FRR9.1 FIB Global to VRF Update Issue

[beith12]

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Description

When configuring FRR9.1 in Provider Edge (PE) role with MPLS L3 VPNs running over ISIS SR underlay, a change in the Global FIB does not reflect in the VRF FIB.

Version

FRRouting 9.1 
Linux(6.1.0-17-amd64).

How to reproduce

1. Setup FRR9.1 in PE role, peering iBGP VPNv4 over loopbacks:

PE-2# sh isis ne
Area LAB:
  System Id           Interface   L  State        Holdtime SNPA
 debian-12           ens4        2  Up            28       2020.2020.2020
 debian-12           ens5        2  Up            27       2020.2020.2020

PE-2# sh ip fib vrf BLUE
VRF BLUE:
K>* 0.0.0.0/0 [255/8192] unreachable (ICMP unreachable), 00:01:15
B>  172.16.128.1/32 [200/0] via 1.1.1.1 (vrf default) (recursive), label 17, weight 1, 00:01:09
  *                           via 192.168.0.10, ens5 (vrf default), label 16001/17, weight 1, 00:01:09
  *                           via 192.168.0.14, ens4 (vrf default), label 16001/17, weight 1, 00:01:09

2. Disable an upstream interface and ensure Global FIB see this:

PE-2# sh isis ne
Area LAB:
  System Id           Interface   L  State        Holdtime SNPA
 debian-12           ens4        2  Up            27       2020.2020.2020

PE-2# sh ip fib 1.1.1.1
Routing entry for 1.1.1.1/32
  Known via "isis", distance 115, metric 21, best
  Last update 00:00:23 ago
  * 192.168.0.14, via ens4, label 16001, weight 1

3. Review VRF FIB for updates to NH of 1.1.1.1:

PE-2# sh ip fib vrf BLUE
VRF BLUE:
K>* 0.0.0.0/0 [255/8192] unreachable (ICMP unreachable), 00:04:24
B>  172.16.128.1/32 [200/0] via 1.1.1.1 (vrf default) (recursive), label 17, weight 1, 00:04:18
  *                           via 192.168.0.10, ens5 (vrf default), label 16001/17, weight 1, 00:04:18
  *                           via 192.168.0.14, ens4 (vrf default), label 16001/17, weight 1, 00:04:18

4. Disable other upstream peer and review VRF FIB:

PE-2# sh ip fib 1.1.1.1
% Network not in FIB

PE-2# sh ip fib vrf BLUE
VRF BLUE:
K>* 0.0.0.0/0 [255/8192] unreachable (ICMP unreachable), 00:07:00
B>  172.16.128.1/32 [200/0] via 1.1.1.1 (vrf default) (recursive), label 17, weight 1, 00:06:54
  *                           via 192.168.0.10, ens5 (vrf default), label 16001/17, weight 1, 00:06:54
  *                           via 192.168.0.14, ens4 (vrf default), label 16001/17, weight 1, 00:06:54

Expected behavior

Any changes in the Global FIB should feed into the VRF FIB for proper routing. Testing in FRR8.5.2 does not seem to produce the same issues.

Actual behavior

VRF FIB is not updated when Global FIB receives a topology change.

Additional context

No response

Checklist

• [X] I have searched the open issues for this bug.
• [X] I have not included sensitive information in this report.

[ton31337]

Could you provide the minimal configuration to reproduce the issue to reduce the time for us to verify?

[beith12]

@ton31337 Let me rebuild these and report back - the behavior seemed inconsistent.

[beith12]

Further results inconsistent - closing for now