[CentOS] network connectivity lost after reboot/upgrade

Mon Mar 4 18:15:46 UTC 2013
Kai Schaetzl <maillists at conactive.com>

I upgraded one of my old machines running 5.x to the latest kernel (from 
308.24.1 to 348.1.1).
After rebooting network connectivity was gone. I rebooted with the old 
kernel, I also tried the one before it (308.20.1) still no luck. So I 
assume it's got nothing to do with the kernel or even CentOS. But a 
hardware failure seems also unlikely, see below.

ethtool shows the link as up and if I remove the cable as down.
I attached a laptop via crossover cable, it detects the link, but same 
problem.
I disabled iptables and set selinux to disabled. No change.
There's a Xen VM running on that machine and I can ping it from the 
hardware. So, internal networking seems to be ok. I'm using bridged 
networking for Xen connectivity, setup by normal Red Hat means, not via 
Xen. Never had a problem.
There are no errors in the logs, except for dhcpd telling network is down 
and named is also giving some weird errors. This is my only dhcpd, so I 
would like to have it up ASAP :-(

Is there anything else besides a weird hardware failure that I could 
check? I'm going to get a new card tomorrow and see if that changes the 
situation. This is mobo internal networking based on nforce-MCP61.

Has anyone seen such a hardware failure where the link goes up but no 
packets go over the wire? It seems a bit unlikely that this hardware 
failure (and nothing else) should happen on a reboot after an upgrade.

Thanks.



Kai