Wake on Lan through router to repeater client to router from outside LAN

Question

Let's say I have an Internet connection with a public IP address 123.123.123.123. This connection is going to a router which gives out addresses from 192.168.1.100 to 192.168.1.200.

A repeater is connected to the router as a client. The repeater is then connected to another router, which gives out addresses from 192.168.2.100 to 192.168.2.200.

The IP of the computer I want to wake up, which is on the second router, is 192.168.2.102, and the MAC is 11:aa:11:aa:11:aa.

Wake on LAN works using 192.168.2.102 on local network using MAC 11:aa:11:aa:11:aa.

How do I make Wake on LAN work from an outside IP with this setup?

Here's a chart to illustrate the setup:

                      Router with                                    Further router with 
                      built-in                                       built-in DHCP. 
                      DHCP server                     WAN port---|   192.168.2.100-200 range                         [Target Computer]
                      |         |                                 \->|             |                                  |
                      |         |  LAN with range 192.168.1.100-200  |             |                                  | 
External IP   --------/          \-------------------(repeater)-----/               \----------- (LAN part 2) ---------
123.123.123.123                    WOL does not work for target                               WOL works for target        

Answer 1

To be able to do this your inner router must support Subnet Directed Broadcasts.

Subnet directed broadcasts

A principal limitation of standard broadcast Wake-On-LAN is that broadcast packets are generally not routed. This prevents the technique being used in larger networks or over the internet. Subnet Directed Broadcasts (SDB) may be used to overcome this limitation. SDB may require changes to intermediate router configuration. Subnet directed broadcasts are treated as normal network packets until processed by the final (local) router. This router converts the packet into a true broadcast packet. This technique allows a broadcast to be initiated on a remote network but requires all intervening routers to forward the SDB. When preparing a network to forward SDB packets, care must be taken to filter such that only desired (e.g. WoL) SDB packets are permitted—otherwise the network becomes a participant in DDoS attacks such as the Smurf Attack.

Refer to your router's firmware documentation to see if it supports this feature.

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Your 2nd option is have a computer that is always on in the inner LAN listening for a normal TCP connection and have that computer broadcast the WOL packet (If you have a customizeable firmware like dd-wrt you could have the router itself be that computer). This is what the service LogMeIn does to do it's WOL, if it detects that two computers on the same network are using the service it will use the on computer to broadcast a WOL packet to the off computer.