Device(config-if)# ipv6 nd nud retry 1 1000 3 1000
Configures the number of times neighbor unreachability detection (NUD) resends neighbor solicitations (NS) before the final wait time on the last probe and the interval between NS during NUD.
When a device runs NUD to resolve the ND entry for a neighbor, it sends three NS packets 1 second apart. In certain situations (for example, spanning-tree events, high traffic, the end host being reloaded), three NS packets sent at an interval of 1 second may not be sufficient. To help maintain the neighbor cache in such situations, use the ipv6 nd nud retry command to configure exponential timers for NS retransmits.
The retransmit probe time is calculated by tm^n (where, t = interval, m = base, and n = current
attempt). Therefore, ipv6 nd nud retry 3 1000 5 command will produce
retransmit intervals of
1,3,9,27,81 seconds. If the final-wait-time is not configured, the entry
remains for 243 seconds before it is deleted.
- The range for base is from 1 to 3.
- The range for interval is from 1000 to 32000 milliseconds.
- The range for max-attempts is from 1 to 128.
- The range for final-wait-time is from 1000 to 32000 milliseconds.
Device(config-if)# ipv6 nd cache expire 7200
Configures the length of time before an IPv6 neighbor discovery cache entry expires. The range is from 1 to 65536 seconds.
By default, an ND cache entry is expired and deleted if it
remains in the STALE state for 14,400 seconds, or 4 hours. The
ipv6 nd cache expire command allows the user to vary
the expiry time and to trigger autorefresh of an expired entry
before the entry is deleted.
When the refresh keyword is used, an ND cache
entry is autorefreshed. The entry moves into the DELAY state and
the NUD process occurs, in
which the entry transitions from the DELAY state to the PROBE state
after 5 seconds. When the entry reaches the PROBE state, a neighbor
solicitation (NS) is sent and then retransmitted as per the
When you configure the expiry duration, the device will probe the neighbor on entry expiration, that is, the neighbor discovery enters into the probe state and sends a neighbor solicitation to the neighbor. If the neighbor responds, the ND cache entry reverts to the reachable state. If the neighbor does not respond, the cache entry is deleted.
This maintains an entry in the ND cache until the neighbor exists and is reachable, even if no traffic is sent to the neighbor.
ipv6 nd na glean|
Device(config-if)# ipv6 nd na glean
Configures ND to glean an entry from an unsolicited neighbor advertisement (NA).
The IPv6 ND ignores an unsolicited NA packet if it does not have a cache entry for the neighbor that is sending the NA. If the ND is configured on an interface to glean an entry from an unsolicited NA, the neighbor discovery protocol creates neighbor discovery cache entries based on unsolicited NA packets sent from the previously unknown neighbors on that interface. This allows the device to populate its ND cache with an entry for a neighbor in advance of any data traffic exchange with the neighbor.