[CentOS-virt] Emergency help needed on host network randomly stop working.

Wed Oct 12 16:28:48 UTC 2011
Eric Searcy <emsearcy at gmail.com>

On 10/12/11 12:43 AM, Magicloud Magiclouds wrote:
> Hi,
>   This is a Centos 5.5 host with one xen guest.
>   About 2 weeks ago, the host randomly lost network connection. By
> this I mean I could not connect to the services on it, or ping it.
> Also was the status of the guest.
>   From serial console, I connected to the host, trying to see what
> happened. No clue (any error messages) in messages or dmesg.
> ifdown/ifup the interface did not help, either. Only rebooting was my
> only choice.
>   Searching through Google, I got the information that some other guys
> met similar problem, and resolved by setting stp on with the bridge
> interface.
>   I set it, too. And the problem still occurs.
>   Any idea what I should check now?
>   Thanks.

When outage occurs, from the host these might be good things to look at
and/or share with the list:

ip link
brctl show
arp -n (arp -n from your next-hop router too)
tcpdump -ln -i peth0 (try some activity; e.g. ping out to router, ping
in from router)
tcpdump -ln -i br0 (more activity)

Depending on your xen bridge setup the bridge might be named eth0 or
virbr0; peth0 might be different too.