I got caught up in work and dropped this for a while. I'm back now and I've made a little progress. Xfinity / Comcast is give me a /60 (16 /64 subnets). I have the LAN interface tracking WAN using hex 0. This gives my LAN the address of 2601:abc:abcd:fd00:a236:9fff:fef2:383a . This is the last 0 in fd00. I want to pass down to my layer 3 switch a /61 to split among the other VLANs/subnets on that switch. FYI, the L3 switch is the only device on that VLAN. In pfSense, I've changed to the KEA DHCP backend. In SERVICES > DHCPv6 SERVER, on the LAN interface, I see:
PRIMARY ADDRESS POOL:
PREFIX: Delegated Prefix: WAN/0 (2601:0abc:abcd:fd00::/64)/64
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In PREFIX DELEGATION POOL I'm trying to serve out a /61 (which should be 8 /64 subnets) to the downstream layer 3 switch. I ran a packet capture on the LAN interface and cleared out the IPV6 DHCP client on that VLAN/LAN interface. It looks like pfSense is only sending a single /64 address.
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I'm not sure where to go from here. I think I've got the DHCP server configured correctly. Does anyone have any thoughts on this? Thanks!