Configuring port mapping for wake-on-LAN

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Level 1

125 points

Configuring port mapping for wake-on-LAN

I had this working once upon a time, several OS's ago and with Airport Extreme base station. Now I have a Time Capsule and 10.5.4.

My Wake On LAN script (which is being run at a remote site) sends a magic packet to UDP port 9 of my public IP address. My LAN uses addresses from the 192.168.1.* range. I added a port-mapping entry to Time Capsule as follows:

Public UDP port: 9
Private IP address: 192.168.1.255 (i.e. the broadcast address)
Private UDP port: 9

(The targeted machine is attached to Time Capsule via ethernet.)

The packet never seems to get onto the LAN. I've confirmed this by running tcpdump on the LAN: I do not see any packets from the remote IP address.

Of course, I don't know for a fact that the packet is successfully arriving at my cable modem. That will be harder to verify, but I wondered if anyone knew of something obvious I'm doing wrong at my end. Do UDP port 9 ("discard") packets maybe get discarded somewhere along the way?

Thanks,
Chap

2.4GHz MacBook Pro, Mac OS X (10.5), Time Capsule 500GB

Posted on Aug 25, 2008 1:53 PM

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Answer 1

Sep 23, 2008 9:14 AM in response to Chap Harrison

Ever get an answer to this? I don't yet have an Airport Extreme or Timecapsule (am thinking of getting one of the two) but I have tried for hours and hours to get this working with other routers and came to agree with the posts I read that say most home-use routers will not let you forward to the broadcast IP address. I know there are a few routers (Ex. Linksys WRT54G - don't have it but read this) can do this, and, even though the Javascript in the web interface was trying not to let me, I was able to get this working on my Linksys BEFSR41 using a little hack to bypass the Javascript message. But anyway I've only found information that says that the Airport Extreme is one of the routers that can not do this, so if you can get it working I am interested to know. (I thought the Time Capsule was basically an Airport Extreme with an internal hard drive, but maybe not?)

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Answer 2

paddad21

Level 1

0 points

Oct 11, 2008 10:52 AM in response to everkleer

The time capsule does not allow port forwarding to the broadcast ip address. The time capsule will drop the packet.

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Answer 3

Oct 22, 2008 7:33 PM in response to Chap Harrison

I tried mapping the port to the address of my ethernet adapter:

Public UDP port: 9
Private IP address: 192.168.1.2
Private UDP port: 9

That didn't work either. Is there any way to wake a Mac remotely through Time Capsule? I've searched extensively and found nothing. Really disappointing since two out of three things I've wanted to do remotely through the Time Capsule haven't worked (Wake on lan, sharing of disk with remote Windows machines, and VNC access; only VNC seems to work). Thanks in advance for any assistance!

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Answer 4

Chap Harrison Author

Level 1

125 points

Nov 25, 2008 8:07 PM in response to everkleer

Sorry for late reply -- apparently the discussion board is not emailing me when replies are posted, despite my settings.

Short answer: no progress.

I was able to accomplish this with Airport Extreme, although they didn't want it to be easy: the GUI specifically disallowed typing '255' as the fourth octet of the private IP address. However, by Exporting to a text file, manually editing it, and re-Importing it, I could get AE to forward to the broadcast address.

TC allows you to enter 255 in the GUI, but apparently ignores it!

Rot.

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Answer 5

Dec 6, 2008 8:42 AM in response to Chap Harrison

The key to success here is to setup the subnet mask on your router to 255.255.255.128.
Then forward UDP port 9 to 192.168.0.127 (or whatever for the first three octets) - which is the broadcast address for that subnet.
Many (if not all) routers will not allow port forwarding to the broadcast address .255 on a /24 network

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Answer 6

Camelot

Level 9

54,333 points

Dec 6, 2008 11:19 AM in response to kludgeless

I tried mapping the port to the address of my ethernet adapter:

That would never work anyway - when the machine is asleep it does not have an IP address. Wake-on-LAN specifically targets the broadcast address just for that reason.

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Answer 7

Chap Harrison Author

Level 1

125 points

Dec 6, 2008 2:59 PM in response to googleplex3000

Is there a way to set the subnet mask on the Time Capsule? Using Airport Utility, going to Internet > DHCP, I can select among three local network prefixes (192.168, 172.16, and 10.0) but I can see no way to specify the subnet mask.

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Answer 8

Dec 9, 2008 3:24 AM in response to Camelot

Just to stifle further experimentation:
- No, binding the IP address to a MAC in the Airport BS doesn't solve this
- No, increasing the DHCP lease timeout doesn't solve this, either

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Answer 9

Tim Haigh

Level 7

24,198 points

Dec 13, 2008 10:09 AM in response to Chap Harrison

Apple's base stations and time capsules are great routers but lack features that other routers boast. They do however make fantastic access points and are easy to setup.

You could get a router such as a linksys wrt54g and install openwrt or dd-wrt firmware on it. This firmware allows you to install a wake on lan client inside the router. You could then ssh into the router from anywhere and send the magic packet from the router to the MAC address of any computer on that LAN.

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Answer 10

tompijls

Level 1

0 points

Dec 22, 2008 11:31 AM in response to Chap Harrison

hi chap, what version are you using? My airport extreme (firmware 7.3.2 with airport utility 5.3.2) allows to add 255 as last octet, but it has no effect.

Best,

Tom

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Answer 11

tompijls

Level 1

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Dec 22, 2008 11:32 AM in response to googleplex3000

hi googleplex, could you explain how you managed to change subnet?

Best,

Tom

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Answer 12

Chap Harrison Author

Level 1

125 points

Dec 22, 2008 9:43 PM in response to tompijls

Tom,
My Time Capsule firmware is at 7.3.2, and I'm using Airport Utility 5.3.2. Like you, I can add 255 as the final octet in Port Mapping, but it has no effect: using tcpdump, I don't see anything appear on the local area network when I send the appropriate packet from an external host to my public IP address.

I don't know the firmware level, or the Airport Utility version, when I had the Airport Extreme.

Chap

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Answer 13

tompijls

Level 1

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Dec 23, 2008 11:00 AM in response to googleplex3000

This does actually work for me.

First i made sure that all NAT port mappings and DHCP reservations were below x.x.x.127

Then i saved from airport utility the configuration to a file.

With a text editor , I replaced all occurrences of 255.255.255.0 in this file to 255.255.255.128.

Load the configuration file back in the airport utility and update the airport extreme.

Create a Nat port mapping to port 9 on the pc to wake up

Now send the magic packet to the external ip/port boots the pc

not sure if this is a supported way of working so do it at your own risk

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Answer 14

Chap Harrison Author

Level 1

125 points

Dec 23, 2008 6:30 PM in response to tompijls

In your procedure you said:

tompijls wrote:

Create a Nat port mapping to port 9 on the pc to wake up

Is that what you did, or did you create a NAT port mapping to port 9 +of the local broadcast IP address?+

I would have thought that you would map your WAN IP address + port 9 to your LAN broadcast IP address + port 9 (e.g. 192.168.1.127).

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Answer 15

tompijls

Level 1

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Dec 26, 2008 1:39 AM in response to Chap Harrison

seems i was over enthusiastic. I did map to ip local pc, but the wakeup over wan only works for a brief period of time. this will probably also work if you leave the default subnet mask.

mapping to .127 local broadcast address has no effect

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