[Gllug] Setting up ntl cable modem/DHCP?

Robert McKay robert at mckay.com
Sun Apr 21 17:36:04 UTC 2002

On Sun, 21 Apr 2002, Kim Hawtin wrote:

> > I think I could be tantalisingly close to getting a cable modem up and
> > running with my Debian box (Woody on a Compaq Professional Workstation
> > 5000 PPro SMP) if I could just get my DHCP client to talk to my cable
> > operator's DHCP server.

> ok, im using a cable modem attaached to my debian box, and i use
> pump (dhcp client) to get the lease. but i have to spoof the
> hardware address of the network card that is in my laptop, because
> that was the first machine to be setup using it.

The NTL dhcp servers will serve an IP to any MAC address, however; the
cable modems are configured via their tftp'd configuration files to only
accept one MAC address at a time. The MaxCPE setting in the docsis config
is what does this. The cable modem just locks onto the first MAC address
it sees. In order to switch ethernet cards, simply reboot your cable
modem; the old MAC will be lost and it'll lock onto your new ethernet

You can find out more than you ever wanted to know about NTL here.. it's a
very interesting site:


also check out

http://docsis.sourceforge.net for tools that will allow you to decode the
cable modem configuration files... which is quite fun. =)


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