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I have a desktop using two NIC's, I am trying to use one NIC for WOL as the other does not support it. I have everything configured and I am able to wake up the PC using the WOL utility from the router UI. If I try to use any tools installed on another computer on the same network or my mobile device, I am unable to wake the desktop. I used wireshark and can see the wol packet comming in when using the router UI but I dont see anything come in when using any other tools.

I access the UI from my laptop, which works, and on the same laptop I have tried installing a WOL utility but this does not work. The issue seems to be that the router is not broadcasting/sending the wol packet when the request was sent from outside the router.

Has anyone seen this behavior before or have any ideas? Do I need to do any extra configuration on my router for this scenario to work?

Thanks!

Schwagmister
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1 Answers1

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WoL uses a specially crafted pattern anywhere in a network frame. A packet may be routed, but not without special preparations.

Most tools use IPv4 and send a limited broadcast (to 255.255.255.255). L2 broadcasting (to ff-ff-ff-ff-ff-ff) won't work across a router generally.

Directed broadcast forwarding

You could use a directed broadcast (e.g. 192.168.0.255 for the 192.16.0.0/24 subnet) but the router needs to be specifically set up to forward that (ie. by default, it won't forward directed broadcasts). Depending on the routers and intermediate devices, directed broadcast forwarding isn't always possible.

Dummy ARP

Another method is a dummy IP address in the destination subnet. For the last-hop router to actually broadcast the packet, you set up a static ARP entry for that IP address with the ff-ff-ff-ff-ff-ff MAC address.

If the router doesn't accept the MAC broadcast you could effectively use any MAC address you don't use on the network, so the switch(es) would flood it as unknown. To be clean, you should use a locally administered address (LAA) with the second lowest bit in the first octet set to 1.

Without the static ARP entry, the router would try to ARP the IP address which would fail, obviously.

This method requires just a single IP address, regardless of which or how many nodes you want to wake up.

Zac67
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  • Thanks Zac67, do you have any resources for how I would configure the router to do a directed broadcast and the second option you mentioned with a static ARP entry? If possible, specific to the Asus GT-AC5300? So the issue here is that the tools I am using are sending a limited broadcast on the network where as the router is sending a full broadcast? Do you have any more details or resources on this behavior? Let's say I wanted to use wol both inside and outside my network using other clients (desktops, phone app, etc), what would be the best approach in this scenario? – Schwagmister Nov 01 '20 at 08:33
  • Sorry, consumer-grade devices are explicitly off-topic here, see the [help]. You might want to ask on [su]. We can't say what your tools do, usually they can be configured. If possible I'd use directed broadcast forwarding, otherwise dummy ARP. For a start, you might want to read [WP:Wake-on-LAN](https://en.wikipedia.org/wiki/Wake-on-LAN). – Zac67 Nov 01 '20 at 08:42