Source: Configuring Nexus vPC – Part 1
Inconsistent echo-reply from devices connected via VPC to Nexus 9300 while pinging from the Nexus exec prompt.
With some of the testing I receive normal response when pinging from one Nexus, but no response when pinging from the other. In another test I receive a normal response to one Nexus, and duplicate replys to the other
HNINXP12# ping 172.22.36.1 source 172.22.82.3 vrf corp
PING 172.22.36.1 (172.22.36.1) from 172.22.82.3: 56 data bytes
64 bytes from 172.22.36.1: icmp_seq=0 ttl=251 time=3.249 ms
64 bytes from 172.22.36.1: icmp_seq=0 ttl=251 time=3.643 ms (DUP!)
64 bytes from 172.22.36.1: icmp_seq=1 ttl=251 time=3.213 ms
64 bytes from 172.22.36.1: icmp_seq=1 ttl=251 time=3.563 ms (DUP!)
“When you enable this feature (peer-gateway), Cisco NX-OS automatically disables IP redirects on all interface VLANs mapped over a vPC VLAN to avoid generation of IP redirect messages for packets switched through the peer gateway router.”
You will need to manually add “no ip redirects” on each VPC vlan interface to prevent duplicate pings.