# NDP Status

The [RFC 4861](/glossary/rfc/4861) defines a number of statuses:

^ Status ^ Description ^ Comment ^
| `INCOMPLETE` | Address resolution is in progress and the link-layer address of the device has not yet been determined. | |  
| `REACHABLE` | Device is known to have been reachable recently (within tens of seconds ago). | |  
| `STALE` | Device is no longer known to be reachable but until traffic is sent to the neighbor, no attempt should be made to verify its reachability. | |  
| `DELAY` | Device is no longer known to be reachable, and traffic has recently been sent to the neighbor. Probes should be delayed in order to give upper-layer protocols a chance to provide reachability confirmation. | |  
| `PROBE` | Device is no longer known to be reachable, and unicast [Neighbor Solicitation](/glossary/n/neighbor_solicitation) probes are being sent to verify reachability. | |