I use a Speedtouch 716 v5 WL and it’s been a pretty decent ADSL modem. However one of the issues I had with this modem was it’s behaviour when referring to a domain name which would ultimately point towards and internal server using the modem’s NAT. This was impossible to do as the modem would point directly to the modem itself instead of to the device behind the modem. So today I finally got an insight and this seemed to work. I have written it down in the hope somebody else – or myself when I have forgotten all about this – might be able to replicate this solution.

This howto has been written and tested on a Mac with OS X and should also work with Linux. It has not been tested with Windows and I’m not able to test it myself on that operating system at the moment. Keep in mind that I’m by no means a network specialist nor claim to be. It worked for me, but I cannot guarantee that it will work for you. Hell, it might even make your modem useless. Use at your own risk!

Ingredients:

• A server called SERVER in your local network with the ip address 192.168.1.60
• The modem gateway with the ip address 192.168.1.254
• A domain name, e.g. example.com
• access to an external DNS server
• The command-line guide for the Speedtouch 716 v5 WL
• experience in using the commandline and some courage
• basic idea of what DNS means and does

Replace the ip addresses and names with your own.

Goal:

We would like to have SERVER using the following domain name: SERVER.example.com for both inside the local network as well as outside for the Internet.

Howto:

Before you do anything else, make very very sure you have made a backup of the working configuration! You can create a backup by logging into the modem, selecting ‘Configuration’ and then ‘Save/Restore configuration’. Now you should see something similar to this screenshot.

Press ‘Backup configuration now..’ and follow the instructions. Confirm that your backup works! In case something went wrong you’ll need to be able to restore it by using the same interface you just used to create a backup, but then you’ll have to select ‘Restore saved configuration’.
We continue with changing our outside DNS entry. This is necessary before we can access the device behind the modem from the Internet. Basically we want to point the domain name or part of the domain name towards the ip address in use by the modem. We do this by creating a zone called ‘server’ of the record type A with the ip address of the modem as target. Please refer to your specific DNS server for the details. Now we have created the subdomain intra and our modem should be reachable by entering in ‘server.example.com’ in your browser. At least after the changes have been propagated between all DNS servers which usually takes between 24 till 48 hours. In the mean time we need to make sure the modem is willing to accept traffic.

In order to let traffic pass the modem we need to determine which type of traffic we would like to let in. In this example we want only allow traffic for a http (aka web) server, secure http server (aka https) and ssh. For each of those we need to determine which device behind the modem is supposed to deal with it. In our case it will be one physical machine doing this which we already introduced as SERVER. Now select ‘Home Network’ and then ‘Devices’ within the modem webadministration interface. Pick the device associated with SERVER. The easiest way to do this is by checking the ip-address associated with the device. In this example this means the device with the ip-address 192.168.1.60. After selecting it we can change the name if necessary. In our case the device was called ‘Unknown-00-17-18-ef’ and so we changed it to SERVER by selecting ‘configure’ (upper-right corner) and gave it the name SERVER. You can also change the type, but it’s doesn’t seem necessary so we’ll leave that for now. Don’t forget to press apply after the changing the name.

Now we want to open the ports for the earlier mentioned services (http, https and ssh). This can be done by selecting the appropriate services beneath the ‘Connection Sharing’ title. If the predefined ones are not suitable, because you don’t want to use the standard external ssh port 22, but instead would like to use port 99999 for instance, you can add your own by going to the ‘Toolbox’ section and selecting the ‘Game and Application Sharing’ option and then the ‘Create a new game or application’. Follow the instructions and you should be fine.

Now, presume we its two days later. Check if you can reach SERVER from the outside by typing http://server.example.com in your browser. This checks if http works. Do the same for https and check ssh by entering ssh server.example.com in the terminal. This presumes that SERVER has already been configured with a http server, https server and a ssh server. It also presumes that the username for ssh is the same for the machine you’re connecting from as the one (SERVER) you want to connect to. If all went well, you should see the webpage set on SERVER or a request for a password when connecting with ssh.
Congratulations, the access to SERVER from the outside works.

If you tried to access SERVER by typing server.example.com from the inside you probably have failed in doing so. At least that’s what happened with me. I fixed this by connecting to the modem via the command-line (the things we’re about to do cannot be done using the web interface) using telnet. Start by opening a terminal and typing:

telnet 192.168.1.254

After this you should get a prompt asking you to type the username and after you’ve entered that, a password.

If you’re in the modem you need to type in:

dns server config domain example.com

This will set the domain for all the machines in the local netwerk to example.com. This means that we have achieved what we wanted, namely accessing SERVER by typing in server.example.com Due to the fact we gave it already the name SERVER in the web interface this works as expected.

Now there is a caveat: if you use the domain example.com also for other machines outside the internal network you will need to add these to the internal dns otherwise they won’t be resolved correctly. So if you use mail.example.com the internal DNS expects it to be one of the machines in the internal network. To change this you need to add the external hosts to the server with their external ip address. This will make the internal DNS work as expected again. To do this you have to use the modem command line and type:

server host add

Now the modem will prompt with:

name=

Type in the name of the host, in this case mail and press ENTER. The modem will prompt with:

[addr] =

Now type the external ip address of the server being used with the domain name mail.example.com

I hope this howto was useful for you and feel free to post any comments with your experiences.