xDSL Internet connection sharing

Want to share your xDSL Internet connection? Try out the following guide. Note that this guide comes without any guaranty of any sort, you’re on your own here.

If that’s fine with you, read on.

You’ll need three devices:

  1. xDSL modem;
  2. A (optionally wireless) router;
  3. One (or more) host machines.

Some of the newer xDSL modems have additional functionality, but we shall focus on making the modem act as a bridge, a so-called dumb device, between the Wide Area Network (WAN, or the Internet) and your Local Area Network (LAN), which is your router and host machine(s).

If you already have an existing xDSL service, you will already own a modem and host machine, so all you will need in addition is a router; I recommend the Linksys WRT54G (or WRT54C is OK too), which has served me (and my friends) faithfully.

Your xDSL modem has at least four ports (Power, USB, Telephone, Ethernet). We will focus on the Telephone and Ethernet ports. If your modem has more than one Ethernet port, it means that your modem is an all-in-one device with WAN/LAN functionality, so you won’t be needing to read any further!

So suppose we only have one host machine; the final setup should look like the following. where ‘—–‘ represents a Ethernet cable, which looks like a (fat) telephone cable.

xDSL modem [Ethernet port] —– [Internet port] Router [Ethernet port 1] —– [Ethernet port] Host machine

But first we need to set the modem to bridge mode. Connect as follows:

xDSL modem [Ethernet port] —– [Ethernet port] Host machine

Now you need to access the modem’s web interface (assuming it is a fairly modern device!). Make sure your Ethernet connection is set to ‘DHCP’, so that the host machine gets a local Internet Protocol (IP) address. I will be using the default 192.168.1.x convention. Now our machine has an IP address like 192.168.1.100 (or whatever, just as long as it is different from the modem). The gateway (modem) should be 192.168.1.1, and we can then access the web GUI using the browser like http://192.168.1.1/.

Each web interface differs, but you should be looking for ‘bridge’ mode. Set it to bridge mode, and disable DHCP. The modem will restart, and the machine will no longer have an IP address (because DHCP is disabled). Now we connect as follows:

Router [Ethernet port 1] —– [Ethernet port] Host machine

The router should be configured to PPPoE (xDSL) mode — you will be prompted for the username and password to the DSL service with your Internet Service Provider (ISP). Also set the router IP address like 192.168.1.2 and enable DHCP. Remember that the IP address must differ from the address of the modem; e.g.

xDSL modem [192.168.1.1]
Router [192.168.1.2]

You can ask the router to begin allocation host machine addresses from a certain number onwards; e.g. 10. So the first host machine would be:

Host machine [192.168.1.10]

Now let’s set everything to its final connection state:

xDSL modem [Ethernet port] —– [Internet port] Router [Ethernet port 1] —– [Ethernet port] Host machine

Note that you cannot access your modem’s web GUI anymore; instead access your router’s web GUI at http://192.168.1.2/. Let’s log in, and click the ‘Connect’ button (you’ll find it somewhere!). If everything works out, your router will receive a WAN IP address from the ISP, and you’re good to go!

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