DNS fails to resolve w/ 10.6.8

Question

I have a home network consisting of 2 iMacs and 1 Macbook Pro, all running on 5 GHz N-band through an Asus RT-N56U dual-band router. The Macbook Pro and one of the iMacs are fine, however starting several months ago the third iMac began having a problem where it fails to resolve domain names, as many as 3 times a day. All 3 computers have identical network preferences, each with their own static LAN IP.
I looked through the Console logs for the problem iMac and found the same entries repeating, which appear to show mdnsResponder crashing:
mDNSResponder[18]
SendResponses: No active interface 0000000000000006 to send: 0000000000000000 08   41 _afpovertcp._tcp.local. PTR User's\032Computer._afpovertcp._tcp.local.
mDNSResponder[18]
SendResponses: No active interface 0000000000000006 to send: 0000000000000000 08   34 _rfb._tcp.local. PTR User's\032Computer._rfb._tcp.local.
mDNSResponder[18]
ERROR: handle_resolve_request bad interfaceIndex 6
com.apple.usbmuxd[37]
_BrowseReplyReceivedCallback (thread 0x7fff70463cc0): Error doing DNSServiceResolve(): -65540
mDNSResponder[18]
SendResponses: No active interface 0000000000000006 to send: 0000000000000000 04   15 User's\032Computer._device-info._tcp.local. TXT model=iMac10,1
/System/Library/CoreServices/Finder.app/Contents/MacOS/Finder[102]
BonjourBrowser::DNSServiceQueryRecord returned -65540
mDNSResponder[18]
ERROR: handle_resolve_request bad interfaceIndex 6
com.apple.usbmuxd[37]
_BrowseReplyReceivedCallback (thread 0x7fff70463cc0): Error doing DNSServiceResolve(): -65540
mDNSResponder[18]
SendResponses: No active interface 0000000000000006 to send: 0000000000000000 04   15 User's\032Computer._device-info._tcp.local. TXT model=iMac10,1
mDNSResponder[18]
SendResponses: No active interface 0000000000000006 to send: 0000000000000000 08   34 _rfb._tcp.local. PTR User's\032Computer._rfb._tcp.local.
mDNSResponder[18]
PenaltyTimeForServer: PenaltyTime negative -154358, (server penaltyTime -58278099, timenow -58123741) resetting the penalty
mDNSResponder[18]
ERROR: handle_resolve_request bad interfaceIndex 6
com.apple.usbmuxd[37]
_BrowseReplyReceivedCallback (thread 0x7fff70463cc0): Error doing DNSServiceResolve(): -65540
mDNSResponder[18]
ERROR: handle_resolve_request bad interfaceIndex 6
com.apple.usbmuxd[37]
_BrowseReplyReceivedCallback (thread 0x7fff70463cc0): Error doing DNSServiceResolve(): -65540
mDNSResponder[18]
mDNSResponder mDNSResponder-258.21 (May 26 2011 14:40:13) stopping
mDNSResponder[18]
mDNSResponder mDNSResponder-258.21 (May 26 2011 14:40:13) starting
I did some Googling on the issue and came up with results similar to my problem, dating back as far as OS X 10.6.5, perhaps even earlier. Several people suggested killing/restarting mdnsResponder as a temporary fix using the following:
sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist
sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist
This appeared initially to be successful, however it turns out the fix is just that – temporary. DNS still breaks every day, leaving my iMac able to send and receive email, but unable to browse the Internet.

Answer 1

Hi,
Regarding search domains - those are not directly responsible for your internet conectivity.
You can read what they are here:
http://support.apple.com/kb/HT4845
regarding the mdnsResponder
You can try dragging this file to the desktop & rebooting.
Machintosh HD/System/Library/LaunchDaemons/com.apple.mDNSResponder.plist
This should clear the issue.
Please let me know how it goes.