This feature invalidates next-hop entries for static routes when the next-hop is no longer reachable on directly connected interfaces. This invalidation is based on ARP and Neighbor Cache state information.
When a next-hop is detected as no longer reachable because of ARP/neighbor cache expiry, the route’s next-hop is set as unreachable to prevent the SR from sending continuous ARPs/neighbor solicitations triggered by traffic destined for the static route prefix. When the next-hop is detected as reachable via ARP or neighbor advertisements, the state of the next-hop is set back to valid.