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Cisco Bug: CSCvi12661 - BGP Crash or stale info on standby RSP with aggregate config and aggregate prefix learned from peer.

Last Modified

Aug 14, 2019

Products (1)

  • Cisco ASR 9000 Series Aggregation Services Routers

Known Affected Releases

5.3.3.BASE

Description (partial)

Symptom:
1.BGP Crash on standby RSP
or 
2. Stale routing information on standby RSP for aggregate addresses (V4/V6)

Way to detect is, to compare for # of available paths for aggregate-addresses in active vs standby RSP

sh bgp [vrf ID] ipv4 uni IPv4_PFX | i avail
 
and
 
sh bgp [vrf ID] ipv4 uni IPv4_PFX stand | i avail
  
 
OR
 
 
sh bgp [vrf ID] ipv6 uni IPv6_PFX | i avail
 
and
 
sh bgp [vrf ID] ipv6 uni IPv6_PFX stand | i avail
 
look for paths available (how many) and best path index. It needs to match b/w Active and Stby.
 
 
RP/0/RP0/CPU0:#sh bgp vrf <> ipv4 uni <> | i avail
Paths: (17 available, best #1)
RP/0/RP0/CPU0:#sh bgp vrf <> ipv4 uni <> stand | i avail
Paths: (17 available, best #1)
  
RP/0/RP0/CPU0:#sh bgp ipv4 uni <> | i avail
Paths: (3 available, best #3)
RP/0/RP0/CPU0:#sh bgp ipv4 uni <> stand | i avail
Paths: (8 available, best #1)

Conditions:
The issue is seen when we have an aggregate route is configured and following event occurs:

Initially prefix has 2 paths:
Path1: aggregate
Path2: learned from neighbor
Path2 gets withdrawn.
Path2 is re-advertised.
On standby we add another(redundant) aggregate path via NSR sync code path if standby processes this NSR sync event before network event. 
So this is based on timing condition.
standby bgp crashes if redundant path count wraps unsigned integer value.

Note: This issue will not happen if NSR is disabled for bgp process.
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