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Cable modem boot process on an AT&T-based "SAS" provisioning system (which Insight uses):

1) Modem ranges through multiple frequencies to find the downstream frequency that the CMTS uses.
2) With the downstream frequency locked, the CMTS broadcasts a packet that tells the modem what upstream frequency to use.
3) Once the modem locks onto the upstream, it can send its MAC (hardware) address to the CMTS, which routes the MAC info to SAS in New Jersey or thereabouts.
4) If the SAS system recognizes the MAC as being registered to an active account, it allows the SAS TFTP server to send a config file to the modem as specified on the account.
5) The SAS DHCP server assigns an IP to the modem, based on the CMTS to which the modem is connected.
6) The modem downloads the config file, telling the modem what speeds are allowed, what ports to enable, how many PC's (if using a hub) can connect behind the modem, and other related things.

For Insight, the basic residential config is 3000Kbps down, 128Kbps up, and 7 PC's allowed. The next tier's config is 3000Kbps down, 384Kbps up, and 7 PC's allowed.

In summary, the CMTS doesn't hold config files nor does it assign IP's. Each CMTS has one or more IP scopes that basically tell it how to route traffic coming from one of those IPs (cable modems). The CMTS does the traffic shaping and speed capping according to what your modem's config tells it. So, if you hack your cable modem's IP and it doesn't fit in the scope on the CMTS, good luck checking your online horoscope.

This information was pulled from a thread in the /forum/mediacom forum. The original thread is here /forum/remark,8713408~mode=flat VoIPster gets the credit for posting the details. The information confirmed as correct here /forum/remark,9343160~mode=flat

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by IGGY See Profile edited by fukitol See Profile
last modified: 2004-02-11 13:10:17