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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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