As mentioned before, I disabled xen before the etch->lenny upgrade. Now I’ve re-enabled xen, and the following bits may be of wider interest:
My server at the Hetzner hosting center has one static IP address and a small network that is routed towards that IP address. So my plan was to use this small network (88.198.160.176/28) for the virtual switch inside the xen Dom0 and connect all the domUs to it. I solved this the following way:
In /etc/network/interfaces I tell Debian to create the bridge and use br0 as the interface of the dom0 into that bridge:
auto br0
iface br0 inet static
pre-up brctl addbr br0
address 88.198.160.177
netmask 255.255.255.248
bridge_fd 0
bridge_hello 0
bridge_stp off
That way, the xen scripts themselves have little to do. The settings in /etc/xen/xend-config.sxp are:
(vif-script 'vif-bridge bridge=br0') (network-script network-route)
In the config-file for each individual domU, I just use something like
vif = [ 'ip=88.198.160.178,mac=00:16:3e:77:e2:79,bridge=br0' ]
but I’m not sure whether that’s actually needed at this point.
Concerning the domUs: The hints in the Debian Wiki were helpful, especially about changes to the console handling.