On Dell PowerEdge 1950 and 2950 hardware the built-in network interfaces have always been detected backwards under Red Hat Enterprise Linux 4. The NIC labeled “1” is eth1, the NIC labeled “2” is eth0. Okay, no problem, we were able to figure that out and compensate. It isn’t hard to reverse the cables.
The latest Red Hat Enterprise Linux 4 kernel patch (2.6.9-55.0.2, maybe 2.6.9-55, too) fixes the detection on 2950s.
So when you patch and reboot, your cable is suddenly in the wrong port.
Found that out the hard way about 30 minutes ago on a machine 82.3 miles from me. Luckily I had two cables on this machine, and my network engineers just swapped the port configurations.
Just another example of Red Hat changing the behaviour of a shipping product mid-lifespan. I saw nothing in the release notes about this, either. Grrrr.
Ick, doesn’t look like it’s in the release notes.
kbase article here http://kbase.redhat.com/faq/FAQ_46_10460.shtm