What No resolv.conf?
In Mac OS X, although it has a /etc/resolv.conf, it doesn’t seem to use it. So although I have a local network, and a local DNS to resolve my local hosts, I was not able to ping anyone!
See, when I do a dig on “spanky” it resolves correctly using the local DNS. But when I ping (or use any other application that does an nslookup) it fails. I believe this is because dig goes straight to the DNS, while other applications attempt to use multicast. This bypasses resolv.conf completely.
To make Mac OS X use the search domains and DNS that are in resolv.conf, I had to add them in the Network control panel. Look in TCP/IP for the DNS and Search domains sections, and this should do the same trick you used to use resolv.conf for!