[libvirt-users] Hypervisor loses network connectivity

[Phill Edwards]

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.

Has anyone else experienced this and know why it happens and how to fix it?
I don't think I fancy rebuilding everything a 3rd time as it seems likely
to happen again. Depending on why it's happening I'm thinking of moving off
CentOS onto Ubuntu as the host OS, or moving away from KVM altogether.

Thanks in advance for any help you can give.
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