Cable Modem How To


This is a brief howto based on a single experience of setting up a wireless cable modem router using the NTL cable broadband service. Feel free to update this document with your own experiences. It is intended as a guide to augment the documentation provided with the equipment and hopefully make things a little easier.

Although this is specific to one situation, other system setups are likely to follow similar principles.

Please also bear in mind that these notes were made from memory shortly afterwards, and that the installation didn't necessarily follow the precise steps noted here. These steps are those that based on hind-sight and experience are likely to work reasonably well.


All information herein is presented "as-is", with no warranties of any kind, expressed nor implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose. Use the concepts, example and information at your own risk. The author(s) do not take any responsibility for damages that may arise from the use of this document.

Under no circumstances will the author(s) of this document be liable for any damages whatsoever arising out of the use of this information. If you damage your equipment or breach any conditions imposed by suppliers, this is entirely at your own risk. There is no guarantee whatsoever that any of this information is in any way correct, nor suited for any use whatsoever.


As of the time of writing, NTL do not support more than one computer being connected to their network. However, it is possible to connect via a single modem router, such that it, to all intents and purposes, appears to be a single computer connected to the Internet.

In brief, when setup correctly, your wireless router will act as a gateway to the Internet, with all traffic directed to and from the Internet, passing through the router.

Each network card has a unique MAC address, normally permanently set during manufacture. This includes the wireless adapter attached to your PC and also the router.

Where a provider constrains your access to their systems to a single machine, it is highly likely this is done by only accepting connections from a computer with a specific MAC address. To cope with this situation, it is common that the MAC address of cable (and ADSL) modem routers can be changed. Make sure the router you purchase provides the facility to change its MAC address.

It appears, that during the registration process, the software picks up the MAC address of the machine that the registration software is running on and registers this as the single machine that can connect to the NTL network. It is therefore necessary to change the MAC address on the router to match that of the computer used during installation.

Equipment Used

  • NTL Cable set-top box
  • Sitecom Wireless Network USB Adapter
  • Sitecom Wireless Network Broadband Router
  • Desktop PC running XP Home edition

Note: The availability of a machine with a built in network card that can be directly connected to one of the PC ports on the router, is desirable. There are options you can change on the router that may stop you being able to communicate with the router via the wireless connection, making it difficult to correct the configuration. Of course, you should be able to start again by resetting the router.


  1. Ethernet CAT 5 cable between set-top box and Router. Note: Depending on the model of the set-top box, this may be a cross-over cable or not. NTL should supply both. The back of the set-top box indicates whether cross-over. This connects with the socket marked WAN (Wide Are Network) on the router.
  2. USB connection between wireless USB adapter and Desktop


Wireless Network

It is best to ensure your wireless network is working correctly before connecting to the cable modem. This eradicates a set of possible failure points before starting to connect to NTL and the Internet.

At first, it is easiest to set up the wireless Local Area Network (LAN) with the minimum of features enabled, as again, this reduces complexity and the potential number of possible failure scenarios. However, this does mean that it is totally insecure. You must evaluate the risks, likelihood and consequences of someone being able to access your systems during this period.

If you have important data that may be exposed, you should make your wireless network secure before connecting to the Internet. In principle this involves techniques such as setting up a firewall, implementing WEP encryption and limiting access to machines by their MAC address. This is not covered in this document.


Follow the instructions for setting up the router. This amounts to little more than powering it on. It shouldn't be connected to the set-top box at this time.

Wireless Adapter

Follow the instructions for setting up the adapter. These vary for the operating system you are running. Be careful to note whether you should install the software before or after plugging the adapter into the machine.

Windows often recognises new hardware plugged into the machine and will set it up with the best drivers it has to hand. If you haven't already installed the drivers supplied with the adapter, it may not work well if Windows picks an alternate driver. If this happens, you can manually install the correct drivers, but it's not absolutely straight-forward. It's much easier to follow the instructions carefully, first time!

Once the adapter is working correctly you should have a new icon in the task bar, representing the adapter. There may also be a 'generic' windows network icon. Identify the adapter icon and use your mouse (by right or left-clicking) to select 'properties'. This should produce a multi-tabbed dialog.

You may need to use this dialog to browse for Access Points (AP) and select the option to connect to it. Refer to the instructions for this procedure.

Testing the network

Two options for testing the network are listed here.

Testing the Router Connection with a Browser
  • Most routers have a little on-board web-server that allows you to change its configuration settings. The Sitecom router's configuration is accessed by entering the following URL in a web-browser (such as Internet Explorer). '' (without the quotes.) Note the forward slashes not back-slashes ('\'). Again, if this web page is displayed, we have a good connection.
Pinging the Router
  • Open a command shell by selecting 'Run' from the start menu and entering either 'cmd' or 'command' and clicking OK. (One of these commands will work, depending which version of Windows you are running).
  • At the command prompt, Enter the command 'ipconfig /all' (without the quotes) and press return. You will see a listing similar to the following:

Windows IP Configuration

          Host Name . . . . . . . . . . . . : MYHOSTNAME
          Primary Dns Suffix  . . . . . . . :
          Node Type . . . . . . . . . . . . : Hybrid
          IP Routing Enabled. . . . . . . . : No
          WINS Proxy Enabled. . . . . . . . : No

Ethernet adapter Local Area Connection:

          Connection-specific DNS Suffix  . : 
          Description . . . . . . . . . . . : My Ethernet Card
          Physical Address. . . . . . . . . : 99-99-99-99-99-99
          Dhcp Enabled. . . . . . . . . . . : Yes
          Autoconfiguration Enabled . . . . : Yes
          Autoconfiguration IP Address. . . :
          Subnet Mask . . . . . . . . . . . :
          Default Gateway . . . . . . . . . :
          DHCP Class ID . . . . . . . . . . : ???
  • There should be an IP address listed as the default gateway, and is likely to be similar to '' however it will differ according to the preferences of the router manufacturer. If no IP address is specified, we haven't got a successful connection to the router. Re-check the instructions, especially how to setup your Windows network connection.

  • If an IP address is shown, we should be able to do a small test called 'ping' to see if it responds. At the command prompt enter 'ping' (or whatever is the IP address of the gateway). If everything is working well, you should see the following output:

    Pinging with 32 bytes of data:

    Reply from bytes=32 time=1ms TTL=64 Reply from bytes=32 time<1ms TTL=64 Reply from bytes=32 time<1ms TTL=64 Reply from bytes=32 time<1ms TTL=64

    Ping statistics for Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 0ms, Maximum = 1ms, Average = 0ms

  • If it fails, you'll see output similar to the following:

    Pinging with 32 bytes of data:

    Request timed out. Request timed out. Request timed out. Request timed out.

    Ping statistics for Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

Note: This can also fail if the firewall has been enabled on the router and set not to respond to ICMP packets. If you've already set up the firewall, you may like to temporarily disable this feature to perform this test.

Re-establishing Connection
  • At this stage, it is a good idea to sort out re-establishing the connection after rebooting your PC. You ought to be able to set it up to automatically establish the connection. Refer to the instructions. With the Sitecom router, we had to create a profile setting.

  • Once you're confident you can reliably establish a connection after a reboot, you can move onto Connecting to the Internet Service Provider (ISP).

Connecting to the Internet Service Provider (ISP)

Bear in mind, the instructions provided by your ISP (in this case, NTL) are likely to be intended to connect a single PC to the set-top box or cable modem and you need to answer questions during the installation procedure accordingly. E.g. We were connecting the PC to a USB wireless adapter, but the Wireless router was connected to the set-top box by an Ethernet cable. When asked whether the connection from our PC to the set-top box was USB or Ethernet, we responded 'Ethernet' as the connection into the set-top box was Ethernet. The USB adapter connection was irrelevant.

We originally registered the computer leaving the router's MAC address at its default setting. We then rebooted and failed to connect to the Internet. We then changed the MAC address of the router to that of the PC. With hind-sight, I would change the MAC address of the router before attempting to do the registration.

Changing the Router's MAC Address

  • Find your PC's MAC address using the command 'ipconfig /all' in a command shell. This should be the MAC address of the PC you are going to use to register the connection to the ISP.
  • The 'ipconfig /all' listing shows the MAC address against 'Physical Address' in the form of 99-99-99-99-99-99
  • Connect to the router's configuration web page as described here.
  • Find the page where you can change the MAC address of the router and enter the MAC address of your PC.
  • Save the changes. Some routers require a 'reboot' after changing the settings. The Sitecom didn't require a reboot.
  • You are now ready to register the connection with the service provider.


  • Carefully follow the instructions provided for the registration process, bearing in mind they are written with the expectation that you are connecting a single computer directly to the set-top box or cable modem.
  • When you get to the section where it asks if you want to install various pieces of software, you can probably skip this. Personally, I am very reluctant to install software, unless I'm fairly sure I need it. Your call!
  • I believe at this stage, the registration process will have recorded the MAC address of the PC used to do the installation, and will only allow a computer or router with that MAC address to connect to the Internet. If an unregistered MAC address is used, the IP traffic is redirected to the registration servers, forcing you through the registration process again.
  • Keep a note of the MAC address that will have been registered, as it may come in useful if you replace the router. Alternatively, simply inform the ISP that you have changed 'computers' and no doubt you can run through the process again. With NTL, I suspect you can simply re-run the registration process again.


The following links may offer some further help:

-- Frank Dean - 29 Feb 2004

Related Topics: LinuxHintsAndTips, WindowsXP