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Cisco Bug: CSCur47160 - CEF is showing Unresolved for BGP learned prefixes

Last Modified

Feb 11, 2018

Products (5)

  • Cisco IOS
  • Cisco ME 3600X-24TS-M Switch
  • Cisco ME 3600X-24CX-M Switch
  • Cisco ME 3600X-24FS-M Switch
  • Cisco ME 3800X-24FS-M Switch Router

Known Affected Releases

15.2(4)S

Description (partial)

Symptom:
A forwarding decision may be stuck in an unresolved state, preventing traffic from flowing to one or more destinations.

Conditions:
This behaviour may be seen after BGP updates, usually of a temporary nature, that route a prefix such as A.B.C.0 through an unresolved next-hop A.B.C.D. This can create a loop. It may also be seen when default routes use an unattached next-hop prefix that is unresolved, creating another kind of loop.

In some cases, even though there may be alternative paths that are not looped (eg: a looped repair path, but an unlooped primary path), the whole prefix is treated as looped, and thus unresolved.

The command "show ip cef <address> internal" can show whether a prefix is "looped" and "unresolved".
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Bug Details Include

  • Full Description (including symptoms, conditions and workarounds)
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