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Re: [Xen-users] xen network interfaces: How do I retrieve from an executable running within domain0 the MAC of an frontend-(domainU)-network-interface ?

On Sun, Aug 23, 2009 at 6:22 PM, Kay Schubert<kayegypt@xxxxxx> wrote:
> Now each of those backend-interfaces gets assigned the
> infamous FE:FF:FF:FF:FF:FF MAC. That turns out to be a problem if I try to
> send packets from domain0 through the bridge-interface to any of the domainU
> instances: the log tells me something along "ethernet source and target are
> equal, can't send packets to myself".

I had that problem on some dom0s as well :)
Interestingly it doesn't occur when I split dom0 and domUs traffic on
separate physical interfaces. For example :
- eth0 for dom0's IP address
- eth1 setup as trunk, created vlans and bridge on top of vlans, no IP
address on those bridges, with domU using the bridges.

> However, I had some success when I
> manually assigned (by calling at domain0, for instance, "ip link set vif13.1
> address 00:16:3E:7D:D0:98") the MAC assigned to the
> frontend-(domainU)-interface to the backend-(domain0)-interface as well.

Actually, it doesn't matter what MAC you assign to the vif, as long as
it's unique. At least that was the case on my setup. So I simply
modify /etc/xen/scripts/vif-bridge, and generate a random MAC for
every vif. It's not the same as domU's MAC.

> Now my question is: Supposed an executable is running within domain0, and this
> executable has been handed the name of a Xen backend interface, is there a
> way to obtain the MAC of the associated frontend-(domainU)-interface ?

If you still need domU's mac (for any reason), you could try this
- xm network-list 13
- xenstore-ls /local/domain/13/device/vif

where "13" in that example is domU's ID. You could usually find out
domU id from vif name (in your case vif13.1). I haven't tried running
it from vif-bridge script though.


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