Sometimes you may need to do a DNS flush, say after a mysterious DNS network issue. Here are the commands.
Mountain Lion / Lion sudo killall -HUP mDNSResponder
Leopard sudo dscacheutil -flushcache
Tiger lookupd -flushcache
Windows ipconfig /flushdns
Run a nslookup or ping to check if you are indeed getting the correct IP(s) from the DNS server(s).