I believe that Xen 4.1 saw the rewrite of what I’m assuming is the entire network configuration stack. Perhaps the most significant thing for me was that the domU’s network connection isn’t created/initiated properly if the domU config file has anything other than the MAC address and the bridge to which to attach the vif to.
Which meant that my test domU didn’t have a working connection. Oh, it appeared on both systems. Dom0 had a vif1.o show up, and the domU had a eth0 show up. Just that… ifup eth0 would timeout. But removing the ‘network-script=bridge’ component from the domU config file and restarting the domU got the network connection up and running again.
So I have to remember this for when I upgrade the rest of my domUs.