Is this for IPv6 there is a separate forum for that. Please post your question there including what you are seeing and what your modem model is.
This is a question about this specific modem. Our current Netgear modem does support prefix delegation, but it freezes frequenly and needs someone to manually power cycle it. We want to replace it and this Cisco 3941 is the only option Comcast is giving us. We have to be sure it properly supports prefix delegation before installing it or our network won't work correctly when they make the change. So my goal is to find out ahead of time if this model modem properly supports prefix delegation (some modems don't). Surely someone at Comcast can answer this?
The 3941 will hand out 2601:: addrtesses to devices connected directly to it, but it will not support "sub-delegation" to a downstream router.