Re: [Xen-users] certain mac addresses don't work

[Florian Mayer <lists@xxxxxxxxxxxxxxx>]

Patrick Kaeding schrieb:

> Hello
>
> I recently noticed a weird problem I was experiencing in my xen setup.
> I'm actually not sure if the problem was with Xen, or with linux
> bridging, but I want to let everyone here know, in case others have
> the same problem.
>
> My dom0 is running Xen3.0.1 on Ubuntu 5.10, with two physical nics. 
> One nic, eth0 is for management, ssh access to dom0, nfs traffic, etc.
> The other nic, eth1, is for all domU traffic.  It is in promisc.
> mode, passing all traffic to the bridge, xenbr0.
>
> The problem I was experiencing was that some domUs would not be able
> to get through to the outside.  I ran tcpdump on eth1, xenbr0, and
> vif1.1 (or whatever the appropriate vif was for the domain in
> question).  The packets would appear on vif1.1, but not xenbr0 or
> eth1.  However, some domUs would work fine, and their packets would
> show up on all three appropriate places.
>
> I traced the problem to the MAC addresses.  I need to specify mac
> addresses for overall management on the greater network, but it
> doesn't matter (to me or the network admin) what they are, as long as
> they are unique on the network.  It turns out that addresses starting
> with 11:13 - 11:17 don't work.  (There are probably other ranges that
> don't work, but that is all I tested.)  According to
> http://standards.ieee.org/regauth/oui/oui.txt those addresses are not
> assigned (though they are also not reserved for private use, or for
> Xen), and I know that they are not in use on my network.  I changed
> the MAC addresses for the hosts that didn't work to a range that I
> know works, and everything is fine.
>
> Does anyone know why this happened?
>
> In any case, I hope this info can save some other people a few headaches.
>
> -Patrick
>
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Did you try tcpdump -vv ?? You will see a lot of checksum errors.

I had other very very weird problems with XEN networking in 3.0.1 and 
3.0.2 (also with Ubuntu 5.10) It is a bug in xen. The current 
workarround is entering
ethtool -K eth<0-n> tx off in each domU for each available interface.

I did it automatically by writing
post-up ethtool -K eth0 tx off into /etc/network/interfaces of each domU.

Maybe this will work for you too.

Regards
Flori

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