Recently we moved our data centre which is a Cisco UCS and Nexus Fabric design. After a very long day moving gear and reconnecting it all back up we couldn’t understand why one of our FEX’s kept flapping from the 5K fabric. The 5K fabric is multi homed to 2 FEX switches each in its on virtual port channel. We researched the issue and found that if your doing multi homing to more than one FEX switch you need to make sure the physical interface IDs on the 5K marry up.
5K-1 Port e1/29 (vpc101) -> 2K-1 Uplink Port 1
5K-2 Port e1/30 (vpc102) -> 2K-2 Uplink Port 1
5K-1 Port e1/29 (vpc101) -> 2K-1 Uplink Port 2
5K-2 Port e1/30 (vpc102) -> 2K-2 Uplink Port 2
As you can see above the 5K side is the same port number on each 5K connecting to a FEX. This fixed the flapping issue and ownership console error. Good times ensued and we could patch all our physical copper rack servers.