Wake On LAN / WAN over different Subnets OpenWRT (or other Routers)
you might have found several Tutorials about how to configure Wake On WAN or WAN.
Unfortunatly most of them lack of a good description how to get it work over a router.
In my case I’m using a OpenWRT Router which I want to use to Wake my LAN PCs from the WAN side of my Network. Well after this tutorial you should be able to achieve this goal with any router ;)
First of all, there are some Tutorials out there who consider to use a special unused IP Address and some static changes in your ARP-Table. I wouldn’t consider this as an clean solution, messing around with ARP-Entries seems more like a fast hack. So this is the more clean and easy way.
Okay let’s start.
Wake On … uses magic packages which are UDP-Broadcast-Packages send on port 7 or port 9.
Unfortunatly for our case, Broadcast UDP Packages won’t get routed into other Networks. This is way we can’t wake up PCs from different Networks by default and without using a proxy or remote agent inside of these networks.
But there is hope, for many Linux/Unix and Router Distrubutions you’ll be able to find the program udp-broadcast-relay which simply listens to a specified port on a specified interface and forwards all incoming UPD-broadcast-Packages to a different interface.
Keep in mind that this may need a firewall rule to allow traffic for the incoming or outcoming interface , port and protocol.
let’s say you want to send magic packages from the WAN Network of you OpenWRT Router into your LAN. It works by default the other way around to, so you’ll be able to Wake Computers in your WAN Network to - unless you block it with the OpenWRT Firewall
udp-broadcast-relay -f 1 7 eth0.2 br-lan
Explanation: udp-broadcast-relay the name of the program -f run as daemon (fork to background) 1 a unique id of the relay (I allways count this up for every relay) 7 the port to listen to eth0.2 the WAN Interface br-lan the LAN Interface
For OpenWRT you could just add two lines (for each port one line 7 & 9) to your startup script (/etc/rc.local or System/Startup) like this:
udp-broadcast-relay -f 1 7 ethX ethY
udp-broadcast-relay -f 2 9 ethX ethY
If one of these interfaces is firewalled like the WAN interface is, you need a Accept rule for the two ports (Network/Firewall/Traffic Rules/Open ports on router):
ACCEPT UDP Traffic (on Interface WAN) on PORT 7
ACCEPT UDP Traffic (on Interface WAN) on PORT 9
I hope you found this helpful