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I'm trying to setup Wake-on-Lan for some of the LAN computers at home and it seems that I need to open a UDP port (7 or 9 being the most common) and forward all requests to the broadcast IP, which in my case is 192.168.1.255.

The problem is that my router does not allow me to forward anything to the broadcast IP.

I can connect to my router through telnet and it seems this router uses IPTABLES, but I don't know much about it or how to is.

Can someone help me out with the proper iptables commands to do what I want? Also, in case it doesn't work, the commands to put everything back would be nice too.

One last thing, rebooting the router will keep those manually added iptables entries or I would need to run them every time?

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  • A very similar question about Wake-on-Lan was asked fairly recently: How to get Wake-on-LAN working? The questioner's circumstances seem to be similar to yours, so the discussion there should be useful.
    – Steven Monday
    Nov 7, 2010 at 1:07

4 Answers 4

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# iptables -A PREROUTING -t nat -p udp --dport 6  -d <original destination> -j DNAT --to-destination 192.168.1.255

That will take a WOL packet destined for and reroute it to the broadcast of your network.

Also if you are using a Red Hat derived system you will need to save the iptables entry using 

# service iptables save
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  • When I do that iptables command and then try to list all rules with `iptables --list", that doesn't appear.
    – rfgamaral
    May 8, 2011 at 12:55
  • NAT rules are in the mangle table # iptables -t mangle -nL
    – Red Tux
    May 8, 2011 at 15:40
  • why --dport 6 rather then 9 (or 7) as sepcified in the question?
    – user83664
    Apr 3, 2015 at 16:55
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There's a great solution using the tool socat, mentionned on this StackExchange topic:

Transform a UDP unicast packet into a broadcast?

I'm not an expert at all on this topic, so I can't elaborate, I can only quote. This solution worked great for me.

The solution mentioned by Red Tux (https://serverfault.com/a/267343/323199) doesn't work, iptables is not made to broadcast a packet. This is explained in the StackExchange topic I mentioned above.

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Some routers (cisco) are able to forward directed UDP broadcast.

Linux kernel since circa version 5.0 is able to do this. You just need to specify a parameter for particular network interface:

sudo sysctl -w net.ipv4.conf.eth1.bc_forwarding=1

(Note: it seems the option net.ipv4.conf.all.bc_forwarding doesn't work)

You may save this parameter int /etc/sysctl.conf

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Add something like this:

iptables -A IN_FILTER -p udp -d 10.11.11.255 -j ACCEPT -m comment --comment "Depicus WoL"

http://linux.die.net/man/8/iptables will give you the syntax

Should survive a reboot but you never can tell until you try it.

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  • Shouldn't the port be specified too?
    – rfgamaral
    Nov 6, 2010 at 23:54
  • Sorry was late at night. Yes -dport 7 and -sport 7 to set the destination port and source port.
    – Depicus
    Nov 7, 2010 at 12:39
  • Your -A might not be IN_FILTER so do a iptables -L to get a list of rules.
    – Depicus
    Nov 8, 2010 at 13:52
  • There's a bunch of them, how do I know which one should I use? I saw in the documentation that -A is for append, what if I used -I to insert a rule for IN_FILTER? Not the same?
    – rfgamaral
    Nov 8, 2010 at 19:53
  • No you cannot add your own, the router would not know where to get them from. Best bet is to add a firewall rule similar to what you want in the web interface, just make it up. Then you can telnet in and see what section the new rule is in.
    – Depicus
    Nov 8, 2010 at 20:50

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