mDNSResponder: ERROR: getOptRdata - unknown opt 4

I see the following message showing repeatedly in the /var/log/daemon.log of My Book Live (which seems to be working fine).

$ tail /var/log/daemon.log
Aug 8 21:32:48 [hostname] mDNSResponder: ERROR: getOptRdata - unknown opt 4
Aug 8 21:32:52 [hostname] mDNSResponder: ERROR: getOptRdata - unknown opt 4
Aug 8 21:33:38 [hostname] mDNSResponder: ERROR: getOptRdata - unknown opt 4
Aug 8 21:40:39 [hostname] mDNSResponder: ERROR: getOptRdata - unknown opt 4
Aug 8 21:40:40 [hostname] mDNSResponder: ERROR: getOptRdata - unknown opt 4
Aug 8 21:40:40 [hostname] mDNSResponder: ERROR: getOptRdata - unknown opt 4
Aug 8 21:40:40 [hostname] mDNSResponder: ERROR: getOptRdata - unknown opt 4
Aug 8 21:40:41 [hostname] mDNSResponder: ERROR: getOptRdata - unknown opt 4
Aug 8 21:40:45 [hostname] mDNSResponder: ERROR: getOptRdata - unknown opt 4
Aug 8 21:41:12 [hostname] mDNSResponder: ERROR: getOptRdata - unknown opt 4

Any clue what is causing it? Do you have any suggestion to stop it? Thanks!

Something on your network is doing a mDNS Get Optional Resource Data query with option 4 set. Apparently the DNS responder in the My Book Live doesn’t support that option, and flags it as an error. Since it appears to be doing it quite frequently, you could shut various things on your network down to see what’s doing it.