How to use two physical NIC’s inside a Xen guest

1. Show your xen bridge/route script (that actually provides network for domU).
2. What's the difference in tcpdump output on dom0 external interface when you ping host A and gateway from domU ?

"The Xen Networking wiki and the Debian Xen wiki both point me toward using Xen's bridging scripts"

The problem with wikis is that any idiot can edit them -- and they usually do. The Debian Xen wiki page is wrong, so very, very wrong; I don't even have the heart to look at the Xen networking wiki. There used to be useful networky docs in the README.Debian for the xen-utils package, but they seem to have gone walkabout at some stage.

My answer in Bringing up network interface without IP configured in Debian, for XEN dom0 probably won't work for you because it's solving a very different problem. You should probably re-read the question to discover the differences.

That mailing list thread is full of gibberish (and Nabble's usual brain-meltingly stupid formatting) so I'm not going to try and work out exactly where you're seeing a need to put an IP address on both the interface and the bridge, but I can assure you that you don't need to do that -- just an IP address on the bridge will be perfectly sufficient.

The simple way to fix your network config is probably to:

1. Set (network-script network-dummy) and then chattr +i /etc/xen/xend-config.sxp (to discourage you from trying to fiddle with it any more)
2. Delete the br-* stanzas you have currently
3. Delete the gateway line from the eth0:1 stanza
4. /allow_hotplug/d
5. s/eth0/br0/; s/eth1/br1/
6. Add bridge_ports eth0 to your now-br0 config
7. Add bridge_ports eth1 to your now-br1 config
8. /etc/init.d/networking restart