Some debugging ideas
add the line: set -x to the network scripts that you are using (i.e. network-brige, vif-bridge) This will produce output in /var/log/syslog
configure udev log DEBUG in /etc/udev.conf
keep an eye on xenstore with xenstore-ls and xenstore-read to see if the vif devices are being created.
Make sure that the vif and veth devices exists
Keep an eye on all the logs in /var/log/xen/
try to use strace on different commands, scripts, entry points to see where things hang etc.
Some debugging ideas
add the line:
set -x
to the network scripts that you are using (i.e. network-brige, vif-bridge)
This will produce output in /var/log/syslog
configure udev log DEBUG in /etc/udev.conf
keep an eye on xenstore with xenstore-ls and xenstore-read to see if the vif devices are being created.
Make sure that the vif and veth devices exists
Keep an eye on all the logs in /var/log/xen/
try to use strace on different commands, scripts, entry points to see where things hang etc.