Macs sending millions of queries for b._dns-sd._udp

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Macs sending millions of queries for b._dns-sd._udp

I was trying to look at my (non-mac) dns server logs today, and I noticed that four of the mac computers in our network were sending millions of queries for b._dns-sd._udp.0.1.9.10.in-addr.arpa, as well as four other similar addresses. when I say millions, I mean that litterally: in one second I got over 6,000 queries just for those addresses , just from those four machines. Three of the machines are running 10.8.4, the fourth is running 10.6.8

Some reasearch has told me that these queries are tied to Bonjor, and stoping the mDNSResponder service stopped the flood (albeit at the expense of DNS resolution on said machines). Every discussion I have seen on this topic says that these queries are normal, and offers no fix. But over 6,000 queries EACH SECOND is not acceptable, and I don't buy that this volume is "normal behavior"

So what could cause mDNSResponder to go crazy like this? And more to the point, how can I fix it so my DNS servers don't get stress tested every few days?

Posted on Jul 3, 2013 1:16 PM

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Answer 1

Best reply

Linc Davis

Level 10

209,535 points

Jul 3, 2013 1:37 PM in response to Israel Brewster

You can disable Bonjour advertising without also disabling DNS resolution by following these instructions.

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Answer 2

Jul 3, 2013 2:01 PM in response to Linc Davis

Thanks, I'll give that a try if/when it happens again (after restarting mDNSResponder everything looks ok for now, but since I didn't fix anything I rather suspect it will happen again). That said, however, I would prefer an actual fix for the problem rather than just disabling a mis-behaving component, if possible. Of course, if it works and doesn't cause other problems, I won't complain :-)

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Answer 3

Linc Davis

Level 10

209,535 points

Jul 3, 2013 6:07 PM in response to Israel Brewster

Those are unicast DNS service discovery packets. I'm not sure, but you may be able to suppress them by removing your domain from the list of search domains on the clients, or on the DHCP server if applicable; or else by configuring your DNS with the PTR records. See:

files.dns-sd.org/draft-cheshire-dnsext-dns-sd.txt

Manually Adding DNS-SD Service Discovery Records to an Existing Name Server

Men & Mice Support

Bonjour and DNS Service Discovery

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