As mentioned in previous blog posts, DNS in Snow Leopard behaves differently than with previous versions of Mac OS X. One of the biggest changes is that DNS server entries aren’t always followed in strict order, and if a DNS server is temporarily unresponsive it gets moved to the end of the search order. This can cause confusion when troubleshooting DNS issues, as the DNS servers list obtain from DHCP or set locally isn’t always what-you-see-is-what-you-get.
Apple has introduced the ability in Mac OS X 10.6.3 to allow you to adjust this DNS search order behavior, giving you the ability to turn strict order searching on. Activating this feature requires editing the com.apple.mDNSResponder.plist file and restarting the mDNSResponder daemon. Instructions for how to do this have been posted to Apple’s Knowledgebase article HT4030. http://support.apple.com/kb/HT4030