The networkbridges are configured via different skripts depending on the virtualization technology to be used.

XEN

For XEN the default bridge skript is /etc/xen/scripts/network-bridge. The call syntax is as follows:

    /etc/xen/scripts/network-bridge start|stop|status|restart [vifnum=[0-9]+] [bridge=bridgename] [netdev=networkdevice]

This skript works for all network interfaces except VLANs.

In order to restart bridge xenbr0 use /etc/xen/scripts/network-bridge restart bridge=xenbr0 with all other parameters as optional.