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Cisco Bug: CSCvs05863 - 7.1.1: BGP PIC turning to BGP Multipath after PIC core trigger without FRR

Last Modified

Jun 17, 2020

Products (1)

  • Cisco ASR 9000 Series Aggregation Services Routers

Known Affected Releases

7.1.1.BASE

Description (partial)

Symptom:
'show cef <bgp prefix> detail' may display two slots in the hash table, eg,

RP/0/0/CPU0:ios#show cef 5.5.5.5/32 detail 
Wed Nov 13 10:54:48.612 EST
5.5.5.5/32, version 8, internal 0x1000001 0x0 (ptr 0x4dc77c3c) [1], 0x0 (0x4dd27eac), 0xa08 (0x4e0e3058)
 Updated Nov 13 10:54:27.598
 Prefix Len 32, traffic index 0, precedence n/a, priority 0
  gateway array (0x4dc7988c) reference count 3, flags 0x300078, source rib (7), 0 backups
                [2 type 5 flags 0x451 (0x4e057160) ext 0x0 (0x0)]
  LW-LDI[type=5, refc=3, ptr=0x4dd27eac, sh-ldi=0x4e057160]
  gateway array update type-time 1 Nov 13 10:54:27.598
 LDI Update time Nov 13 10:54:27.657
 LW-LDI-TS Nov 13 10:54:27.649
   via 2.2.2.2/32, 3 dependencies, recursive [flags 0x0]
    path-idx 0 NHID 0x0 [0x4d78d80c 0x0], Internal 0x4e14f2d0
    recursion-via-/32
    next hop 2.2.2.2/32 via 64000/0/21
     local label 64002 
     next hop 16.0.0.2/32 UNKNOWN intf 0x00000014 labels imposed {8005 88}
   via 4.4.4.4/32, 3 dependencies, recursive, backup [flags 0x100]
    path-idx 1 NHID 0x0 [0x4d78d65c 0x0]
    recursion-via-/32
    next hop 4.4.4.4/32 via 64006/0/21
     local label 64002 
     next hop 16.0.0.2/32 UNKNOWN intf 0x00000014 labels imposed {ExpNullv4 32561}

    Load distribution: 0 1 (refcount 2)

    Hash  OK  Interface                 Address
    0     Y   recursive                 64000/0        
    1     Y   recursive                 64006/0        
RP/0/0/CPU0:ios#

Conditions:
1 - BGP PIC with primary/backup, loopback peering
2 - IGP has no protection, single path. Different interfaces for primary and backup
3 - shut down the primary interface, the primary IGP path changes to use the backup interface
4 - then it may hit the issue, but not always. There are some unknown control-plane conditions at play
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