[ILUG] Xen bridging problem

[Niall O Broin]

I have a couple of servers at Hetzner running Xen. In each case, the  
dom0 has one public IP, and I have also been allocated a /29 from  
Hetzner, from which I have 5 available IPs. These addresses are  
routed to the respective servers, on which I have Xen VMs running  
which each use one of the IPs.

This works just as I expect it to on both servers, with packets  
addressed to one of the IPs from the /29 landing on the eth0  
interface, and being transferred by Xen bridging to the relevant VM.

However, I have another server at a different provider, with the same  
IP allocation i.e. 1 + 8, and it runs the same OS as the Hetzner  
servers i.e. Debian etch with kernel 2.6.18-1-xen-k7, which is up to  
date.

As far as I can see, the configuration of the dom0sis identical on  
both machines, with the output of   ip a s  being the same except for:

The IP address, of course

The existence of an eth1 interface on the machine whose domUs don't work

The last interface showing  as  16: vif5.0:  on the working server  
and 12: vif1.0: on the non-working, but AIUI that's solely down to  
having stopped and started VMs.


The problem with the other provider's box is that networking doesn't  
work correctly - the domUs can't ping their default routes. Again,  
the configuration of a working domU appears to be the same as that of  
a non-working one. Networking has been setup correctly the provider  
because if I add one of the public IPs to eth0 on the dom0, I can  
acces that IP from the world.

I'm stumped - any ideas?



Niall


P.S. I did ask Unclde Google, and one thing I turned up was this page  
which describes a setup like what I have, IP wise -  http:// 
www.debian-administration.org/articles/360

However, my Hetzner boxes don't use this dummy interface and they  
work just nicely. I did try that dummy interface approach, but it  
didn't work for me either.