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Snow leopard broke my dns

My home network consists of an Airport Extreme connected via ethernet to a fiber / ethernet bridge limited to 100/100 (by the fc/ethernet converter).

After installing snow leopard my dns is broken. Looking from the airport extreme to see which dns servers I received via dhcp and directly doing queries (or ping) to the dns servers works fine. I can also open web pages via ip addresses I receive by directly doing a "dig hostname @dns-server" on the command line.

edit:
Rebooting did not help, but adding opendns nameservers seems to have at least temporarily allowed normal usage.

Message was edited by: dropadrop

iMac C2D, Mac OS X (10.6)

Posted on Sep 2, 2009 8:36 AM

Reply
149 replies

Sep 2, 2009 11:40 AM in response to John Block

That's precisely it.

In Mac OS X Leopard, any user-set DNS settings were used in addition to those specified by a DHCP server, with the user-specified settings taking precedence.

However, in Snow Leopard, if any DNS servers are specified by the user, any DNS server address specified by the DHCP server is not used at all.

The important point here is that DHCP-provided DNS server addresses will not be used in Snow Leopard unless all user-specified DNS servers are deleted.

So if a user has manually specified say, a school or work DNS server or one that is no longer applicable to their network, DNS service will fail in Snow Leopard, where in Leopard the DHCP-specified server would have (eventually) been used after requests to the manually-specified addresses failed.

Sep 2, 2009 12:19 PM in response to dropadrop

I believe there's a bug in Snow Leopard which is causing it to disrespect the DNS hierarchy.

I've also run into DNS problems after upgrading to Snow Leopard. In my DNS settings I saw 3 DNS that were grayed out - which means they are the default DNS servers provided by the DHCP server in my network. Those DNS should be used in the order they are listed with the one in the top having the highest priority. That's where Snow Leopard is failing.

When we removed the last DNS entry from the DHCP configuration (not in the MacBook settings but in the DHCP settings on our DHCP server) and renewed the DHCP lease on the MacBook it fixed the problem. Now I see only 2 DNS entries. When Apple comes out with a fix for this we will put the 3rd DNS back in the list.

Sep 2, 2009 1:04 PM in response to dropadrop

Also experiencing DNS bugginess.
I have a desktop Mac set up here with manual IPv4 config. IPv6 is disabled. A DNS server is on the LAN, and correctly specified in network config. All worked 100% reliably under Leopard.
Since Snow Leopard, DNS sometimes stops working. Ping, http, telnet access to LAN resources will not work, but dig lookups against the LAN DNS server resolve IP's just fine.
Interestingly, I have two DNS servers specified; the second is a DNS proxy that will only resolve internet hosts (i.e. no authoritative zones), and when DNS borks, I can still surf the web - I do NOT get the browser offline mode mentioned at http://forums.macrumors.com/showthread.php?t=777182
Smells very much like a Snow Leopard bug to me - all non-snow leopard hosts on the LAN are fine (various Linux distros, Tiger and Leopard Macs and various Windows versions).

Sep 2, 2009 6:14 PM in response to John Block

Spent an hour or two trying to connect to my school's network after upgrading. The computer teacher had no idea as everything, as he claims, was set perfectly. We were both stumped, until I ran across this thread on one of the school's desktops. Took me less than one minute to clear the DNS settings, and lightning speed internet was at my finger tips. Thanks a million!

Sep 2, 2009 11:31 PM in response to Dogcow-Moof

Thanks for all the replies!

I don't think I had manually entered any DNS servers prior to the upgrade, but I can't say for sure. I did have a static ip-address at my old address (moved two months ago) and I might have added the dns servers at some point.

I do have some addresses from my lan added to /etc/hosts to provide easier access though.

Once I get home I'll verify if I have forgotten any old dns servers in the network configuration.

Sep 3, 2009 1:28 AM in response to TildeBee

Yep, but neither really seems applicable. DHCP on this site hands out the same DNS server settings as I have specified manually, so even if the order was disrespected and it fell back to DHCP-supplied DNS server settings, all should still be fine.

The only preference/order issue that might possibly cause this problem is if Snow Leopard queried the DNS server specified second before the one specified first, i.e. it tried the forwarder before the LAN DNS server. That said, my understanding is that a DNS client will try all the servers in its list until it finds one that can resolve the query, or all DNS servers are exhausted (unless there are bad cache entries, of course, but I have been using dscacheutil to flush the cache to eliminate that possibility).

Snow leopard broke my dns

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