Now this was a very strange situation:

While trying to diagnose a network connectivity problem, there was 1 vista laptop on the network that would connect to the internet, but it couldn’t see any shared drives on the local network.

At first, I thought it was a failing network switch (but network switches rarely fail).

I found out the IP address of the server I was trying to see (192.168.1.101)… DHCP was allocating addresses between 192.168.1.100 and 199).

So, from the laptop, I try ping 192.168.1.101, and I get:

Reply from 192.168.1.108: destination host unreachable

But all the other PCs on the net work (and ping) correctly.

And why does 108 reply instead of 101?

A quick search seems to imply that it can be caused by an odd netmask. But DHCP auto-allocates the net mask, so there cannot be a broadcast address between 100 and 199…

I take a general look around the laptop, and I see its running (drum-roll…) Norton internet security.

Its a new-ish laptop, so this is the trial norton, which expires after 90 days.

So NIS had expired a month ago (around when many network problems started cropping up).

So I figure: I might as well fix this up

uninstall NIS, and install Antivir, winpatrol, bhodemon, spywareblaster.

Once that was over, the network problem just disappeared!

Looks like the norton firewall was seriously stuffed.