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 (220.127.116.11/28) 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 18.104.22.168 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=22.214.171.124,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.