I wanted to run a little more recent kernel on this machine (that this thing runs on), and I wanted to run a Debian kernel, to see how that works, on Xen. It went mostly ok, but, with the previous kernel, udev was not being used. When it then for the first time, generated the names for the ethernet interface, it for some reason detected 3 more (nonexistent) interfaces, so the real one ended up as eth4.
That wouldn’t have been that much of a problem, but my iptables specify the interface name, and therefor, it used eth0, and blocked everything, or rather, didn’t let anything in on eth4, of course. Oh well, after solving that (thanks Johannes, for all your help), I locked myself out because I forgot to edit my rules before bringing them back on again. But that was also fixed quickly.
Now then, I wonder if I should play with the fire, and try to make udev do what I want, do a reboot, which, if things doesn’t come back as they should, would mean things will be down until tomorrow, or if I should not.. Since I like to do things Right, and also experiment with things (which to me doesn’t exclude one another), I think I will do that.
What I’ll do is, edit /etc/udev/rules.d/z25_persistent-net.rules, have the interface be named eth0, have the iptables rules not installed on boot, and.. then not forget to edit them, then bring them up (using at(1) of course, to disable them after a few minutes in case it would lock me out, again). So, here we go.