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This is fairly straightforward, but appears to be subject to the fundamental limitation that the Fritz Box cannot make use of multiple external IP addresses for the port forwarding, even if you are on an 8 port subnet like I am. I made absolutely sure that the Fritz Box was aware of the subnet by accessing its menus, then navigating to Home Network/Network on the left menus, and then clicking on the Network Settings tab. You then click on Additional settings to reveal some extra settings, and then scroll down and then click on IPv4 settings. Finally, if you scroll down and look under Public IPv4 Subnet you will see the public subnet visible/allocated to the Fritz Box, as a prefix and network mask.

In my case this was clearly an 8 port subnet, but unfortunately the fritz box only allowed port forwarding using the primary router public IP address.

I managed to work within this limitation however, as you can still forward multiple different ports to multiple different local devices. For example, to enable inbound RDP access to a PC as I did, do the following:-

1/ Visit Internet/Permit Access on the menus, and then click the Add device for sharing button.

2/ Select the target PC/device at the top, then at the bottom click New Sharing, which configures the desired sharing for the device.

3/ Then Click the Port Sharing radio button (as opposed to the default My FRITZ! sharing). Under application, I selected MS remote Desktop as the Fritz box was aware of RDP. You can select Other Application and enter the ports manually if you are working with an application that the Fritz box is unaware of.

4/ You then have 3 ports to configure, which is slightly confusing – I was not clear on all of this and the online help was blank on some of this detail. When I selected MS Remote Desktop, Port to Device and through… were both set to 3389, which was the correct internal port to use for RDP. Below this was Port requested externally, which is the actual external port you want to use. In one case therefore I left the defaults, but for a second PC, I set the external port to 3390, which allowed me to use the same external IP address for 2 different RDP configuration to access 2 different internal PCs successfully. I was not clear however what the distinction between Port to Device and through… was all about, but did not need to touch it.

5/ When accessing via the MS android RDP app, I was able to configure multiple PCs as required, and could also configure both Lan and internet configurations of the same PC so that I could access it both ways from my phone. A key trick here is that this app does allow a different RDP port to be used. Under PC name for the internet, I set the target IP address (the public IP address of the router), and appended a different port using e.g. :3390 notation to use port 3390 instead of 3389. You are able to give an additional friendly name for the PC when doing this, which is useful when configuring external IP access. Internally on the lan you can just use the standard windows network names. This then all worked fine and I was able to use my phone both to remotely access the fritz box to wake the PC, and then remote login using the MS RDP app to access it.

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