Enhanced IPv6 Neighbor Discovery Cache Management
Neighbor discovery protocol enforces neighbor unreachability detection, which can detect failing nodes or devices, and the changes to link-layer addresses. Neighbor unreachability detection is used to maintain reachability information for all the paths between hosts and neighboring nodes, including host-to-host, host-to-device, and device-to-host communication.
The neighbor cache maintains mapping information about the IPv6 link-local or global address to the link-layer address. The neighbor cache also maintains the neighbor's reachability state, which is updated using neighbor unreachability detection. Neighbors can be in one of the following five possible states:
DELAY: Neighbor resolution is pending, and traffic might flow to this neighbor.
INCOMPLETE: Address resolution is in progress, and the link-layer address is not yet known.
PROBE: Neighbor resolution is in progress, and traffic might flow to this neighbor.
REACHABLE: Neighbor is known to be reachable within the last reachable time interval.
STALE: Neighbor requires resolution, and traffic may flow to this neighbor.
Use the ipv6 nd na glean command to configure the neighbor discovery protocol to glean an entry from an unsolicited neighbor advertisement.
Use the ipv6 nd nud retry command to configure the neighbor discovery protocol to maintain a neighbor discovery cache entry for a neighbor during a network disruption.
Use the ipv6 nd cache expire refresh command to configure the neighbor discovery protocol to maintain a neighbor discovery cache entry even when no traffic flows to the neighbor.