How to wake on Lan in order to wake up my computer

I'm trying to send a Wake on Lan in order to wake up my computer. From within my own network, I'm able to wake it up without conditions. However, if I try to wake it up from outside my network, it doesn't work.

It's an odd behavior because if I send the WOL a few seconds after the computer has shut down (less than 30 sec) it wakes up from the internet but if I try it after one minute it doesn't wake up.

I have a Movistar Homestation router if it helps and I'm sending the magic packet through port 9 (which is redirected to my computer private IP)

Thank you

Solution

I assume you have mapped your pc's mac to the IP you are sending the WOL. Have you created an entry in the ARP table of the router? The router could be cleaning the table after a few time and, when the WOL arrives to the computer, it doesn't know which MAC is for that IP.

If it doesn't work anyway, could you do some tests?

Change the port to port 7
Change the IP to the broadcast IP
I've read you could telnet that router and then you could add a permanent ARP entry in case your router's console doesn't let you(I can't test it)