How To: Wake on LAN / Wake on WAN

[thiggins]

Waking your PC up over the Internet can come in handy. Doug Reid shows you how.

[ratchet]

Having read Doug Reid's comprehensive article on WOL, I've just spent the week trying to get my desktop powered remotely. From with in the LAN I am able to do it, however, when I tried it over the internet it has always been a complete failure. I "slowly" re-read the article today and I believe I discovered the problem. I have been trying to send the magic packet via a notebook connected wirelessly to the internet. I was under the impression that only the host, desktop needed to be hard wired, failing to pay attention to "both the PC to be turned on and the PC sending the WOL signal need to use wired Ethernet connections". Is this indeed the problem and is there any work around? Thank You!

[jdabbs]

What's the transmission path of the magic packet?

Is it wireless notebook>Internet>home router>desktop, or wireless notebook connected to remote device (router/other PC on network) initiates sent packet to desktop?

If the former, it will likely fail as magic packets only work on the same broadcast domain.

I managed to do it.

- set the router to give a fix IP via DHCP to the computer you want to wake up
- set port forwarding on the router to the above fix IP
- send the magic packet via internet (I used HSDPA mobile net) but be careful to set the subnet mask to 255.255.255.255

I think that's all.

Hi,

I read the WakeOnLan guide trying to troubleshoot a problem (http://www.smallnetbuilder.com/conte.../29941/53/1/5/), which led me here. Basically, I set up WakeOnLan on my desktop and tested it. It works fine at first, I've verified that magic packets are being received.

But then, after about 30 minutes or so, the desktop stops responding to magic packets! I know that IP addresses are lost after a certain amount of time, so I tried sending to the broadcast IP, but it still does not work. What am I missing here?

Thanks for any help,
Mike

Verry nice tutorial. thx!

Originally Posted by Mike

Hi,

I read the WakeOnLan guide trying to troubleshoot a problem (http://www.smallnetbuilder.com/conte.../29941/53/1/5/), which led me here. Basically, I set up WakeOnLan on my desktop and tested it. It works fine at first, I've verified that magic packets are being received.

But then, after about 30 minutes or so, the desktop stops responding to magic packets! I know that IP addresses are lost after a certain amount of time, so I tried sending to the broadcast IP, but it still does not work. What am I missing here?

Thanks for any help,
Mike

This is caused by two different things.

First - you are partially correct in saying that ip addresses are lost after a certain amount of time - a more accurate way to put this is that the "ip address to MAC address" pairing is flushed from the arp cache.

ip addresses are not used for local (as in local area network) communications - the ip stack compares the destination ip address to the source ip address & subnet mask to determine if the destination and the source are on the same network, and if they are it will send the data directly to the destination using it's MAC address, if they are not, it will send the data to the router (as specified in the source hosts's routing table) using the router's MAC address, for onward routing.

Now - the MAC address of the destination host is unknown to the source so it uses a protocol called arp - address resolution protocol - to get it, and it stores that in the arp cache for an unspecified period of time - arp works like this - the PC that needs the address sends a broadcast asking "who has ip address a.b.c.d?" and the PC with that address answers.

I'm sure you see the problem here - after you switch off the computer - it cannot respond to the arp request - so after the router's arp cache is flushed the router does not know where to send the magic packet, does not get a response to an arp request, and then drops the packet.

This explains why it works when the computer is first switched off but after a few moments will stop working.

The fix is to send the magic packet to the LAN's broadcast address which SHOULD cause the router to broadcast it to all hosts using the broadcast MAC address - but - as you discovered this does not work either.

Most consumer routers do not allow "ip directed broadcast" which is what is required for you to send a broadcast packet from the WAN side to the LAN side - this is a security issue and a potential attack vector that can be used to hack systems on the inside of the LAN as well as to use those systems in denial of service attacks (smurf attacks) on other targets.

ARP cache - how to check it it is flushed or keeped ? I own a canyon Wf 514 router, wher the desktop is connected over wired lan. When I try wakeOnLanGUI in the lan, it works without any problems, but if I send this signal over wan it works only a couple of minutes after something is changed in the configuration of the router, after that - not. Please help me with this issue. Thank you in advance

I have understood that the arp cache is dynamic and is loosed after a couple of minutes. Is there a possibility to add static arp record in the router CN-WF514 ( canyon ) so I can send WOL request from WAN to this computer in the LAN?Thank you in advance

Assuming 192.168.1.1 is the address for your router,
Try this from command prompt: telnet 192.168.1.1
then: arp -s 192.168.1.64 00:00:00:00:00:00

In the above example, the ip address is the address of the PC you want to wake. And what follows is the MAC address. This worked for my Actiontec GT704WG. Basically, I did a search for ARP Actiontec. Good luck.

TC