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Cisco Bug: CSCul45717 - Maxaged LSA with failure reason "Ack count not zero" is seen

Last Modified

Nov 27, 2020

Products (23)

  • Cisco ASR 9000 Series Aggregation Services Routers
  • Cisco CRS-1 Line Card Chassis (Dual)
  • Cisco CRS-1 Line Card Chassis (Multi)
  • Cisco CRS-3 Multishelf System
  • Cisco CRS-1 16-Slot Line Card Chassis
  • Cisco ASR 9922 Router
  • Cisco CRS-1 4-Slot Single-Shelf System
  • Cisco IOS XR Software
  • Cisco ASR 9010 Router
  • Cisco XR 12410 Router
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Known Affected Releases

4.3.1.BASE

Description (partial)

Symptom:
An maxaged LSA (with age much bigger than 3600) might be present in the ospf database, and on the maxage list.
The reason for not deleting the LSA (which can be displayed with "show ospf database <LSA_type> <LSA_ID> internal" is "Ack count not zero"

In MPLS/TE deployments, the problem may cause that all TE tunnels to a given TE router could go down for up to 1 hour.

In other deployments, when these LSAs are present in multiple routers, they may result in flooding war between neighbours with different versions of the LSA. This in turn causes re-transmissions and CPU spike which may also cause adjacency flaps or other issues in the system.

Conditions:
The problem may happen under special timing conditions, when the interface goes down in ospf while the process was waiting for an ACK for that LSA from the interface.

The MPLS/TE network gets affected when this problem happens to the opaque LSA that carries the MPLS TE router ID, and the OSPF router ID is changed in the configuration, while the MPLS TE router ID remains the same.
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Bug Details Include

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