Symptom

Packets are dropped due to IPv6 unicast RPF failures when loose IPv6 unicast RPF is configured and we have an IPv6 route for the source of the IPv6 packet pointing at another interface. RP/0/RP0/CPU0:router#show cef ipv6 drops location 0/3/CPU0 Tue Sep 2 12:06:45.072 UTC CEF Drop Statistics Node: 0/3/CPU0 Unresolved drops packets : 0 Unsupported drops packets : 0 Null0 drops packets : 0 No route drops packets : 3 No Adjacency drops packets : 0 Checksum error drops packets : 0 RPF drops packets : 12320 RPF suppressed drops packets : 0 RP destined drops packets : 0 RP/0/RP0/CPU0:router# This happens due to strict IPv6 unicast RPF being enabled on the interface although loose is configured: RP/0/RP0/CPU0:router#show cef ipv6 interface location Wed Sep 3 08:38:47.227 UTC Bundle-Ether2 is up (if_handle 0x00080130) Interface last modified Jan 1 00:10:41, create Reference count 2 Forwarding is enabled ICMP redirects are never sent IP MTU 1500, TableId 0xe0800000 IP unicast RPF check is enabled RPF mode strict <<<<<<<<<<< Protocol Reference count 2 Primary IPV6 local address FE80:748:10::2/128 RP/0/RP0/CPU0:router

Conditions

This can happen when loose IPv6 unicast RPF is configured and we have an IPv6 route for the source of the IPv6 packet pointing at another interface. So these packets should not be dropped since loose IPv6 unicast RPF is configured but they are dropped as strict IPv6 unicast RPF is applied on the interface.

Workaround

Unconfigure and reconfigure loose IPv6 unicast RPF: RP/0/RP0/CPU0:router#conf t RP/0/RP0/CPU0:router(config)#interface RP/0/RP0/CPU0:router(config-if)#no ipv6 verify unicast source reachable-via any RP/0/RP0/CPU0:router(config-if)#commit RP/0/RP0/CPU0:router(config-if)# ipv6 verify unicast source reachable-via any RP/0/RP0/CPU0:router(config-if)#commit RP/0/RP0/CPU0:router(config-if)#end

Further Problem Description