[libvirt-users] Hypervisor loses network connectivity

[Michal Privoznik]

On 23.12.2015 03:56, Phill Edwards wrote:
> I have been running KVM on a CentOS 7.1 host for a few months. I have one
> "main" host server plus a "backup" host server. Some time ago everything
> was running fine on "main", but all of a sudden the server became
> non-contactable on it's network interface. I could no longer SSH in and
> therefore couldn't run virt-manager. I don't know what caused this and I
> had to bring all the VMs up on "backup" and they've been running OK there
> ever since.
> 
> Over the last few days I've rebuilt "main" and again all was going well and
> I migrated 4 of the 5 VMs back onto it. Then this morning I came to set up
> the final VM on "main" which is a Sophos firewall machine with 3 NICs (I
> have 3 physical NICs). Nothing uses 2 of the 3 NICs except the Sophos VM. I
> unplugged one of the ethernet cables from "backup" and plugged it into the
> 3rd NIC on "main" and all of a sudden "main" froze and again all network
> connectivity was lost. I rebooted it but the problem still remains that
> it's not contactable over the network and is therefore totally
> non-functional. When I log in at the console and run "ip a" I can see
> various network interfaces including br0 with the expected IP address - so
> it looks like it's got network connectivity but it hasn't.

Sounds like a HW problem to me. guest should not freeze when you
(un-)plug a cable.

Can you bring down a firewall for a while and see if that helps? Plenty
of connectivity issues are caused by firewalls. It that won't help I
suspect clashing subnets/routes.

Michal