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Uncapping, The makings of a Semi-Myth

An Editorial by Thomas (Bouncer) Blakely
2000-08-04 (updated: 2009-11-01) by
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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:

  1. The modem "ranges" for useable download/upload frequencies that no one else is using.
  2. Having found useable frequencies, it contacts the Cable Modem Termination System, (CMTS) sometimes called the headend.
  3. The headend responds with some information, one part of which is the address and name of a configuration file.
  4. 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.
  5. The modem applies this file internally.
  6. The modem then authenticates these settings with the CMTS.
  7. 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:

  1. No one can simply plug a modem in and start using the service.
  2. To make sure the service caps are enforced.
  3. 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.


Thomas (Bouncer) Blakely, CCNA, CCDA

  User Reviews/Comments:
by free speech - 2006-08-26 15:01
You omitted however that the "bandwith" as you call it, was public domain until a monopolistic ownership auction was held. Remember that photo op of Clinton and Gore holding that BIG CHECK? Do some more research before you point fingers. The fact that families in America pay over a hundred dollars a month to cable companies is a testament that they are victims of the advertizing they used to get for free. If it was a level playing field, and true competition there would not be such gouging, and people would not on a broad scale need to surreptitiously "get their money's worth".
by NADDDD - 2007-12-19 11:18
The administrations of this site have written quite a bias editorial here. Written seven years ago, if you search for uncapping this is still the first result. What fails to be realized in this article, is that most users who are pests, don't uncap their modem, and ISPs still ban them from their networks. 99% of users will use about 100gb /mo or less, and if your provider sees you breaking this limit, whatever it is that they have determined is appropriate, you will end up banned. This is because ISPs generally pay their carriers in the amount of transfer used, the not speed it is used at. So they would much rather you check email at 1000gbits/sec, than run torrents solid at 1mbps 24/7. If you were to max out your anemic 1meg connection for a month, you would use 259.2 gigabytes of bandwidth, and would be destructive to your neighbors at all hours of the day. Now conventional wisdom would say that if someone were able to download at 10mbits then they would use 2592gb/mo, but if they were to use even 10% of that, their isp would almost definitely take action. More likely, that person with his new found speed would download his torrents at night when network load is low, and in the morning would power down his computer because his downloads were finished, leaving the network available until that night using about the same amount of bandwidth. Cable companies do not want their networks disrupted, and if someone wants a lower ping for a low bandwidth use, or to download the same things they always have much faster then the network is not being disrupted. I encourage readers of this article to also read: you may not agree, but some very good points are made.
by chubbysumo - 2008-04-17 17:40
Uncapping is quite a reality, as there are people who have dedicated their time to it. It is possible with almost any modem and service, and in fact, its not illegal to uncap or modify your OWN modem and hardware. The problems arise when the equipment isnt yours(you rent from your ISP), then its vandalism, and destruction of property(even if its just software/firmware mods), and when said uncapper goes to use this modified equipment on their ISP's network, its considered theft of service, which is still theft, and in most cases is a violation of the ToS agreement and contract with your ISP(even though no number is assigned to what you can use) if you get caught uncapping, there are most likely CIVIL penalties(meaning you get sued by your ISP), and most ISP's will only take it to criminal court if they think that they have a great case. So its not the uncapping thats illegal, its the use. Read your ISP's Terms of Service agreement, and contract very carefully, as most have sections that say that you cannot host your own tftp server(which is what your DOCSIS coble modems get their limit info from) and that all equipment used on your ISP's network has to and can only accept config files from them. I have read charters ToS, and its in there. That said, it means on any charter communications connection, uncapping will get you banned from any charter service for life, at the least.
by anonymous - 2018-07-05 00:04
How could the bandwith have been public domain before the internet went public?
by anonymous - 2018-07-05 00:14
The ISP has to protect their other customers right of access regardless of what time of day or night it is. If you have 20 users on a node, and one or two of those users are using so much bandwidth that other users get slowdowns or get kicked off the network, that generates customer complaints and if a customer complains enough times it won't be long before they start looking for other alternatives. It's not worth it for the ISP to lose 18 or 19 customers for the sake of the one or two who are uncapping.

It doesn't even have to be a case of uncapping, either. Someone on the node could be operating a file server and sharing movie and music downloads and their server is getting so many hits that they slow down the network for everyone else. This is why I am actually in favor of tiered access at different price points. If you're a low usage user, then you pay less than the guy operating the file server and that is only fair. If the guy operating the file server sees his monthly bill skyrocket, then it will force him to reconsider the amount of bandwith he is using. As long as everyone is paying the same, then there will always be people wanting to get more than everyone else because their higher usage is subsidized by the rest of us.
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