This article is useful for log collection and troubleshooting different scenarios of segment routing when ISIS is underlying IGP.
Below command outputs should be collected for all the issues you encounter while troubleshooting segment routing in ISIS environment.
show mpls interface show isis adjcacency show isis adjacency extensive show isis database extensive show route table inet.3 show isis overview
Step 1: Ensure that end-to-end MPLS LSP is established between PE1 and PE2 devices.
We need to verify below points:
lab@R2> show isis database extensive | no-more <snip> R6.00-00 Sequence: 0x4d, Checksum: 0xb376, Lifetime: 10703 secs IPV4 Index: 406, IPV6 Index: 606 Node Segment Blocks Advertised: Start Index : 0, Size : 9000, Label-Range: [ 1000, 9999 ] IS neighbor: R3.00 Metric: 1000 Two-way fragment: R3.00-00, Two-way first fragment: R3.00-00 P2P IPv4 Adj-SID: 18, Weight: 0, Flags: -BVL-- P2P IPv6 Adj-SID: 24, Weight: 0, Flags: FBVL-- P2P IPv4 Adj-SID: 600001, Weight: 3, Flags: -BVLSP IS neighbor: R4.00 Metric: 1000 Two-way fragment: R4.00-00, Two-way first fragment: R4.00-00 P2P IPv4 Adj-SID: 22, Weight: 0, Flags: -BVL-- P2P IPv6 Adj-SID: 25, Weight: 0, Flags: FBVL-- P2P IPv4 Adj-SID: 21, Weight: 0, Flags: -BVL-- P2P IPv6 Adj-SID: 23, Weight: 0, Flags: FBVL-- P2P IPv4 Adj-SID: 600001, Weight: 1, Flags: -BVLSP IS neighbor: R7.00 Metric: 1000 Two-way fragment: R7.00-00, Two-way first fragment: R7.00-00 P2P IPv4 Adj-SID: 19, Weight: 0, Flags: -BVL-- P2P IPv6 Adj-SID: 26, Weight: 0, Flags: FBVL-- IS neighbor: R8.00 Metric: 1000 Two-way fragment: R8.00-00, Two-way first fragment: R8.00-00 P2P IPv4 Adj-SID: 20, Weight: 0, Flags: -BVL-- P2P IPv6 Adj-SID: 27, Weight: 0, Flags: FBVL--
4. There should be ISIS labelled route in inet3.0 routing table.
192.168.1.1/32 *[L-ISIS/8] 00:00:08, metric 10 > to 10.10.10.2 via ge-0/0/1.0, Push 0 [LDP/9] 00:00:08, metric 1 > to 10.10.10.2 via ge-0/0/1.0
Issue 2: SR is preferred over LDP or LDP is preferred over SR
By default LDP is preferred over SR. To prefer SR route over LDP, label preference should be configured on ISIS.
Please refer KB: https://juniper.lightning.force.com/lightning/s/article/Configure-SR-preference-over-LDP
Issue 3: Duplicate Node-SID issue
Each router must have a unique node index.
Configure ISIS traceoptions: https://www.juniper.net/documentation/us/en/software/junos/cli-reference/topics/ref/statement/traceoptions-edit-protocols-isis.htmlBelow message in ISIS trace log file indicates SID conflict:
Jul 13 17:54:27.005877 Prefix_SID:67 from L2 LSP LSP-1 is inactive due to SID-conflict
Verify the node-SID value using below command:
lab@R2> show isis overview | no-more Instance: master Router ID: 192.168.0.2 Hostname: R2 Sysid: 1921.6800.0002 Areaid: 49.0000 Adjacency holddown: enabled Maximum Areas: 3 LSP life time: 65535 Reference bandwidth: 1000000000000 Attached bit evaluation: enabled SPF delay: 50 msec, SPF holddown: 2000 msec, SPF rapid runs: 5 Overload bit at startup is set Overload high metrics: disabled Allow route leaking: disabled Overload timeout: 300 sec IPv4 is enabled, IPv6 is enabled, SPRING based MPLS is enabled Traffic engineering: enabled Restart: Disabled Helper mode: Enabled Layer2-map: Disabled Source Packet Routing (SPRING): Enabled SRGB Config Range: SRGB Start-Label : 1000, SRGB Index-Range : 9000 SRGB Block Allocation: Success SRGB Start Index : 1000, SRGB Size : 9000, Label-Range: [ 1000, 9999 ] Node Segments: Enabled Ipv4 Index : 402, Ipv6 Index : 602 Post Convergence Backup: Disabled Level 1 Internal route preference: 15 External route preference: 160 Prefix export count: 0 Wide metrics are enabled, Narrow metrics are enabled Source Packet Routing is enabled Level 2 Internal route preference: 18 External route preference: 165 Prefix export count: 0 Wide metrics are enabled Source Packet Routing is enabled