KVM Networking Hell

Soren Hansen soren at ubuntu.com
Wed Jun 9 21:24:46 UTC 2010

On Wed, Jun 09, 2010 at 02:57:45PM +0100, Jamie McDonald wrote:
> The output of 'brctl show' on the host is as follows
> ## START brctl output ###
> $brctl show
> bridge name     bridge id               STP enabled     interfaces
> br0             8000.001999705a61       no                  eth0
> vnet0
> ## END brctl output ##

I'm not sure if this output got linebroken somewhere. Can you perhaps
make sure the terminal you're using is large enough to hold the output
and put it on a pastebin so we can be sure noone's e-mail application is
messing with the formatting?

> From looking at this it looks like I should have my guest configured
> to use the vnet0 interface instead of br0?

No. vnet0 /is/ your guest. The virtual machines use tap devices for
networking. Think of vnet0 as the host end of the virtual network cable
between the guets and the host. It is meant to be connected to br0 such
that eth0 and vnet0 both are "connected".

> brtables has not been modified in any way.

Ok. And you haven't used Eucalyptus? It's the only thing I know of that
might fiddle with brtables behind the scenes.

What is eth0 on the host, by the way? What kind of NIC?

Soren Hansen
Ubuntu Developer
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