KVM Networking Hell

Soren Hansen soren at ubuntu.com
Tue Jun 8 22:31:03 UTC 2010

On Tue, Jun 08, 2010 at 10:49:04PM +0100, Jamie McDonald wrote:
> #### START /etc/network/interfaces on HOST ####
> auto eth0
> iface eth0 inet manual
> auto br0
> iface br0 inet static
>         address
>         network
>         netmask
>         gateway

I probably doesn't matter, but that address with that netmask doesn't
give that network.

> auto eth0
> iface eth0 inet static
>     address
>     netmask
>     network
>     broadcast
>     gateway

This adds up, though :)

> Symptoms
> ----------------
> I can now ssh from the host into the guest (from the host) and from the
> guest to the host, however try as I might I cannot get the guest to access
> the outside world or the host to pass packets to the guest.

It is not the job of the host to do any of this, really.

> As you can see, the bridge is working and when I start the VM from
> virsh# the vnet0 adapter is created, however no tap0 is being created.

vnet0 is the tap device. This is the expected behaviour.

> As far as I am aware you should not need ipv4 forwarding enabled in
> the Kernel for bridged networks

That's correct.

> If any of you could shed any light on this issue (since I can't seem
> to find anyone else with the issue) it would be most appreciated.

Off the top of my (arguably quite tired) head, it looks good. Can I see
the routing table in the guest?

Soren Hansen
Ubuntu Developer
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