[Fedora-xen] xenbr0 failure when changing motherboard

[Evan Lavelle]

I've just asked this on the xen list, but I suspect it may be an 
aliasing problem on Fedora 8, so I though I'd ask here.

I have a production system (ie. I can't upgrade it) which has an F8 Dom0 
with various DomU's (the Dom0 is kernel 2.6.21-2952, with Xen 
3.0-x86_64). I needed to change the motherboard, so I just moved the 
drive to a new motherboard.

Amazingly, everything works, apart from one problem. I had to change the 
guest configs to use virbr0 rather than zenbr0 (in the vif line in the 
old-style config file).

The problem with virbr0 is that I've now got a local subnet; the domU's 
can see out, but I can't see into the DomU's from the network. The 
previous (xenbr0) setup was that the DomU's got an IP address from an 
external hardware router, and everything was on the same 196.168.1 subnet.

Now, I could presumably fix this through a libvirt setup, but I want to 
change as little as possible, and the DomU's don't currently use libvirt 
configuration files. So, if possible, I'd like to go back to the xenbr0 
setup.

When I try to boot with a xenbr0 setup, I get:

> Error: Device 0 (vif) could not be connected. Could not find bridge device xenbr0.

What I think has happened is that the existing fc8-xen on my hard drive 
is confused about the network hardware on the new motherboard (a Dell 
R200 server). When the new board originally booted up, networking was 
disabled, but I fixed this by aliasing eth0 to eth3. The (old) driver 
seemed to have identified the new NICs at eth3 and eth4, rather than 
eth0/1. Anyway, that fixed the network on Dom0, but it seems to be 
giving Xen a headache when it boots any DomU's.

I know that F8 had problems in the network-bridge script related to 
aliasing, but network-bridge runs without producing errors, so I'm not 
convinced that that's the problem here.

Any thoughts?

Thanks -

Evan