504A (<NUM>). For example, in response to receiving neighbor solicitation message <NUM>, endpoint 504B generates neighbor advertisement message <NUM> including the nonce copied from neighbor solicitation message <NUM> and destined for endpoint 504A.

PE device 510B may intercept the first neighbor discovery response message, e.g., neighbor advertisement message <NUM> (<NUM>). PE device 510B processes neighbor advertisement message <NUM> even though PE device 510B did not originate the nonce. For example, PE device 510B determines whether the nonce included in neighbor advertisement message <NUM> intercepted from endpoint 504B is originated by endpoint 504A (<NUM>). More specifically, PE device 10B determines whether the nonce included in the neighbor advertisement message <NUM> matches a nonce stored in PE device 510B. In this example, since PE device 510B does not store the nonce, PE device 510B determines that the nonce included in neighbor advertisement message <NUM> does not match a nonce stored in PE device 510B.

PE device 510B drops the first neighbor advertisement message <NUM> (<NUM>) and sends a new neighbor discovery request message, e.g., neighbor solicitation message <NUM>, including the nonce (<NUM>). Endpoint 504B receives the new neighbor solicitation message <NUM> including the nonce (<NUM>). In response, endpoint 504B sends a second neighbor discovery response message, e.g., neighbor advertisement message <NUM>, including the nonce (<NUM>). PE device 510B receives the neighbor advertisement message <NUM> including the nonce (<NUM>). In response to determining that the nonce in neighbor advertisement message <NUM> matches the nonce in the neighbor solicitation message <NUM>, PE device 510B stores one or more link layer addresses learned from neighbor advertisement message <NUM> (<NUM>). In this way, when PE device 10B receives a third neighbor discovery request message, e.g., neighbor solicitation message <NUM>, from a local host device, e.g., endpoint 504C, PE device 510B may act as a proxy by using the learned link layer addresses to reply locally to endpoint 504C (e.g., neighbor advertisement message <NUM>) to reduce the flooding of neighbor discovery messages over an EVPN core, i.e., by not sending neighbor solicitation message <NUM> over an EVPN core (<NUM>).

<FIG> is a block diagram illustrating an example network device configured to provide SEcure Neighbor Discovery (SEND) in EVPN, in accordance with one or more aspects of the techniques described in this disclosure. Network device <NUM> is described with respect to any of leaf devices <NUM> of <FIG> and <FIG>, and PE devices <NUM> of <FIG>, but may be performed by any of the devices of <FIG>, <FIG>, and <FIG>.

As shown in <FIG>, network device <NUM> includes a control unit <NUM> having a routing component <NUM> (control plane), and control unit <NUM> that is coupled to forwarding component <NUM> (data plane). Forwarding component <NUM> is associated with one or more interface cards 740A-740N ("IFCs <NUM>") that receive packets via inbound links 742A-742N ("inbound links <NUM>") and send packets via outbound links 744A-744N ("outbound links <NUM>"). IFCs <NUM> are typically coupled to links <NUM>, <NUM> via a number of interface ports (not shown). Inbound links <NUM> and outbound links <NUM> may represent physical interfaces, logical interfaces, or some combination thereof.

Elements of control unit <NUM> and forwarding unit <NUM> may be implemented solely in software, or hardware, or may be implemented as combinations of software, hardware, or firmware. For example, control unit <NUM> may include one or more processors, one or more microprocessors, digital signal processors ("DSPs"), application specific integrated circuits ("ASICs"), field programmable gate arrays ("FPGAs"), or any other equivalent integrated or discrete logic circuitry, or any combination thereof, which execute software instructions. In that case, the various software modules of control unit <NUM> may comprise executable instructions stored, embodied, or encoded in a computer-readable medium, such as a computer-readable storage medium, containing instructions. Instructions embedded or encoded in a computer-readable medium may cause a programmable processor, or other processor, to perform the method, e.g., when the instructions are executed. Computer-readable storage media may include random access memory ("RAM"), read only memory ("ROM"), programmable read only memory (PROM), erasable programmable read only memory ("EPROM"), electronically erasable programmable read only memory ("EEPROM"), non-volatile random access memory ("NVRAM"), flash memory, a hard disk, a CD-ROM, a floppy disk, a cassette, a solid state drive, magnetic media, optical media, or other computer-readable media. Computer-readable media may be encoded with instructions corresponding to various aspects of network device <NUM>, e.g., protocols, processes, and modules. Control unit <NUM>, in some examples, retrieves and executes the instructions from memory for these aspects. Additionally or alternatively a computer-readable medium can include transient media such as carrier signals and transmission media.

Routing component <NUM> includes kernel <NUM>, which provides a run-time operating environment for user-level processes. Kernel <NUM> may represent, for example, a UNIX operating system derivative such as Linux or Berkeley Software Distribution (BSD). Kernel <NUM> offers libraries and drivers by which user-level processes may interact with the underlying system. Hardware environment <NUM> of routing component <NUM> includes microprocessor <NUM> that executes program instructions loaded into a main memory (not shown in <FIG>) from a storage device (also not shown in <FIG>) in order to execute the software stack, including both kernel <NUM> and processes executing on the operating environment provided by kernel <NUM>. Microprocessor <NUM> may represent one or more general- or special-purpose processors such as a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or any other equivalent logic device. Accordingly, the terms "processor" or "controller," as used herein, may refer to any one or more of the foregoing structures or any other structure operable to perform techniques described herein.

Kernel <NUM> provides an operating environment that executes various protocols <NUM> at different layers of a network stack, including protocols for implementing Ethernet Virtual Private Networks. For example, routing component <NUM> includes network protocols that operate at a network layer of the network stack. In the example of <FIG>, network protocols include the Border Gateway Protocol (BGP) <NUM>, which is a routing protocol. In particular, network device <NUM> may use a BGP route advertisement message to announce reachability information for the EVPN, where the BGP route advertisement specifies one or more MAC addresses learned by network device <NUM> instead of L3 routing information. Network device <NUM> updates routing information <NUM> based on the BGP route advertisement message. Network protocols <NUM> also includes Neighbor Discovery Protocol <NUM>.

Network device <NUM> may use NDP <NUM> to send and receive neighbor discovery messages including router solicitation messages, router advertisement messages, neighbor solicitation messages, neighbor advertisement messages, and redirect messages. Network device <NUM> may use SEcure Neighbor Discovery (SEND) <NUM> to provide security extensions for NDP <NUM>. Network device <NUM> may use SEND <NUM> to provide cryptographic mechanisms for network device <NUM> to secure delivery and authentication of neighbor discovery messages. For example, network device <NUM> may include a nonce with neighbor discovery messages to prevent replay attacks.

Routing component <NUM> may also include other protocols, such as an MPLS label distribution protocol and/or other MPLS protocols not shown in <FIG>. Routing component <NUM> is responsible for the maintenance of routing information <NUM> to reflect the current topology of a network and other network entities to which network device <NUM> is connected. In particular, routing protocols periodically update routing information <NUM> to accurately reflect the topology of the network and other entities based on routing protocol messages received by network device <NUM>.

Kernel <NUM> includes an interfaces table <NUM> ("interfaces <NUM>") that represents a data structure that includes a corresponding entry for each logical interface configured for network device <NUM>. Logical interfaces may correspond to local interfaces of network device <NUM> for Ethernet segments. Entries for respective logical interfaces may specify respective current information describing the logical interfaces.

Routing information <NUM> may include information defining a topology of a network, including one or more routing tables and/or link-state databases. Typically, the routing information defines routes (i.e., series of next hops) through a network to destinations / prefixes within the network learned via a distance-vector routing protocol (e.g., BGP) or defines the network topology with interconnected links learned using a link state routing protocol (e.g., IS-IS or OSPF).

Routing component <NUM> also includes an EVPN module <NUM> that performs L2 learning using BGP <NUM>. EVPN module <NUM> may maintain tables for each EVI established by network device <NUM>, or in alternative examples, may maintain one or more tables that are independent of each respective EVI. Network device <NUM> may use EVPN module <NUM> to advertise, e.g., EVPN routes, including Ethernet AD routes (Type <NUM>) to advertise reachability of network device <NUM> for an Ethernet segment, Ethernet segment routes (Type <NUM>) to discover other network devices of the Ethernet segment and for purposes of designated forwarder (DF) election (and backup DF election) for the Ethernet segment, and others. EVPN module <NUM> may store information from the EVPN routes, such as the identification of network devices of an Ethernet segment.

Forwarding component <NUM> represents hardware and logic functions that provide high-speed forwarding of network traffic. Forwarding component <NUM> typically includes a set of one or more forwarding chips programmed with forwarding information <NUM> that maps network destinations with specific next hops and the corresponding outbound interface ports. In general, when network device <NUM> receives a packet via one of inbound links <NUM>, forwarding component <NUM> identifies an associated next hop for the data packet by traversing the programmed forwarding information <NUM> based on information within the packet. Forwarding component <NUM> forwards the packet on one of outbound links <NUM> mapped to the corresponding next hop. At this time, forwarding component <NUM> may push and/or pop labels from the packet to forward the packet along a correct label switched path. Forwarding information <NUM> may be maintained in the form of one or more tables, link lists, radix trees, databases, flat files, or any other data structures.

Routing component <NUM> also includes an EVPN module <NUM> that performs L2 learning using BGP <NUM>. EVPN module <NUM> may maintain tables for each EVI established by PE device <NUM>, or in alternative examples may maintain one or more tables that are independent of each respective EVI. PE device <NUM> may use EVPN module <NUM> to advertise, e.g., EVPN routes including Ethernet AD routes (Type <NUM>) to advertise reachability of PE device <NUM> for an Ethernet segment, Ethernet segment routes (Type <NUM>) to discover other PE devices of the Ethernet segment and for purposes of DF election (and backup DF election) for the Ethernet segment, and other EVPN routes. EVPN module <NUM> may store information from the routes, such as the identification of PE devices of an Ethernet segment.

Routing component <NUM> includes a configuration interface <NUM> that receives and may report configuration data for network device <NUM>. Configuration interface <NUM> may represent a command line interface; a graphical user interface; Simple Network Management Protocol ("SNMP"), Netconf, or another configuration protocol; or some combination of the above in some examples. Configuration interface <NUM> receives configuration data configuring the network device <NUM>, and other constructs that at least partially define the operations for network device <NUM>, including the techniques described herein.

In accordance with the techniques described herein, routing component <NUM> may include a neighbor discovery security module <NUM> ("ND security module <NUM>") that performs the techniques described in this disclosure. For example, ND security module <NUM> provides security extensions, e.g., SEND <NUM>, to a neighbor discovery protocol, e.g., NDP <NUM>, in EVPN. In the examples described below, a user or administrator may use configuration interface <NUM> to configure ND security module <NUM> to configure network device <NUM> to operate in provide security extensions, e.g., SEND, to neighbor discovery in EVPN, as described in this disclosure. For example, configuration interface <NUM> may include an option to configure network device <NUM> to relax the nonce validation requirement, to specify a physical IP address of network device <NUM> as a source address of a neighbor discovery message, and/or to operate as an EVPN-proxy for neighbor discovery, in accordance with the techniques described in this disclosure. In some examples, the configuration of network device <NUM> to provide security extensions to neighbor discovery in EVPN may be "switched off' via configuration changes through configuration interface <NUM>.

In some examples in which network device <NUM> is multi-homed in a collapsed IP fabric (e.g., leaf device 10A in the example of <FIG>), ND security module <NUM> is configured to determine whether a neighbor discovery response message, e.g., neighbor discovery advertisement message, includes a nonce originated by network device <NUM>. For example, ND security module <NUM> may determine whether a nonce included in a neighbor discovery advertisement message matches a nonce stored in network device <NUM> (in memory not shown in <FIG>). In response to determining that network device <NUM> did not originate the nonce, ND security module <NUM> may determine whether the neighbor discovery advertisement message was received on an interface of an Ethernet segment (e.g., Ethernet segment <NUM> of <FIG>). For example, ND security module <NUM> may use EVPN module <NUM> to identify the leaf devices of the Ethernet segment (e.g., based on the advertised Ethernet segment routes (Type <NUM>)). In response to determining that the neighbor discovery advertisement message was received on an interface of Ethernet segment <NUM>, ND security module <NUM> may drop the nonce from the neighbor discovery advertisement message, learn the link layer addresses in neighbor discovery advertisement message, and store the learned addresses in routing information <NUM>.

In some examples in which network device <NUM> is multi-homed in a non-collapsed IP fabric (e.g., leaf device 10A in the example of <FIG>), ND security module <NUM> is configured to specify a source address of a neighbor discovery request message (e.g., neighbor discovery solicitation message) as a physical IP address. For example, network device <NUM> operates as a sender device and ND security module <NUM> may cause network device <NUM> to send a neighbor solicitation message including a nonce and a source address of the neighbor solicitation message specifying a physical IP address of network device <NUM> rather than a virtual IP address of an IRB interface.

In some examples in which network device <NUM> implements EVPN-proxy (e.g., PE device 510B of <FIG>), ND security module <NUM> is configured to intercept a first neighbor discovery response message (e.g., neighbor advertisement message <NUM> of <FIG>) from a local host device connected to network device <NUM> (e.g., endpoint 504B of <FIG>), that was generated in response to the first neighbor request message (e.g., neighbor solicitation message <NUM> of <FIG>) from a remote host device (e.g., endpoint 504A of <FIG>). ND security module <NUM> determines whether the nonce included in neighbor advertisement message <NUM> intercepted from local host device endpoint 504B is not originated by network device <NUM>. More specifically, ND security module <NUM> determines whether the nonce included in neighbor advertisement message <NUM> matches a nonce stored in network device <NUM>. In this example, since network device <NUM> did not originate the nonce, ND security module <NUM> determines that the nonce included in neighbor advertisement message <NUM> does not match a nonce stored in network device <NUM>.

ND security module <NUM> drops neighbor advertisement message <NUM> and sends a new neighbor discovery request message (e.g., neighbor solicitation message <NUM> of <FIG>) including the nonce. The local host device, endpoint 504B, receives neighbor solicitation message <NUM> including the nonce, and in response, sends a second neighbor discovery response message (e.g., neighbor advertisement message <NUM> of <FIG>) including the nonce. Network device <NUM> receives neighbor advertisement message <NUM> including the nonce. In response to determining that the nonce in neighbor advertisement message <NUM> matches the nonce in neighbor solicitation message <NUM>, ND security module <NUM> causes network device <NUM> to store one or more link layer addresses learned from neighbor advertisement message <NUM>. For example, ND security module <NUM> may store the locally learned addresses in routing information <NUM> (e.g., in a proxy table not shown in <FIG>). ND security module <NUM> may also send MAC/IP Advertisement routes (Type <NUM>) to remote PE devices (e.g., PE device 510A of <FIG>) to advertise the locally learned link layer addresses. ND security module <NUM> may also receive MAC/IP Advertisement routes from remote PE devices to learn link layer addresses from remote host devices.

In this way, when network device <NUM> receives a third Neighbor Discovery request message (e.g., neighbor solicitation message <NUM> of <FIG>) from a local host device (e.g., endpoint 504C of <FIG>), network device <NUM> may act as a proxy by using the learned link layer addresses stored in routing information <NUM> to reply locally to endpoint 504C to reduce the flooding of neighbor discovery messages over an EVPN core.

In addition to or as an alternative to the above, the following examples are described. The features described in any of the following examples may be utilized with any of the other examples described herein.

<FIG> is a flowchart illustrating an example operation of a network system configured to provide security extensions, e.g., SEND, to neighbor discovery in EVPN, in accordance with one or more aspects of the techniques described in this disclosure. <FIG> is described with respect to the examples described in <FIG>.

In the example of <FIG>, a network device implementing EVPN receives a neighbor discovery response message including a nonce originated by a second network device and not originated by the first network device (<NUM>). As one example, each of spine devices <NUM> is communicatively coupled to each of leaf devices 10A-10N, and servers <NUM> are directly connected to leaf devices <NUM> that operate as both L2 and L3 gateways, and is thus arranged as a collapsed IP fabric (as shown in the example of <FIG>). In these examples, the sender device, leaf device 10A, may send a neighbor discovery request message, e.g., neighbor solicitation message <NUM>, including a nonce to server 11A. Server 11A responds to the neighbor solicitation message <NUM> with a neighbor discovery response message, e.g., neighbor advertisement message <NUM>, including the nonce from neighbor solicitation message <NUM>. In some instances, leaf device 10B may receive the neighbor advertisement message <NUM> including a nonce that leaf device 10B did not originate.

As another example, leaf devices 10A and 10B are in a non-collapsed IP fabric (as shown in the example of <FIG>). In these examples, the sender device, leaf device 10A, may send a neighbor discovery request message, e.g., neighbor solicitation message <NUM>, including a nonce to intermediate switch 18A, which switches the neighbor solicitation message <NUM> to server 11A. Server 11A responds to the neighbor solicitation message <NUM> with a neighbor discovery response message, e.g., neighbor advertisement message <NUM>, including the nonce from neighbor solicitation message <NUM>. Server 11A may send the neighbor advertisement message <NUM> to intermediate switch 18A, which load balances the neighbor advertisement message <NUM> on any of the links of Ethernet segment <NUM>. In some instances, leaf device 10B receives the neighbor advertisement message <NUM> including a nonce that leaf device 10B did not originate.

In yet another example, in a network implementing EVPN-Proxy (as shown in the example of <FIG>), PE device 510B may intercept neighbor advertisement message <NUM> from endpoint 504B to learn the local link layer address of endpoint 504B. In this example, PE device 510B intercepts neighbor advertisement message <NUM> that includes a nonce that is not originated by PE device 510B.

The first network device may process the neighbor discovery response message including the nonce originated by the second network device and not originated by the first network device (<NUM>). In a collapsed IP fabric example, the first network device (e.g., leaf device 10B) determines whether the first network device originated the nonce. In response to determining that the first network device did not originate the nonce, the first network device determines whether the neighbor discovery response message was received on an Ethernet segment identifier (ESI) interface of the Ethernet segment. In response to determining that the neighbor discovery response message was received on the ESI interface of the Ethernet segment, the first network device drops the nonce from the neighbor discovery response message to learn a link layer address from the neighbor discovery response message.

In a non-collapsed IP fabric example, the first network device (e.g., leaf device 10B) determines that a destination address of the neighbor discovery response message is a physical IP address of the second network device. In response to determining that the destination address of the neighbor discovery response message is the physical IP address of the second network device, the first network device sends the neighbor discovery response message to the second network device via an overlay network.

In an EVPN-Proxy example, the first network device intercepts, from a local host device, the first neighbor discovery response message including the nonce, wherein the first neighbor discovery response message is generated by the local host device in response to a first neighbor discovery request message and destined for a remote host device. The first network device determines whether the first network device originated the nonce. In response to determining that the first network device did not originate the nonce, the first network device drops the first neighbor discovery response message, sends a second neighbor discovery request message to the local host device, wherein the second neighbor discovery request message includes the nonce originated by the first network device, and stores the nonce. The first network device receives, from the local host device, a second neighbor discovery response message including the nonce; in response to determining that the nonce is stored in the first network device, and stores one or more link layer addresses learned from the second neighbor discovery response message.

Thus, from one perspective, techniques have now been described for providing security extensions to neighbor discovery in Ethernet Virtual Private Network (EVPN). For example, a network device that implements Ethernet Virtual Private Network (EVPN) receives a neighbor discovery response message including a nonce originated by a second network device and not originated by the first network device. The network device processes the neighbor discovery response message including the nonce originated by the second network device and not originated by the first network device.

The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a network device, an integrated circuit (IC) or a set of ICs (i.e., a chip set). Any components, modules or units have been described provided to emphasize functional aspects and does not necessarily require realization by different hardware units. The techniques described herein may also be implemented in hardware or any combination of hardware and software and/or firmware. Any features described as modules, units or components may be implemented together in an integrated logic device or separately as discrete but interoperable logic devices. In some cases, various features may be implemented as an integrated circuit device, such as an integrated circuit chip or chipset.

If implemented in software, the techniques may be realized at least in part by a computer-readable storage medium comprising instructions that, when executed in a processor, performs one or more of the methods described above. The computer-readable storage medium may be a physical structure, and may form part of a computer program product, which may include packaging materials. In this sense, the computer readable medium may be non-transitory. The computer-readable storage medium may comprise random access memory (RAM) such as synchronous dynamic random access memory (SDRAM), read-only memory (ROM), non-volatile random access memory (NVRAM), electrically erasable programmable read-only memory (EEPROM), FLASH memory, magnetic or optical data storage media, and the like.

Claim 1:
A method comprising:
receiving (<NUM>), by a first network device that participates in an Ethernet Virtual Private Network, EVPN, and is coupled to a multi-homed host device by an Ethernet segment, a neighbor discovery response message including a nonce;
and
processing (<NUM>), by the first network device, the neighbor discovery response message including the nonce, wherein processing the neighbor discovery response message including the nonce further comprises:
determining, by the first network device, whether the first network device originated the nonce, wherein determining whether the first network device originated the nonce comprises determining, by the first network device, whether the nonce of the neighbor discovery response message matches a nonce stored in the first network device;
in response to determining that the first network device did not originate the nonce, determining, by the first network device, whether the neighbor discovery response message was received on an Ethernet segment identifier, ESI, interface of the Ethernet segment; and
in response to determining that the neighbor discovery response message was received on the ESI interface of the Ethernet segment, dropping the nonce from the neighbor discovery response message and learning a link layer address of the multi-homed host device from the neighbor discovery response message.