[CentOS] network connectivity lost after reboot/upgrade

[Kai Schaetzl]

Gordon Messmer wrote on Mon, 04 Mar 2013 15:29:58 -0800:

> Check your bridge details and make sure that the ethernet device is listed:
>  brctl show
> 
> If those look good, send the content of 
> /etc/sysconfig/network-scripts/ifcfg-{br0,eth0} (or whatever eth device 
> is a member of the bridge).

This is all fine, it's been this way for years. It looks as it always has. No 
errors, collisions, whatever anywhere. TX and RX are about the same.
Just to prove that config is fine I removed the bridge and brought up a 
normal eth0. It's got the same problem. I've never seen such a problem 
before.

The tcpdump shows a lot of arp requests
who-has <IP> tell <IP>
As I understand these are requests for MAC addresses? And tell is the asking 
IP number? In that case there is at least *some* outside connectivity. Most 
of the requests are from the local IP and the IP of the VM, but a few are 
from other machines on the network, including the outbound router. The VM 
runs a monitoring system and these are the clients that want to call in.
Also a few UDP requests (port 1900 and NBT), and that's all.
There are also a few responses to the arp requests, but mostly it's requests. 
Makes sense if it doesn't have much in the arp cache. arp -a lists two 
machines with missing MAC data, that's all.

Kai