I continue to have weird problems after upgrading my Linux Samba domain controller two weeks ago. Suddenly, today, none of the Windows workstations in the office can get to the Internet. They cannot ping e.g. yahoo.com. The connection info in the lower right says, "No Internet Access". I can RDC into the Windows computers remotely. None of the Linux computers are having this problem. They all connect just fine. I've checked the network interface config on the Windows computers and they look fine - they have the correct IP, DNS and gateway.

The Linux Domain Controller is the DNS server. It is connected to a Sonicwall Firewall/Router.

I've taken down the firewall on the Domain Controller.

What could possibly be going on with this network?

Since they have the correct IP, DNS, and Gateway, could it be an IPv4 vs IPv6 thing? Even if all of the IPv4 config is correct, maybe something funny's going on with IPv6 and the Windows computers are trying to use IPv6 only or something.

Wow! I found the problem. The other evening one of my network switches was flaking out so I replaced it. I couldn't find another switch, so I grabbed a spare Linksys router thinking I would just use the switch ports. As it turned out, the configured IP address in that router was the same as the SonicWall firewall, which is also the external DNS server. Once I pulled the Linksys out of the system the Windows computers could connect to the Internet. I have no idea why the Linux computer could connect to external domains.