xenbr1 dissappeared после перезагрузки сервера

The error message is probably accurate, but there is a better way to do networking. It is recommended to do bridging manually and has even become the default for Xen 4.1+.

You can set up the networking bridges manually on any version of Xen by following:

http://wiki.xen.org/xenwiki/HostConfiguration/Networking

The basic idea (which is different than what you are used to) is that the xenbrN device gets the IP address and the ethN device is used only as a port for the xenbrN device to communicate over.

By following the instructions above you should then disable the bridge scripts in the xend configuration file (/etc/xen/xend-config.sxp).

# (network-script network-bridge)
# (vif-script vif-bridge)