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Networking/Ethical Hacking Are you a hacker? Then prove it here!

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Old 23-09-2008, 04:58 AM
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Waqas Ahmed will become famous soon enough
Lightbulb Truth About Uncapping the DSL and Cable Modems

Usually illegal, always unethical and generally a violation of your contract, "uncapping" refers to removing the download or upload bandwidth cap imposed by your cable or xDSL ISP.

Uncapping xDSL.

Three words: "Don't even bother".

xDSL technology doesn't work in a way that permits you to have any settings that diverge in the slightest from what you're supposed to have. Any differences and the system cuts you off. Period. This is because xDSL is shared at the DSLAM and not on the medium. Each line is treated as a individual connection, and configured as such. You get what you pay for. And no more. Cable, on the other hand, works differently.

Uncapping Cable.

Cable is a shared medium, each area it serves is somewhat like a LAN.

This means there's X amount of bandwidth for ALL the users on the node to share, and there's a lot of bandwidth. Now, there is a LOT less upstream bandwidth than down, for a variety of technical reasons I won't go into, just understand it is a necessary part of the design. Some people feel cheated by this and want a way around this inherent limitation. Some other folks just want their share of the bandwidth, YOUR share of that bandwidth, and MY share as well, as much as they can get away with and damn the consequences to everyone else.


Not really, but then again we're talking about people you can't see, and apparently it's okay in some folks' mind to steal from others, as long as they can't see them. It's an infantile "nyah-nyah-nyah I can't see you so you don't exist so this has no consequences" type behavior.

My dog is smarter than that. She at least has figured out that even if she can't see something, it might still be there. Apparently though, the "reality is defined only by what I *see*" thing is about as heavy a concept as some folks can handle. Anyways, back to "uncapping".

The Myth.

Unfortunately there is this persistent urban myth that simply changing one or two 'super secret settings' somewhere on some 'hidden interface' will magically turn any cable or xDSL modem into WOPR from Wargames. Giving it the ability to: Control nuclear missiles remotely, Blazing fast downloads and uploads, 2 millisecond pings to the MIR space station, and play a helluva game of Tic-Tac-Toe while it's at it! Now, all good urban myths have some tiny kernel of fact, and this one does as well.

The Origin.

See, in one or two older NON-DOCSIS systems, using a particular brand of modem and one version of firmware it WAS possible to put the modem into a sort of "router bypass" mode, and ignore configuration instructions, by ignoring the CMTS. A clever fellow created a program and a series of instructions to do just that against the European cable provider UPC. That was pre-DOCSIS though.

CMTS? DOCSIS? What are they, and what are the facts?

The Facts.

So you know, DOCSIS is the "Data Over Cable Service Interface Specification". It's a standard that governs how cable modems behave and interoperate. The majority of systems out there, especially from the big cable ISPs, are DOCSIS compliant. The rest are headed that way.

The upside is that if you own your modem, and move to a new locality, if they are DOCSIS compliant you can use the same modem regardless of what kind they normally lease or sell. The downside is that boo-hoo, you can't steal from others. No uncapping.

The reason it doesn't work is that under DOCSIS, the modem goes through a whole series of steps before you are ever allowed on line. The short version is as follows:

After power is applied:

The modem "ranges" for useable download/upload frequencies that no one else is using.
Having found useable frequencies, it contacts the Cable Modem Termination System, (CMTS) sometimes called the headend.
The headend responds with some information, one part of which is the address and name of a configuration file.
The modem goes to this address at the headend and downloads the configuration file which contains IP addresses, cap settings, and a whole host of other signalling and troubleshooting instructions.
The modem applies this file internally.
The modem then authenticates these settings with the CMTS.
NOW it may begin to transmit.
As you can see, it's a complicated process, and until it's complete, you MAY NOT transmit data. Period. It's also periodically refreshed. The modem recieves the "config settings" file every so often from the CMTS and re-applies the settings, making any changes the new settings may dictate. This means that system adjustments can be done on the fly, which is an advantage from a systems management perspective.

There are multiple reasons why it's so complicated. Remember that the process must make sure that:

No one can simply plug a modem in and start using the service.
To make sure the service caps are enforced.
It's also designed to allow for reliability throughout the system so that no singular haywire modem is jamming the entire spectrum and taking down multiple users.
Finally, each modem MAY have it's own file. So that if you buy a work account, you might have more access than your neighbor with the home account. You pay more for that of course. This is a business after all. So that's the brief version of the DOCSIS system, and why uncapping it is a semi-myth.

As to the guy who wrote the "uncapper" program?

Last we heard, he was headed into court on some fairly serious charges. And the firmware has long since been fixed.

The Conclusion.

It would be easier if "uncapping" were simply a myth end to end, then I wouldn't have to explain all this. Point is still the same though. If you have DOCSIS, you get what you pay for. Stop trying to steal from your neighbors, they'll be happier and you'll be happier. And you won't have to go to court on 'theft of service' or possibly Federal equipment tampering charges.

On a personal note I'd like to extend my thanks to all the engineers who've taken time out of their schedules to detail the inner technical working of DOCSIS to me, and to my fellow Moderators and the Administrator here at for all their help as well. Any errors are my responsibility. As always, if you have RFCs or white papers on DOCSIS or related specs on this subject I'd love to take a look at them.

Regards !!!

Waqas Ahmed

My education, expertise and experience as follows:
MS (CS), M.Sc.(TS), CCNA, CCNP, RHCE (prepared),
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VMWARE Server. Windows 2003 Server, Apache Server, Squid Server, etc.
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