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How to check if SRLG is working correctly on an LSP using only primary path LSPs (no secondary LSPs) with node-link protection

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Article ID: KB29677 KB Last Updated: 18 Jun 2015Version: 1.0
Summary:

The Shared Risk Link Group (SRLG) is configured so that the Constrained Shortest Path First (CSPF) algorithm tries to keep the links used for the primary and bypass paths mutually exclusive.

Symptoms:

Using show commands, how can we verify that that the protected path and the bypass path are not sharing any links?

Solution:

First we check the RSVP session to find out what the bypass LSP is, as well as which interface the primary path is using.

dan@test> show rsvp session ingress extensive name TL1-TL2-1:BE
Ingress RSVP: 592 sessions

192.168.1.2
From: 192.168.1.1, LSPstate: Up, ActiveRoute: 0
LSPname: TL1-TL2-1:BE, LSPpath: Primary
LSPtype: Static Configured
Suggested label received: -, Suggested label sent: -
Recovery label received: -, Recovery label sent: 567536
Resv style: 1 SE, Label in: -, Label out: 567536
Time left: -, Since: Mon Oct 27 17:01:49 2014
Tspec: rate 2Mbps size 2Mbps peak Infbps m 20 M 1500
Port number: sender 27 receiver 11533 protocol 0
Link protection desired
Type: Link protected LSP, using Bypass->192.168.1.101 <<<<<<<<<<< This is the bypass LSP
7 Nov 18 17:06:41 Link protection up, using Bypass->192.168.1.101
6 Nov 18 17:06:38 Bypass in down state, Bypass->192.168.1.101
5 Nov 18 17:06:38 Link protection down, due to re-optimization
4 Nov 18 17:04:28 Link protection up, using Bypass->192.168.1.101
3 Nov 18 17:03:34 Bypass in down state, Bypass->192.168.1.101
2 Nov 18 17:03:33 Link protection down, RSVP session down
1 Nov 18 17:02:42 Link protection up, using Bypass->192.168.1.101
PATH rcvfrom: localclient
Adspec: sent MTU 1500
Path MTU: received 1500
PATH sentto: 192.168.1.101 (et-0/0/1.0) 2 pkts <<<<<< Main LSP is riding on et-0/0/1.0
RESV rcvfrom: 192.168.1.101 (et-0/0/1.0) 1 pkts
Explct route: 192.168.1.101 140.222.248.200
Record route: <self> 192.168.1.3 (node-id) 192.168.1.101 192.168.1.2 (node-id) 192.168.1.200


Next we check the bypass path to check what interface is being used since it must be different than the primary path:

dan@test> show rsvp session bypass name Bypass->192.168.1.101 extensive
Ingress RSVP: 3 sessions

192.168.1.3
From: 192.168.1.1, LSPstate: Up, ActiveRoute: 0
LSPname: Bypass->192.168.1.101
LSPtype: Static Configured
Suggested label received: -, Suggested label sent: -
Recovery label received: -, Recovery label sent: 552800
Resv style: 1 SE, Label in: -, Label out: 552800
Time left: -, Since: Mon Oct 27 17:06:38 2014
Tspec: rate 0bps size 0bps peak Infbps m 20 M 1500
Port number: sender 1 receiver 11584 protocol 0
Type: Bypass LSP
Number of data route tunnel through: 159
Number of RSVP session tunnel through: 0
PATH rcvfrom: localclient
Adspec: sent MTU 1500
Path MTU: received 1500
PATH sentto: 192.168.1.19 (et-1/0/4.0) 2 pkts <<<<<<< The bypass LSP is riding on et-1/0/4
RESV rcvfrom: 192.168.1.19 (et-1/0/4.0) 1 pkts
Explct route: 192.168.1.19 140.222.248.201
Record route: <self> 192.168.1.19 192.168.1.201
Total 1 displayed, Up 1, Down 0

From the above output we can check the “PATH sentto”. This is the address of the next-hop (downstream) router interface used to reach this neighbor as well as the interface used. As we can see, both the primary path and the bypass are using diffferent links which indicates that SRLG is working as expected.

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