MPLS ArchitecturalConsiderations for OAM
MPLS Japan
Monique Morrow
mmorrow@cisco.com© 2002, Cisco Systems, Inc. All rights reserved.

1Motivation• Overview of MPLS OAM Issues• Structure tools to focus in strength areas© 2002, Cisco Systems, Inc. All rights reserved.

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Agenda• Challenges• MPLS Architecture• ITU defined OAM• LSP Ping
• Application Specific OAM• MIB Overview• Cisco Network Health Monitor• Summary© 2002, Cisco Systems, Inc. All rights reserved.

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Challenges• One tool does not fit all• Fault monitoring• Fault detection• Service Level Agreement Management• Quality of Service• Tools that are appropriate© 2002, Cisco Systems, Inc. All rights reserved.

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Challenges: An Example
Virtual Circuits

Label Switched Paths

Established via ATM
Signaling orManagement
Bi-directional

Establishment tiedclosely to control planes

Connection oriented

Can be “connectionless”

Single routeMay use ECMP

No penultimate popping

Penultimate hop popping

Fixed hierarchy VP/VC

Variable Label Stack© 2002, Cisco Systems, Inc. All rights reserved.

Usually Uni-directional

5Agenda• Challenges• MPLS Architecture• ITU defined OAM• LSP Ping
• Application Specific OAM• MIB Overview• Cisco Network Health Monitor• Summary© 2002, Cisco Systems, Inc. All rights reserved.

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Applications & Labels• Applications can directly
manipulate label bindings

TrafficEngineering

UnicastRouting
FrameRelay• Forwarding component
Simple label-swapping paradigm

DifferentiatedServices
VirtualPrivateNetworks

Efficient lookup and forwarding
Per-Label Forwarding, Queuing,and Multicast Mechanisms• Separation allows flexibility© 2002, Cisco Systems, Inc. All rights reserved.

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Label Stack
UnicastUnicastRoutingRouting• Arbitrary number of labels• Label Stack Operations
Push- add a label to the stack
Swap - replace the top label
Pop - remove the top label

Traffic
TrafficEngineering
Engineering

VPNVPN

Traffic
Traffic Engineering
Engineering
UnicastUnicast Routing
Routing
VirtualVirtual Private
Private NetworkNetwork• Allows multiple control
planes to act on a packet• Eases the integration of applications© 2002, Cisco Systems, Inc. All rights reserved.

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MPLS & IP Routing• IP offers a connectionless service• The primary function of LDP is to distributelabels to support IP routing• Labels distributed by LDP are under control ofthe IGP• IGP LSPs are not static entities• These LSPs may be rerouted at any node at anytime© 2002, Cisco Systems, Inc. All rights reserved.

9Equal Cost Multi-Path (ECMP)
R3
R1

R5R2R4• IP uses shortest path routing• Traffic can be split across multiple shortest paths• Most deployed label switching boxes use the bottom
most label in their ECMP algorithm
Adding an OAM label at the bottom may change thebehavior that is being measured© 2002, Cisco Systems, Inc. All rights reserved.

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Penultimate hop popping
AddressPrefix

Out OutLabel IFInOut Out
Label Label IF

128.89.10

313-0

171.6941471

10.225.1.1

61

6-1

LER forwards Packet
on IP Header

128.89.10
01
128.89.10.1
171.69.12.1 data

34 128.89.10.1
171.69.12.1 data1

One lookup is more efficientLabel Switch Router does athan two
Swapoperation
operationtotosend
sendpacket
packetPop
anotherLSR
to a
Label
RouterLabel
is noEdge
longeravailable
for LSP identification© 2002, Cisco Systems, Inc. All rights reserved.

128.89.10.1 data
7 171.69.12.1 data

10.225.1.1
To 171.69

11Agenda• Challenges• MPLS Architecture• ITU defined OAM• LSP Ping
• Application Specific OAM• MIB Overview• Cisco Network Health Monitor• Summary© 2002, Cisco Systems, Inc. All rights reserved.

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ITU MPLS OAM - Y.1711• Follows closely ATM OAM (I.610)• Three functions definedConnectivity Verification (CV)Forward Defect Indication (FDI)
Reverse Defect Indication (RDI)• OAM Alert Label
Reserved label value (14)Added at bottom of stack to identify OAM packet© 2002, Cisco Systems, Inc. All rights reserved.

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Y.1711 OAM Format

44 byte PayloadFunction Type (1 byte)
Trail Termination Source ID (20 bytes)
IPv6 Node ID (16 bytes)
LSP ID (4 bytes)

BIP-16 (2 bytes)
Other bytes specific to function type

© 2002, Cisco Systems, Inc. All rights reserved.

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Drawbacks of Y.1711• LSP Identification (TTSI)• Equal cost multi-path• Penultimate hop popping• Assumption of a fixed path
• Requirement for a reverse path
• Fixed interval between CV Packets© 2002, Cisco Systems, Inc. All rights reserved.

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LSP Identification (TTSI)• LSP ID is not a well defined term• Each application manages its LSPs independently – nocoordination of LSP identification across applications• Only point of commonality is a low level label database toensure uniqueness• 4 byte LSP ID field defined in Y.1711 is too small to use
application’s native identification• Use of this field would require a unique space to be
managed across applications and that LSP IDs be added to
all forms of MPLS signaling© 2002, Cisco Systems, Inc. All rights reserved.

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Requirement for a reverse path

• Some OAM functions assume that areverse LSP exists which can beassociated with the forward path
• This kind of association is the exception
rather than the rule for most MPLSapplications© 2002, Cisco Systems, Inc. All rights reserved.

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Agenda• Challenges• MPLS Architecture• ITU defined OAM• LSP Ping
• Application Specific OAM• MIB Overview• Cisco Network Health Monitor• Summary© 2002, Cisco Systems, Inc. All rights reserved.

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Rationales for IP based OAM• MPLS is IP-based• All MPLS control protocols are based on
the IP protocol suite
LDP / BGP / RSVP / PIM© 2002, Cisco Systems, Inc. All rights reserved.

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Rationales for IP based OAM (2)• The majority of MPLS applications carry IPtraffic
Even most Frame Relay & ATM traffic has IP asits payload• The primary goal of OAM is to ensure thecustomer is receiving the expected service© 2002, Cisco Systems, Inc. All rights reserved.

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LSP Ping• Similar to ICMP (IP) Ping
Sequence Number
Timestamps
Sender Identification• Full identification of FEC based on syntax andsemantics of the application• Variable length for MTU discovery• Support for tunnel tracing© 2002, Cisco Systems, Inc. All rights reserved.

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LSP Ping• Destination address in local host range (127.0.0/24)
Detects lack of MPLS connectivity even if there is IPconnectivity
Range allows coverage of Equal Cost Multi-Paths• Reply can be via IP or control plane or no reply• IP reply uses Router Alert to avoid LSPs
• Extensions to support recursive traceroute
GTTP – Generalized Tunnel Trace Protocol© 2002, Cisco Systems, Inc. All rights reserved.

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Agenda• Challenges• MPLS Architecture• ITU defined OAM• LSP Ping
• Application Specific OAM• MIB Overview• Cisco Network Health Monitor• Summary© 2002, Cisco Systems, Inc. All rights reserved.

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One Size does not Fit All• OAM is trying to measure applicationperformance• Most MPLS applications are IP related like MPLS
BGP VPN, RSVP-TE• However, some of the services targeted for
PWE3 have OAM requirements beyond those
provided by the current IP OAM suite© 2002, Cisco Systems, Inc. All rights reserved.

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PWE3 Network Reference Model
Emulated ServicePseudo Wire
PSN Tunnel
PW1

PE1

CE1PE2CE2PW2Native Service

Native ServicePWE3 does not run exclusively over MPLSPSN Tunnel may be MPLS, IPSEC, L2TP, GRE,…
Should PWE3 OAM be tied closely to MPLS?
© 2002, Cisco Systems, Inc. All rights reserved.

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Monitoring the tunnel
Emulated ServicePseudo Wire
PSN Tunnel
PW1

CE1

PE1

Native Service

PW2

PE2

CE2

Native Service• Tunnels may be MPLS, IPSEC, L2TP, GRE,…
• One tunnel can serve many pseudo-wires• IP based tools (including MPLS ping) are sufficient tomonitor the PSN tunnel• Verifies PE to PE connectivity• Frequent monitoring may be appropriate© 2002, Cisco Systems, Inc. All rights reserved.

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Pseudo-Wire Protocol Layers
PayloadEncapsulation

May be null

Virtual Circuit

Pseudo-Wire Demux

PSN Convergence
PSN

Usually null
MPLS, L2TP, IPSEC, etc.

MAC/Data-link
Physical• Encapsulation could be used to flag OAM• Alert label before or after Virtual Circuit could also beused© 2002, Cisco Systems, Inc. All rights reserved.

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Agenda• Challenges• MPLS Architecture• ITU defined OAM• LSP Ping
• Application Specific OAM• MIB Overview• Cisco Network Health Monitor• Summary© 2002, Cisco Systems, Inc. All rights reserved.

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MPLS MIB Overview at a Glance
MPLS

MPLS LSR MIB

CCAMPMPLS-TE MIB
MPLS-TC MIB

LMP MIB
MPLS-FTN-MIB

MPLS-LINKBUNDLING-MIB

GMPLSLSR/TE/Label
Table/TC MIBs?

MPLS-LDP-MIB

PPVPN
PWE3

Service-specific
MIBs…
PPVPN-TC MIB

PW-TC MIBPW MIBPPVPN-MPLSVPN MIB

PW-CEM MIB© 2002, Cisco Systems, Inc. All rights reserved.

PW-MPLS MIB

Depends on
Depends on
RFC2233
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MPLS based services - MIB
MPLS-VPN-MIB: draft-ietf-ppvpn-mpls-vpn-mib-04.txt
CISCO-PING-MIB

PW-MIB:draft-ietf-pwe3-pw-mib-00.txt (not implemented yet)
MPLS L2 VPN

MPLS L3 VPN

MPLS-TE-MIB:draft-ietf-mpls-te-mib-08.txt
CISCO-MPLS-TE-MIB
CISCO-MPLS-TOPO-MIBCISCO-MPLS-DS-TE-MIB

MPLS Traffic Engineering

PE

PEPE

PE

PE

MPLS Network
Physical Level (ATM, POS, DPT ...)
© 2002, Cisco Systems, Inc. All rights reserved.

PE

RFC2233: Interface MIB
LDP-MIB:draft-ietf-mpls-ldp-mib-08.txt
LSR-MIB:draft-ietf-mpls-lsr-mib-08.txt
MPLS-FTN-MIB:draft-ietf-mpls-ftn-mib-04.txt

CISCO-SRP-MIB (for DPT)
RFC1595: SONET MIBCISCO-SONET-MIB
RFC1213: MIB-2, RFC2233
CISCO-SYSLOG-MIB (for syslog)
CISCO-ENVMON-MIB (for env. monitor 30)

Agenda• Challenges• MPLS Architecture• ITU defined OAM• LSP Ping
• Application Specific OAM• MIB Overview• Cisco Network Health Monitor• Summary© 2002, Cisco Systems, Inc. All rights reserved.

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Cisco Health Monitor Application• Application residing in IOS that is responsible
for:Periodically verifying PW VC connection status using
MPLS LSP Ping/GTTP.
Continually monitoring the quality of a VC (e.g.:packet loss, jitter, etc…)
Automatically take user-programmed corrective
actions under curtain circumstances (e.g.: notify tunnel
manager to choose alternative tunnel that meets userrequirements).

Significantly automates health monitoring tasks!
© 2002, Cisco Systems, Inc. All rights reserved.

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Putting it All Together
MPLS
HealthMonitor Boston PE

Liberty St. PE

Bean St. CE
Revolution
Road CE

NYC PE

Orlando PE

P2P Ethernet PW
VC

MPLS
HealthMonitor

Chicago PE

Bears St. CE© 2002, Cisco Systems, Inc. All rights reserved.

Mickey Ave. CE
Fire Ave. CE
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SummarySolution must address MPLS needs• Independence of control planes• Uni-directional LSPs
• Penultimate hop popping• Equal Cost Multi-Path• Flexible binding up & down label stack© 2002, Cisco Systems, Inc. All rights reserved.

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Summary (2)• Most current applications offer an IP
related service• IP is the basis of MPLS control planes• IP based tools make sense© 2002, Cisco Systems, Inc. All rights reserved.

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Summary (3)• Applications vary widely in their OAM
requirements• Adaptable & tunable to application needs• One size does not fit all• MIBs enhance tool box• Cisco Network Health Monitor• Progress continues!

© 2002, Cisco Systems, Inc. All rights reserved.

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Thank You© 2002, Cisco Systems, Inc. All rights reserved.

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