dynamically set up ipv6 for a 2-router dmz with openwrt

6cfg.daemon

#!/bin/sh

export PATH=/bin:/sbin:/usr/bin:/usr/sbin

radvdump | awk '/Router Advertisement/{router=$NF}; /interface eth0\.2/{good_if=1}; /interface br-lan/{good_if=0}; /prefix/{if(good_if && $1 == "prefix"){print router" "$2}}' | while read router prefix; do
	old_prefix=$(uci -q get "radvd.@prefix[0].prefix")
	new_prefix=$(echo $prefix | sed -e 's@1::1\?/64$@2::/64@g')
	lan_addr=$(echo $prefix | sed -e 's@1::1/64$@2::1/64@g')
	new_addr=$(echo $prefix | sed -e 's@1::1/64$@1::2/64@g')
	
	if [ "$old_prefix" != "$new_prefix" ]; then
		logger -t '6cfg' "Prefix changed from $old_prefix to $new_prefix, updating"
		uci set "radvd.@prefix[0].prefix"="$new_prefix"
		uci commit
		#ip -6 ro add $prefix dev eth0.2
		ip -6 ad sh | awk '/^[0-9]+:/{intf=gensub("(@.*)?:$", "", "g", $2)}; /inet6 2002:/{ system("ip -6 ad del "$2" dev "intf) }'
		ip -6 ro flush dev eth0.2
		ip -6 ad add $new_addr dev eth0.2
		ip -6 ad add $lan_addr dev br-lan
		ip -6 ro add 2000::/3 via $router dev eth0.2
		/etc/init.d/radvd restart
	fi
done

6cfg.init

#!/bin/sh /etc/rc.common

START=55

start() {
	uci set radvd.@prefix[0].prefix=''
	pgrep -f /usr/bin/6cfg >/dev/null || /usr/bin/6cfg &
}

stop() {
	killall 6cfg
	killall radvdump
}

readme.mkd

This allows using openwrt to dynamically set up an ipv6 network that looks like like

internet--<router1>--dmz--<router2>--internal 

I is useful for, say, 6to4 and DHCP-provided IP from the ISP; in order for routing to work scripts on the Internet facing openwrt must be modified to add an explicit route to the internal network.