i'm trying to study IPv6 since we're going to use it on our network very soon. i would like to know what STALE means on the output for this show command. appreciate if a link can also be provided. thanks in advance!
Router1#show ipv6 neighbors
IPv6 Address Age Link-layer Addr State Interface
2001:DB8:1:1:C803:17FF:FED4:1D 5 ca03.17d4.001d STALE Fa0/0
FE80::C803:17FF:FED4:1D 5 ca03.17d4.001d STALE Fa0/0
It's a normal part of IPv6 neighbor discovery. Check out RFC 4861, section 5.1.
Basically, the neighbor is no longer known to be reachable (timer expired, no traffic lately, whatever) and reachability will be 'verfied' once traffic is sent to the neighbor again.