Can I uncap my cable modem ?

Uncapping refers to the concept of somehow lifting the bandwidth cap many cable modem service providers (MSO's) impose. Some users want to do this in order to improve the speed of their cable modem, obviously circumventing the service provider and may be considered theft of service. Some early pre-DOCSIS cable modems could be hacked to remove upstream limitations, however, those days are long gone. Still, some cable modems can potentially be uncapped using one the following methods:

TFTP - setting up a modified DOCSIS config file on a TFTP server, and somehow tricking the cable modem to read the config file from the Ethernet side. This is against the DOCSIS specs, however, various older modems were vulnerable to this, taking advantage of the fact that some MSOs did not enable authentication checking at the CMTS.

Shell access - many modems have some type of shell for debugging purposes. This is typically a simple telnet/serial command-line interface, enabling control over parameters internal to the cable modem. This could include blocking of automatic firmware upgrades, changing the MAC address, etc.

Fake MACs - by changing the MAC address (and possibly serial number) to that of another user, once can potentially steal that users' service. More than one cable modem with the same MAC can be logged at the CMTS and the MSO can track this down fairly easily.

IP accumulation - the idea being that some cable ISPs appear to limit bandwidth on a per IP basis. So, if a user finds a set of unused IPs, they can change to them instead of using DHCP and pool bandwidth that way. The normal (DOCSIS supported) way of imposing a cap on the individual users bandwidth is by setting this in the config file to make the cable modem rate limit it's own upstream bandwidth. This method only works for some MSOs that used to rate-limit upstream bandwidth at the router instead (typically done by defining tunnels, like PPPoE, for each cable modem and applying a bandwidth cap on those tunnels).


Notes: This information is not intended as an uncapping tutorial. All speed tweaks on this site (changing TCP Receive Window, etc.) to improve speed are not considered "uncapping" and are absolutely legal way of fixing/tuning your OS to improve network performance.