An interesting client problem in one of our multi-tenant data centers came to my attention the other day. A delay sensitive client noticed a slight increase in latency (20 ms) at very intermittent intervals from his servers in our data center to specific off-net destinations. The increase in latency was localized to the pair of Nexus 7000′s functioning as the core switch layer (CSW) and the layer3 edge for this particular data center. Beyond that all appeared normal on the N7K CSWs.
A TCP dump from a normal trunk interface attached to the N7Ks, showed unicast traffic on the N7K-2 device when the N7K-1 device was setup to receive internet traffic inbound and forward it into the data center client VLANs. The N7Ks are setup using the Cisco VPC (Virtual Port Channels).