Unicast Data Plane Forwarding and Reachability
http://aci-troubleshooting-book.readthedocs.io/en/latest/unicast.html
In the situation where the mac address has been changed for an ip address. The device it is trying to reach also need to update its ARP table with new mac address. The device reported in the error may have been removed from the network is is moving for some reason and there is a discrepancy in the epmc tables when trying to be contacted.
If you see this issue of a device getting disconnected from network while it is still up and you know it is still sending traffic. Please gather a "techsupport local" from both vPC peers where the device is connected.
vsh_lc –c “show system internal epmc endpoint ip x.x.x.x” command can be used to see if the endpoint exist on the leaf nodes or not.
Also you can take a look at the operational tab of the EPG and look for the ip address and mac address of the device having issues.
If the error persists and the device is in the network and having issues, Please gather the "techsupport local" files for the affected switches and open a Cisco TAC case for assistance.
Thanks again for using the Cisco Support Community for ACI!
T.
