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[MX] Changing the routing-instance RD on the fly may cause MPLS VPN reachability issues



Article ID: KB33606 KB Last Updated: 13 Jan 2022Version: 2.0

If the value of the route-distinguisher (RD) in a routing instance is changed on the fly, customers may encounter some reachability issues.

This article explains why this happens and how such a problem can be avoided.


  1. Ping from CE1 to CE2 does not work.


    CE1 ----- PE1 ---- MPLS Core --- PE2 --- CE2

    In the above example, if the value of the RD in PE1's routing instance is changed without deactivating the routing instance, connectivity may be lost between CE1 and CE2.

  2. You may see a value of -1 for kernel-id of the non-working routing instance.

show krt table | match
.inet.0: GF: 1 krt-index: 84 ID: 0 kernel-id: 27
.iso.0: GF: 2 krt-index: 15 ID: 0 kernel-id: 27
.iso.0: GF: 2 krt-index: 84 ID: 0 kernel-id: -1   <<<<< 
.inet6.0: GF: 6 krt-index: 15 ID: 0 kernel-id: 27
.inet6.0: GF: 6 krt-index: 84 ID: 0 kernel-id: -1 <<<<<
  1. You may see the krt table for this routing instance present on the router even after deleting the routing-instance configuration.‚Äč

  2. The issue cannot be resolved by deleting and re-adding the routing instance.



If a configuration change is made by using a method that is not recommended, the krt queue may get stuck and the krt table for the instance name may go into problematic state.

Further, even after deleting the instance, the krt table for this instance name may still remain, while displaying the wrong value (kernel-id:-1).



This issue can be resolved by either renaming the non-working routing instance or rebooting the router.

To avoid this kind of issue, follow the recommended steps to change an RD during a maintenance window:

  1. Deactivate the routing instance.
  2. Change the RD.

  3. Activate the routing instance.

Note: This is not required if you are configuring the RD for the first time.

A syslog message is introduced via PR1342942 which prints the following when such configuration changes are done.

RPD_RT_CATASTROPHIC_RD_CHANGE: catastrophic rd change in routing-instance <name>

For more information on changing an RD, see route-distinguisher.

Modification History:
2021-12-24: Added PR1342942 which will print the message, 'RPD_RT_CATASTROPHIC_RD_CHANGE: catastrophic rd change in routing-instance <name>'
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