I have been having trouble re-establishing my 6-in-4 tunnel with tunnelbroker.net (Hurricane Electric) when my external IPv4 address changes. (CeroWrt 3.10.50-1 on WNDR3800)

I rummaged around the OpenWrt forums, found this hint at https://forum.openwrt.org/viewtopic.php?pid=255401#p255401 . According to the post, the problem is that the script to update the tunnel info runs immediately after the ppp link comes up, but that's before dnsmasq and other things are running. 

As suggested in the post, I added a "sleep 10" before the loop that retrieves the URL with wget in /lib/netifd/proto/6in4.sh

		... 
		# Add in sleep 10 
                # See https://forum.openwrt.org/viewtopic.php?pid=255401#p255401
                sleep 10
                while [ $((++try)) -le $max ]; do
			( exec wget -qO/dev/null "$url" 2>/dev/null ) &
			local pid=$!
			( sleep 5; kill $pid 2>/dev/null ) &
			wait $pid && break
		done
		...

This seems to have solved the problem: my IPv6 link has come back automatically three times since I edited the file.

Rich