Description

This article describes a scenario where some IPV6 routes that are not in the routing table appear in the ISIS database.

Symptoms

Topology:

QFX-A:ae22------isis------ae22:QFX-B

 

QFX-A has the IPv6 prefix '  fd00::1/128' in the ISIS database, but this prefix is not in the route table.

user1@host1> show isis database extensive iad6-dc01 | match fd00:1/128 

 V6 prefix: fd00::1/128 Metric: 0 Internal Up 
 IPv6 prefix: fd00::1/128 Metric 0 Up 

user1@host2> show route fd00::1 
 inet6.0: 482 destinations, 644 routes (267 active, 0 holddown, 377 hidden) 
 + = Active Route, - = Last Active, * = Both 
 ::/0 *[Static/5] 01:38:26, metric2 1000 
 > to 2001::172:yy:xx:zz via ae24.0 
 inet6.3: 17 destinations, 17 routes (17 active, 0 holddown, 0 hidden) 
 + = Active Route, - = Last Active, * = Both

Solution

This issue occurred because QFX-B did not configure IPv6 address on the interface, which caused QFX-A to not have IPv6 neighbor for the prefix's next hop.

Configure family inet6 address for QFX-B's interface ae22. Make sure both sides have the IPv6 neighbor for each other.

Command to configure the IPv6 address:

set interface ae22 unit 0 family inet6 address

Example:

 set interface ae22 unit 0 family inet6 address fd00::1/126

Modification History

2025-10-21 minor non-technical edit
2025-07-15: Minor non-technical update
2020-03-11: Article created