Here I was, earlier today, simply trying to swap the default gateway of the Ethernet card of my Windows 7 box, and ran into the following peculiarity. First off, as soon as I swapped the gateway, my Ethernet connection went down. To investigate this, I popped into the command-line and tried pinging the new gateway only to run into the error message below:
I tried pinging the older gateway and got the same error. I tried pinging any node on my network and got the same error. What's more, when I swapped the gateway back to the older one, everything went back to being fine and dandy. Odd, eh?
The fact that it failed only with a different gateway more or less ruled out hardware issues. When I tried doing the same thing with a different box (Kubuntu), it went off without a hitch. So, it was endemic to this particular Windows 7 PC. What could it be?
It hit me a while later - while I was mucking about with what I knew were exercises in futility - that I was not going about this methodically enough. While debugging hardware issues, it is always important to list all the key players involved and keep things as simple as possible and then build one's way up to situations of greater complexity. I, being the dolt that I can sometimes be, had completely forgotten about the bleeding Windows Firewall.
Off I went and turned it off via the control panel and all was peachy once again. Pings went through and my connection was back up. I don't recall ever having messed with the Firewall, but it is quite possible that I did. Later, rather than turning the damn thing off, I realised that resetting the Firewall to its default settings also did the trick just as well. This can be done by clicking on the Restore defaults link on the left hand side of the Windows Firewall control panel.
I don't know what kind of nefarious rule would cause such a restriction. But I hope this helps somebody out there :)