Nokia NRS II Composite (IS-IS): IS-IS on Nokia SR OS: Configuration, Verification and Troubleshooting

What the exam tests

This domain tests practical SR OS configuration, show commands, and a structured approach to adjacency and route problems.

Core rules

• Base configuration is under configure router isis <instance>: area-id, level-capability, interfaces, metrics and authentication.
• Interfaces are added under the IS-IS instance; interface-type point-to-point avoids DIS election and pseudonode LSPs on p2p links.
• passive advertises the interface prefix without forming adjacencies.
• Verification commands include show router isis adjacency, show router isis database, show router isis routes, show router isis interface and show router isis statistics.
• Adjacency stuck in Init usually means area mismatch, level mismatch, MTU mismatch or authentication failure.
• Missing routes usually mean LSP flooding failure, overload bit, metric style mismatch or SPF not run.

Worked example

A point-to-point adjacency between two SR OS routers stays Init. show router isis adjacency detail shows the neighbor system ID but no Up state. show router isis interface shows one side with a smaller MTU than the other, so large IIH or LSP packets are dropped. Raising the MTU on the smaller side, or correcting the interface MTU consistently, allows the adjacency to reach Up and LSPs to flood.

Traps

Mismatched level-capability; forgetting that a passive interface cannot form an adjacency; authentication mismatch; interface-type mismatch; assuming a route exists because the adjacency is Up.