DHCP server as a DDNS forwarder

Another interesting case today: After an IP address renewal, some printers’ FQDNs could no longer be resolved. This was a random occurrence, although some printers were affected more than others.

It turns out that once in a while the queues on the DHCP server get full and the DNS server never gets the information that the records need to be refreshed.



Turning on DDNS manually on the printer and flapping the printer port seems to help.


@update April 11, 2018

Actually, this was caused by two hosts that went haywire and sent DHCP requests with empty hostnames. The Bluecat server v8.1.1 is still vulnerable and its DDNS process crash when it receives such requests. The requests were sent every minute by two hosts, so the process crashed twice per every minute.

Troubleshooting method:

  • find dhcp ”top talkers”
  • analyse the error logs on the dhcp server





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