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Cisco Bug: CSCua84696 - MW relay not working when Access PWs are in default split-horizon-group

Last Modified

May 08, 2018

Products (5)

  • Cisco Carrier Routing System
  • Cisco IOS XR Software
  • Cisco ASR 9010 Router
  • Cisco ASR 9006 Router
  • Cisco ASR 9001 Router

Known Affected Releases

4.3.0.BASE

Description (partial)

Symptom:Upon switchover from active link to standby link, customer found MAC address number under AC/PW become 0, and MAC withdraw counter under the bridge-domain increasing rapidly.

MAC address couldn't be learned properly on the newly-active link, and L2 traffic is flooding in the bridge-domain.
Conditions:Access Pseudo-wires (PW) are configured in the core for a specific reason, rather than the recommended VFI configuration. In this case, Access PW were chosen because the MAC limit configuration at port level works only on Access PW.

To induce the MAC withdraw storm, Access PW and MAC address need to be updated between PEs: with the MAC withdraw configured on port-down for a bridge, shutting the access interface will trigger the first MAC withdraw message.
A switchover from active to standby will also generate an initial MAC withdraw.
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