core-admin/proxyvm/bin/qubes_netwatcher

#!/bin/bash
set -e

PIDFILE=/var/run/qubes/qubes_netwatcher.pid
CURR_NETCFG=""

# PIDfile handling
[[ -e $PIDFILE ]] && kill -s 0 $(<$PIDFILE) 2>/dev/null && exit 0
echo $$ >$PIDFILE

trap 'exit 0' SIGTERM

while true; do
	NET_DOMID=$(/usr/bin/xenstore-read qubes_netvm_domid)
	if [[ -n "$NET_DOMID" ]] && [[ $NET_DOMID -gt 0 ]]; then
		NETCFG=$(/usr/bin/xenstore-read /local/domain/$NET_DOMID/qubes_netvm_external_ip)
		if [[ "$NETCFG" != "$CURR_NETCFG" ]]; then
			/sbin/service qubes_firewall stop
			/sbin/service qubes_firewall start
			CURR_NETCFG="$NETCFG"
			/usr/bin/xenstore-write qubes_netvm_external_ip "$CURR_NETCFG"
		fi

		/usr/bin/xenstore-watch /local/domain/$NET_DOMID/qubes_netvm_external_ip
	else
		/usr/bin/xenstore-watch qubes_netvm_domid
	fi
done