Cable modems are designed to fit to a standard called DOCSIS (Data Over Cable Service Interface Specification). DOCSIS 2.0 was introduced in 2001 while DOCSIS 3.0 was introduced in 2006 with support for higher speeds and has been slowly rolling out for the last 8 years. Comcast has traditionally supported both at the same time.
In general, when a customer signed up for Comcast (now Xfinity) high speed internet service, Comcast would provide the customer with a leased modem. In exchange for paying a monthly fee (around $5-8), Comcast would replace the modem if there were any problems. Most customers chose to do so.
Some of PMUG’s more technical members may have chosen to save money by purchasing a modem for themselves and foregoing the rental fee.
It appears that Comcast is ending support for DOCSIS 2.0 modems, and so some very long term customers of Comcast are getting cut off. If you are one of these people, you may be forced to buy a newer modem.
If you are having any troubles, then come ask the Apple “Smarties” at the upcoming PMUG General Meeting on June 9th.