***NOTE: Reposted;  original message didn't make it to the backbone, feed connection issues; now resolved.

Hello Victor!

16 Oct 21 15:35, you wrote to all:

 VS> 2. A /64 on the internal interface of ISP-owned CPE

If appears that 2 is the closest.

Xfinity / Comcast of Dover, Delaware (USA)

I've got a dynamic IPv6 Address on my router WAN side reporting (via a FUGLY web interface):
    WAN IP Address (IPv6): 2001:558:6027:19:c4e3:1bee:faf8:939d
    WAN Default Gateway Address (IPv6): fe80::201:5cff:fe80:6846
    Delegated prefix (IPv6): 2601:48:c500:9340::/64


Interally::
Mac worstation [ifconfig en0] [GbE]
en0: flags=8863 mtu 1500
    options=50b
    ether 14:98:77:33:fb:b5
    inet6 fe80::14ad:ef4c:c045:132f%en0 prefixlen 64 secured scopeid 0x6
    inet6 2601:48:c500:9340::c0e3 prefixlen 60 dynamic
    inet 10.0.0.160 netmask 0xffffff00 broadcast 10.0.0.255
    nd6 options=201
    media: autoselect (1000baseT )
    status: active


Linux 'server' [ifconfig enp2s0] [GbE]
enp2s0: flags=4163  mtu 1500
        inet 10.0.0.219  netmask 255.255.255.0  broadcast 10.0.0.255
        inet6 2601:48:c500:9340:52e5:49ff:fec3:646a  prefixlen 60  scopeid 0x0
        inet6 fe80::52e5:49ff:fec3:646a  prefixlen 64  scopeid 0x20
        inet6 2601:48:c500:9340::7da  prefixlen 128  scopeid 0x0
        ether 50:e5:49:c3:64:6a  txqueuelen 1000  (Ethernet)
        RX packets 967924  bytes 238763058 (227.7 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 986053  bytes 541541895 (516.4 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

[netstat -6 -rn]
    Kernel IPv6 routing table
    Destination                    Next Hop                   Flag Met Ref  Use If
    ::1/128                        ::                         Un   0   11     0 lo
    2601:48:c500:9340::7da/128     ::                         Un   0   4      0 enp2s0
    2601:48:c500:9340:52e5:49ff:fec3:646a/128 ::              Un   0   4      0 enp2s0
    2601:48:c500:9340::/60         ::                         U    2   3      0 enp2s0
    fe80::52e5:49ff:fec3:646a/128  ::                         Un   0   3      0 enp2s0
    fe80::/64                      ::                         U    256 2      0 enp2s0
    ff00::/8                       ::                         U    256 10     0 enp2s0
    ::/0                           fe80::cc83:d8ff:fea0:bbf7  UG   2   9      0 enp2s0


Additionally,  I can ping my router's public IPv6 address from the LAN side, don't know about the WAN side.  I also can make IPv6 connections to sites on the Internet, infact, macOS 11+ default to IPv6 first; and my Linux system has been updated to do the same.

Cheers,
Scott


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