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Symptom:


I see this in my BIND DNS Server logs over and over....  

01-Jan-2010 15:23:17.331 queries: info: client 192.0.2.16#5353: query: b._dns-sd._udp.0.2.0.192.in-addr.arpa IN PTR +
01-Jan-2010 15:23:17.332 queries: info: client 192.0.2.16#5353: query: b._dns-sd._udp.0.2.0.192.in-addr.arpa IN PTR +
01-Jan-2010 15:23:17.346 queries: info: client 192.0.2.16#5353: query: b._dns-sd._udp.0.2.0.192.in-addr.arpa IN PTR +
01-Jan-2010 15:23:17.385 queries: info: client 192.0.2.16#5353: query: b._dns-sd._udp.0.2.0.192.in-addr.arpa IN PTR +
01-Jan-2010 15:23:17.386 queries: info: client 192.0.2.16#5353: query: b._dns-sd._udp.0.2.0.192.in-addr.arpa IN PTR +
01-Jan-2010 15:23:17.401 queries: info: client 192.0.2.16#5353: query: b._dns-sd._udp.0.2.0.192.in-addr.arpa IN PTR +
01-Jan-2010 15:23:17.402 queries: info: client 192.0.2.16#5353: query: b._dns-sd._udp.0.2.0.192.in-addr.arpa IN PTR +


Hundreds and hundreds of queries like this at a time.  
 
Can you explain?

Problem:

Machines with Zeroconf enabled are trying to do DNS Service Discovery.

These are queries generated by 'Multicast/Unicast DNS Service Discovery or 
Zeroconf', which is a service of Apple 'Bonjour/Rendevous' or Unix Services like
'Avahi'. DNS Queries coming from Port 5353 are DNS queries from a Zeroconf service.

The DNS Service Discovery enabled clients are looking for pointers to services
running in their network block 192.0.2.0/24.

This is harmless. If there is not PTR record for the requested ownernames, it
only means that unicast Zeroconf is not configured.

If you want to utilize DNS-SD, there is additional information at http://www.dns-
sd.org/
and a very good book on the subject from Apples Stuard Chesire and Daniel
Steinberg called 'Zero Configuration Networking: The Definitive Guide' (http://
http://www.oreilly.de/catalog/9780596101008/).

Zeroconf is a quite interesting technology if you have MacOS X and/or Unix/Linux
machines in your network.
 

Solution

No solution needed, however the requested PTR records can be added to DNS to utilize DNS Service Discovery (DNS-SD)