[CentOS] my notes on bond, bridge, network, kvm, host and virtual so far

Wed Feb 8 03:26:33 UTC 2012
Devin Reade <gdr at gno.org>

I have no idea if this is the source of your problem (I wasn't using
bonded interfaces), but it's sufficiently similar that you might
want to try it.

I had a lot of problems with the network stack on VMs, both under
VMWare ESXi and Xen where the network would just go numb.  After a
lot of splunking I determined that it seemed to be related to 
faulty TCP segment offload.  Generally speaking, between the VM,
the virtual NICs, the hypervisor/host, and the physical network card, 
some levels figured that they'd offload segmentation handling to 
a lower layer, the lower layer wasn't doing it, and the upper layer
thought that it was.

Under low network load everything seemed fine but as the network
got pushed things would blow up and go numb.

Turning off TSO in the VM seemed to do the trick, although I think
in the Xen case I turned it off in the host as well.

The basic command is:  /sbin/ethtool -K ethX tso off

While I had the above command in rc.local, I would also run the
attached script in /etc/cron.hourly as there were some circumstances 
where tso would get reenabled.

Good luck

Some people are like Slinkies: Not really good for anything, but you can't
help but smile when you see one tumble the stairs.
					- Anonymous