You can configure the duration (in seconds) that a router considers a remote IPv6 node to be reachable.
Router advertisement messages include a reachable time value. All nodes on a link use the same value. By default, the reachable time duration is 0.
Extreme recommends that you configure a long duration, because a short duration causes IPv6 network devices to process the information at a greater frequency.
device(conf-if-eth-0/1)# ipv6 nd reachable-time 600
Note
The actual reachable time ranges from 0.5 to 1.5 times the configured or default value.