[ale] Question about cable modem connections

Pat Regan thehead at patshead.com
Thu Oct 2 19:39:45 EDT 2008


Geoffrey wrote:
> Jim Kinney wrote:
>> All the cable modem crap I've dealt with require a registered MAC address.
>> So the installer sets up the box i.e. - plugs it in) and then phones in to
>> have the new device "approved" witht he MAC address of the WINDOWS PC
>> plugged into it. The modem does not provide dhcp. The upstream cable service
>> provides it.
> 
> This has not been my experience.  I've just recently replaced a single 
> pc connected to a Comcast modem with a wireless router.  All I had to do 
> was power everything down, power the Comcast modem up, then power the 
> router up.  The router provides dhcp to the rest of the computers in the 
> house.  In this case, they had two desktop computers connected via 
> ethernet to the router and one laptop that is connected wirelessly.

I think one of the problems with this discussion is that two different
things are being discussed.  The modems and the PCs.

I would imagine that every cable modem in the country is DOCSIS 2 by
now.  Since all the cable modems in a neighborhood share the same line
the cable company needs to associate the MAC of the cable modem with
you.  In theory you could probably take your activated cable modem and
plug it in anywhere in your neighborhood and it might work (assuming
they don't block that cable modem channel at the pole, I am ignorant of
that piece).

They actually use the MAC of the modem to upload your bandwidth limits
to the modem.  I remember people getting in trouble for tftp-ing new
rules to their modems to remove the bandwidth caps a bunch of years ago.

As for the modem locking in on a single PC MAC.  I don't think I've seen
a cable company actually lock you down "permanently" to a single MAC
since the pre-DOCSIS days.  Every modern cable modem I've seen will
associate with a fresh MAC every time it is powered down.

I can probably name a dozen cable companies in a half dozen states that
that has been true for.  I think they learned a long time ago that it is
a waste of tech support time to lock the PCs.  Or maybe they just had no
way to track by modem in the pre-DOCSIS days.

My first cable modem in the late 90s was hysterical.  Each home used up
2 IP addresses, one for the modem and one for the PC.  The horrific part
was that you could telnet into any cable modem, the modems were all even
numbers I believe.  You could shut the modems down from the telnet port,
but not much else.  A friend of mine and I were known to sometimes
telnet into each others routers and shut them down occasionally.

> Not to say all their hardware operates the same way.

Thankfully all the hardware is standardized now.  What they choose to do
with it is up to them, of course.

I am sorry that I didn't go to the top of the thread to fully understand
the original poster's problem.

Pat

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