Static IPv6 getting a /59 PD on DPC3941B

I'm surprised you're getting a delegation at all with a DPC3941B. The other posts on thsese forums seem to suggest that prefix delegation is completely broken on that device, and I wasn't able to get any delegation working at all on mine, no matter what the hint was. I'm using an ASA 5506-x as the device behind the gateway.

I did chat with Support earlier today on this - they basically said that my gateway was getting a /56 and referred me to the forums for help. Which, needless to say, wasn't really helpful. I have a feeling that v6 support for static customers isn't really fully baked yet.

So, it looks like after configuring the prefix hints correctly I am actually getting a /59 delegation out of the DPC3941B. That's good news, since the other posts in the forum suggest that only the Netgear can do this, and the Netgear CPE only gives out a /60.

Even requesting a /56 gives out a /59 - not bad, since I'm sure the gateway uses at least 2 /64s for internal use.

Right i'm getting the same thing. My whole issue is I want to subdelegate prefixes to routers downstream, but that /59 i'm getting becomes a /67 (because it's initial prefix + 8), and i can't do SLAAC EUI with a 67 so things get a bit ugly. The weird bit is that i do see a /56 everywhere, Gateway and Comcast Business portal, so i "should" be getting that but can't.

Also, and i think this is in line with what you're saying about internal use, the gateway's LAN itself has an address that overlaps with the /56 network, so perhaps that's why it can't delegate the full prefix?

I think that's the case. I'm asking for 2603:3023:81c:c100::/56, which is what's delegated, but getting 2603:3023:81c:c1e0::/59, which suggest that the gateway is reserving 14 /64s for itself.