Would someone elaborate a bit on these log entries? This is saying the next hop server is down because of failure to register? What might cause a registration failure? In this particular case the other side (also a Cisco router) had no corresponding log entries.
UPDATE 2: When running NHRP over GRE tunnels, it seems that if the underlying medium causes dropped packets, this can lead to this problem (as the registration packets are dropped). Not sure if that's the cause in this circumstance, but we recently have come across a situation with a bad link which consistently has caused nhrp registration failures.
UPDATE: there were no other relevant log entries around these 2 lines; nothing that would suggest a connectivity issue or other problem. Also, the dmvpn tunnel is normally fine, this was just a brief hiccup.
Log entries:
005495: Aug 27 02:01:51.471 utc: %DMVPN-5-NHRP_NHS_DOWN: Tunnel1000: Next Hop Server : (Tunnel: 10.23.72.1 NBMA: 22.22.22.22 ) for (Tunnel: 10.23.73.17 NBMA: 33.33.33.33) is DOWN, Reason: NHRP Registration Failure(NHRP: no error)
005496: Aug 27 02:01:51.548 utc: %DMVPN-5-NHRP_NHS_UP: Tunnel1000: Next Hop Server : (Tunnel: 10.23.72.1 NBMA: 22.22.22.22) for (Tunnel: 10.23.73.17 NBMA: 33.33.33.33) is UP
