Symptom

Observed that if we configure an IPv6 address which is overlapping on two different L3 interfaces of the same box using different subnets, no warning message is seen. This is not the case for IPv4. N9K-2-382(config-if)# int loop29 N9K-2-382(config-if)# ipv6 add 2001:db0::1/72 <<< 2001:db0::1/72 configured on loop29 N9K-2-382(config-if)# no shut N9K-2-382(config-if)# int loop31 N9K-2-382(config-if)# ipv6 address 2001:db0::1/73 Address already configured on interface loopback29 <<< warning seen when the IP is duplicated N9K-2-382(config-if)# ipv6 add 2001:db0::1/68 Address already configured on interface loopback29 <<< warning seen when the IP is duplicated N9K-2-382(config-if)# ipv6 add 2001:db0::3/68 <<< accepted without warning

Conditions

Configure two IPv6 addresses which would be part of the same logical subnet based on bits used to two different L3 interfaces on the same box using different subnet mask length.

Workaround

Use a subnet calculator to ensure your addresses are not overlapping.

Further Problem Description