said by keason:What cable modem supports more than one dynamic address?
Any standard cable modem (or a bridged gateway) for which the customer is paying for a "c02" (two IP addresses), or a "c05" (five IP addresses) config file.
I have personally had no problems with Comcast's BCI config file allowing me to get up to five simultaneous dynamic IP addresses on a bridged SMCD3G-CCR, an SB6121, or a DOCSIS2 DCM-202.
Here is a log excerpt from my current SB6121 that shows the BCI "c05" config file that is being used:
Here is a current "Addresses" display from the SB6121 that I am currently using with three routers behind it: