I had an ongoing problem with a customers network.

He had 2 PCs (XP home and XP pro), and in sharing folders, the pro pc could see the home shares, but the home PC could not see the XP shares… the pro pc would show up under “my network places”, but when trying to view the folders, I got the usual “you might not have permission to use this network resource”.

I tried all sorts of tricks to make it work. The workgroup was the same, I created an identical admin user on both PCs… It should have worked.

A few months later, this customer bought a third PC (vista home premium). I setup the network shares for this as well, and I get a similar issue: the vista and “XP home” shares are visible by all PCs, but the XP pro shares are only visible by the pro PC itself.

After a lot of digging around, I find some evidence that Link Layer Topology Discovery (LLTD) Responder (KB922120) could fix the problem. So I install it to the pro PC, but it has zero effect.

The error messages from vista a slightly more descriptive than those from XP… and I start to suspect a firewall problem.

I take a look at the XP firewall on the XP pro pc, but it all looks normal. Nothing unusual being blocked.

I disable the firewall, and suddenly the shares on the pro pc are visible by the other PCs…

OK, hit the advanced -> restore defaults, and the XP firewall is back to behaving normally.

Who would have thunk it?