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Fix a DNS resolution failure Network
After upgrading from Leopard to Snow Leopard, my MacBook would randomly stop resolving DNS names on my local network; most often occurring after awaking from sleep. The only way to "fix" this problem was to reboot. To add to the frustration of needing to reboot often, my Mac Mini continued to function without any of these troubles on the same network after being upgraded to Snow Leopard.

Symptoms included pings that would fail, I couldn't point my browser at web sites hosted on local servers, NFS mounts failing, and other general mayhem. Interestingly, while the MacBook was experiencing the problem, I'd run nslookup or dig on the DNS entry in question at a Terminal prompt, and it would return the correct information.

My network has a Fedora 11 box acting as a server with BIND DNS and DHCP running on it. Originally, I'd been publishing both my BIND and internet router as primary and secondary DNS servers respectively via DHCP. After removing the internet router as a secondary DNS, leaving only the BIND DNS, my MacBook magically began to work again.

I don't know the actual root cause and your milage may vary depending on your network setup.
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Fix a DNS resolution failure
Authored by: drudus on Dec 21, '09 08:12:11AM

Directory Service is responsible for maintaining the DNS cache on Leopard & Snow Leopard. Tools like dig, nslookup don't consult the cache, so they could be getting the records from the DNS servers not the cache.

FWIW you can do the following in Terminal to clear the cache - no reboot required.
sudo dscacheutil -flushcache
Admin permission is required.

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Fix a DNS resolution failure
Authored by: Chealion on Dec 21, '09 10:12:12AM
For what it's worth. Directory Services is not in charge of DNS any longer in Snow Leopard. Just Leopard. mDNSResponder took over the heavy lifting of DNS used by most of the system. There's a feature in Snow Leopard that will rearrange the order DNS servers are queried in order to try and speed up DNS requests and avoid the timeout of a DNS request (thereby making the computer look slow). There are a handful of threads on Apple's Discussions Groups and sites like Super User or Server Fault detailing more. Suffice to say,
sudo killall -HUP mDNSResponder
will clear the DNS cache and reset DNS. At my workplace, the removing external DNS servers from being broadcast via DHCP was the only fix (and a non-issue to implement)
Chealion - The one and only! =)
Edited on Dec 21, '09 10:18:51AM by Chealion

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Fix a DNS resolution failure
Authored by: frysco on Dec 21, '09 08:13:40AM
I've seen this exact same issue with 10.6 with both of my machines (Mini and MBP) showing this problem.

Since I'd changed the local DNS settings on the Mini and the DNS server advertised out on DHCP (to the MBP) to be only the BIND on the Mini, I've not had any resolution problems.

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Fix a DNS resolution failure
Authored by: adrian.nier on Dec 21, '09 08:18:34AM

Had the same problem with only one Mac and the same solution.

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Fix a DNS resolution failure
Authored by: bjdraw on Dec 21, '09 09:28:48AM

I've been having the exact same issue communicating with my Windows Home Server on my 13-inch MPB since I updated to snow leopard. Upon further testing I've identified that the server is failing to ARP my Mac's MAC address. I still haven't figured out why, but if I add a static MAC entry on the server, it works.

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Fix a DNS resolution failure
Authored by: SOX on Dec 21, '09 10:12:17AM

I had the same problem in Leopard (10.5). I could get DNS on the shared internet connections to resolve right after boot but then sometime later it would stop. I "fixed" this problem by upgrading to snow leopard (10.6). Now the problem is gone.

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Fix a DNS resolution failure
Authored by: JuanCab on Dec 21, '09 12:08:16PM
I had this same problem after upgrading my MacBook Pro to Snow Leopard (but not by Mac Pro or iMac). I determined that using the campus' DNS server (which is BIND) caused the DNS resolution to go wonky seemingly at random. Pointing to OpenDNS DNS servers fixed the problem on the laptop. I did report this to Apple and even after escalating it several stages and running Apple's diagnostic software for them to collect data from my machine, we could not find the root cause. I suspect some incompatibility between some version of BIND and how Snow Leopard does its DNS caching. See more details on the error in my blog post (look at the section on "Ethernet Issues").

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Fix a DNS resolution failure
Authored by: Dimka on Dec 21, '09 02:31:17PM

I had the same issue on three of my laptops that were upgraded to 10.6 in various places, at home, at my friends house.
I tried the following (with no success)
* Reset my router
* Reset my cable modem
* Disabled WPA/WEP protection
* Changed security protocol from WEP to WPA/WPA2
* Switched wireless channels Ė pick a channel no neighbor is using.
* Turned Airport on & off (via menu or Network preferences)
* Deleted and then recreate/reestablish wireless network connection
* Created a new Network Location
* Made sure your router firmware and Airport card firmware is up to date
* Zaped the PRAM on your Mac (hold Command+Option+P+R on restart)
* Flushed the DNS cache using the Terminal command: dscacheutil -flushcache
* Deleted the and files from ~/Library/Preferences
* Trashed my home directories SystemConfiguration folder and reboot
* Reset my Macís System Management Controller (SMC)

All those steps have helped a bit, but problem remained.
After all it turned out that thorough troubleshooting DNS settings in the routers fixed it.
My conclusion that it is a collective fault of IPS, router makers and Apple, who never tested their stuff well. The problem is really widespread, I found hunderds of calls for help from desperate snow leopard users.

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