I have an IPv6 /56 assigned to me that I can see on the modem and in my account page, and I have a static IPv4 /29 range that works fine. I'm also in a the Indiana market that Comcast says supports IPv6 statics.
My assumption is that I can use the /56 on my internal network, and there should be a /64 outside of that /56, as in a totally different scope, that my firewall will use for PtP communicaiton between my firewall and the Comcast modem. This way the modem would have a simple routing statement that says that the /56 assigned to me is available at X IPv6 address.
However, I've not been provided that information on the PtP link, and no one at Comcast phone support seems to have it.
Is my assumption correct on how Comcast handles it? Can someone with working IPv6 static chime in please?
I had this working without issue for quite some time with a netgear modem. Essentially you have to do a prefix request on your personally managed CPE, from there you can do what you want with the prefixes, but you won't likely see the /56. I saw a /60 even though I had a /56 assigned in the customer portal and on my modem. The Cisco modem...jury's still out. I can't get it to work at all for anything but a SLAAC address.
Agree on prefix delegation not appearing to work on the Cisco DPC3941B device; I see the static 2603::/56 provisioned in the modem GUI and can get DHCPv6/SLAAC addresses on directly connected devices, but no prefix response to DHCPv6-PD request. Our main CPE device is a Cisco ASA5506-X, but I have also tried a Ubiquiti Edgerouter and a Netgear FVS336G, and PD does not work with any of them.