On my Debian Xen system the logs are in following directory.
You may like to check that or use netstat or some thing like that to find out where connections are going on.I had a similar problem not exactly as you are facing I was able to see my lan card up in my Dom0.
But network was unreachable.Doing an ifconfig showed the ip.
After some hit and trials I found that plugging the physical connection to a different lan card solved this issue.May not be the case with you but you may try.Sounds silly but it worked for me when I gave IP to my Dom0 it was by default activating eth2 and not eth0 as I expected it to.
There is a utility known as strace you may try to diagnose it.
There is a tool known as dtrace
See if this can help you.
You may not need the following but just in case.
See if the following tools do help you any how
Try to do some network activity from your network card which is recognized by dom0.
I use Debian in that the settings are in
/etc/network/interfaces this is how the interfaces file look like
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
# The loopback network interface
iface lo inet loopback
iface eth2 inet static
If you have physical access to the box then
there is a live CD from Citrix Xen for free you can down load and use just an idea.It may help you do to any sort of change debug the problem.
what ever architecture you have just try to use it rather than changing the original system.If you do solve the problem do post here.
I mentioned above I found this useful in your context
Not really but sort of. 802.3ad will attempt to push all the
traffic from a single session over a single link to avoid reordering.
If you start multiple sessions over the links from a single system
it should use both (though again, it will probably start with both
sessions on a single link). It's also been my experience that many
vendors ignore that "all sessions on a single link" thing and will
spill over. I have done more than 1Gbit/s between two Windows
systems with dual Intel NICs on a single session.
Let me know if it works or even if it does not.