This read-only INTEGER reports the remaining holdtime, in seconds, before this neighbor's cache entry expires if no further UDLD probes are received. An admin cares because an entry with a fast-shrinking lifetime that never refreshes signals the neighbor has stopped sending probes, foreshadowing the entry's removal and a possible link problem. For example, an admin watching this value count down to zero without resetting would suspect the remote device's UDLD process has stopped responding.