This read-only value reports the default lifetime, in seconds, that a Neighbor Binding Table entry keeps under the currently active policy, ranging from 60 to 3600 seconds. It tells an admin how long an IPv6 neighbor binding will be retained before it expires and must be relearned, which affects how quickly stale or disconnected devices drop out of the table. For example, a lifetime of 300 means a binding for a device that goes offline will linger for five minutes before being purged.