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Cisco Bug: CSCuw28202 - HW CEF entry is not updated after changing igp topology

Last Modified

Jul 21, 2018

Products (1)

  • Cisco Carrier Routing System

Known Affected Releases

5.1.2.BASE

Description (partial)

Symptom:
Symptom 1.
When IGP topology is changed(e.g. ospf cost change), HW CEF for the bgp prefix, which needs two or more recursive lookup like the following, is not updated and old egress path info(tunnel-te A) remains.

- affected BGP prefix : X.X.X.X/28 (nexthop Y.Y.Y.Y)
- other BGP prefix    : Y.Y.Y.0/24 (nexthop Z.Z.Z.Z)
- IGP prefix          : Z.Z.Z.0/24 (egress IF before IGP change: tunnel-te A, egress IF after IGP change: tunnel-te B, )

Symptom 2.
after sysmptom 1, if down event of tunnel-te A which is old info in the HW CEF entry happens, the adjacency info in the HW CEF entry becomes invalid state and packet drop continues with increase of PAT drop counter. (e.g. TLU entry has invalid TLU_ID,  MPLS FIB NH Drop)

Conditions:
When router matches all of the following condition and trigger, the issue happens.

 Condition: 
  A. there is bgp routes which need two or more recursive lookup
  B. the nexthop of the routes of condition A is tunnel-te
  C. there is IGP route that depth_changed flag in CEF entry is 0. (egress IF of this IGP route is tunnel-te B in the above symptom 1)

 Trigger of Symptom 1 : change igp topology (e.g. ospf cost change)
 Trigger of Symptom 2 : down/up of tunnel-te A which is old egress IF for the prefix of symptom 1.
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