[root@xenmaster003 xen]# cat /etc/xen/scripts/an-network-script
#!/bin/sh
dir=$(dirname "$0")
"$dir/network-bridge" "$@" vifnum=0 netdev=eth0 bridge=xenbr0
"$dir/network-bridge" "$@" vifnum=2 netdev=eth2 bridge=xenbr2

[root@xenmaster003 xen]# ls -lah /etc/xen/scripts/an-network-script
-rwxr-xr-x 1 root root 281 Apr 15 09:56 /etc/xen/scripts/an-network-script

[root@xenmaster003 xen]# cat /etc/xen/xend-config.sxp | grep an-net -A 2 -B 2
#
#(network-script network-bridge)
(network-script an-network-script)