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Cisco Bug: CSCvv95631 - Protected ADJ SID is missing 2nd label after doing couple of link flaps/restorations

Last Modified

Oct 09, 2020

Products (1)

  • Cisco ASR 9000 Series Aggregation Services Routers

Known Affected Releases

7.1.2.BASE

Description (partial)

Symptom:
A SR-MPLS protected adjacency SID has a TI-LFA backup path that uses the correct egress interface and nexthop address, but  is missing the last (prefix) label in the label stack. For example:

RP/0/0/CPU0:r100#sh isis adj det gi0/0/0/1
Tue Oct  6 07:42:07.505 PDT

IS-IS 1 Level-2 adjacencies:
System Id      Interface                SNPA           State Hold Changed  NSF IPv4 IPv6
                                                                               BFD  BFD 
r103           Gi0/0/0/1                *PtoP*         Up    24   00:00:50 Yes None None
  Area Address:           49.0001
  Neighbor IPv4 Address:  10.4.1.103*
  Adjacency SID:          24012 (protected)
   Backup label stack:    [16102, 16103]
   Backup stack size:     2
   Backup interface:      Gi0/0/0/2
   Backup nexthop:        10.1.1.101
   Backup node address:   20.1.0.103
  Non-FRR Adjacency SID:  24013
  Neighbor IPv6 Address:  fe80::39:5aff:fe2e:af57*
  Adjacency SID:          24015 (protected)
   Backup label stack:    [16202, 16203]
   Backup stack size:     2
   Backup interface:      Gi0/0/0/2
   Backup nexthop:        fe80::9c:2cff:fe1e:3682
   Backup node address:   2020:1000::103
  Non-FRR Adjacency SID:  24016
  Topology:               IPv4 Unicast
  Topology:               IPv6 Unicast
  BFD Status:             BFD Not Required, Neighbor Useable

However, the correct label stack is [16102, 16103] as in:

RP/0/0/CPU0:r100#sh isis adj det gi0/0/0/1
Tue Oct  6 07:35:09.979 PDT

IS-IS 1 Level-2 adjacencies:
System Id      Interface                SNPA           State Hold Changed  NSF IPv4 IPv6
                                                                               BFD  BFD 
r103           Gi0/0/0/1                *PtoP*         Up    21   00:02:55 Yes None None
  Area Address:           49.0001
  Neighbor IPv4 Address:  10.4.1.103*
  Adjacency SID:          24010 (protected)
   Backup label stack:    [16102, 16103]
   Backup stack size:     2
   Backup interface:      Gi0/0/0/2
   Backup nexthop:        10.1.1.101
   Backup node address:   20.1.0.103
  Non-FRR Adjacency SID:  24011
  Neighbor IPv6 Address:  fe80::39:5aff:fe2e:af57*
  Adjacency SID:          24014 (protected)
   Backup label stack:    [16202, 16203]
   Backup stack size:     2
   Backup interface:      Gi0/0/0/2
   Backup nexthop:        fe80::9c:2cff:fe1e:3682
   Backup node address:   2020:1000::103
  Non-FRR Adjacency SID:  24015
  Topology:               IPv4 Unicast
  Topology:               IPv6 Unicast
  BFD Status:             BFD Not Required, Neighbor Useable

Conditions:
The problem has been seen intermittently in a full-mesh topology.
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