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