Description

ISIS adjacency failed to establish after customer migrated physical link to logical AE bundle. ISIS adjacency was up earlier when it was running on physical interfaces  

Old Topology: MX1 [xe-1/0/0] ---- [xe-1/0/0] MX2   
New Topology: MX1 [AE0:xe-1/0/0] ---- [AE0:xe-1/0/0] MX2   

This article gives a possible reason and suggests what should be done to resolve the problem.

Symptoms

Successful ISIS adjacency is not listed under "show isis adjacency" command output. Further, newly created AE bundle is not listed under "show isis interface"

Solution

The issue was due to a missing configuration line. Issue resolved after adding "set interface ae0.0 family iso" 

Below are the list of checks that can be performed during the ISIS adjacency troubleshooting 

  • Physical Layer or Data link layer connectivity
  • Mismatched area (for L1 routers)
  • Authentication Failures 
  • Incorrect Interface type (Point to Point  or Multi Access)   
  • Failure to support minimum MTU of 1492
  • No NET Addressing Configured 
  • Failure to include lo0 as an IS-IS Interface

Modification History

2024-05-03 : Article Created