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Cisco Bug: CSCur30073 - switch table driving wrong multipath

Last Modified

Sep 17, 2019

Products (1)

  • Cisco Nexus 7000 Series Switches

Known Affected Releases

6.2(10)S100 7.1(0)D1(0.266)

Description (partial)

On a VPC+ setup where Fabricpath multi-topology feature is being used and "no port-channel limit" is not being used, unicast traffic arriving at certain ports in the default topology, directed towards the VPC hosts might fail under certain race conditions.

The failure might be encountered if  in the system described above, if the first few VPCs are de-configured  followed  by moving ports of the VDC  to another VDC and then moving them back in. Based on certain race conditions, this sequence might sometimes cause incorrect forwarding of unicast traffic arriving at those ports (that were moved) if the destination is behind the VPCs on the VLANS belonging to the default topologies.

All of the below conditions are required at a minimum before there is a possibility to hit this issue. 
1. VPC+ with multiple Fabricpath topologies in use.
2. No port-channel limit configuration is not being used under VPC domain. If this configuration is being used the issue will not be encountered.
3. The first few  VPC legs that were brought up are de-configured.
4. Certain ports of the VPC+ VDC are moved out to another VDC and moved back in.
5. Unicast Traffic is arriving in the switch at any of those ports is directed towards the hosts behind the VPCs on the default Fabricpath topology may experience failure. Traffic on non-default topologies should not be affected.

This issue can be encountered if the ports that are moved between VDCS are F2, F2E or F3.
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