IPv6 support on Virgin media

@Adduxi:

If you look through your HH6's Event log, which is in the hub's GUI menus at:
         Advanced Settings->Technical log->Event log
you'll find a line containing something like:

WAN DHCPv6 Client Prefix : 2a00:23xx:xxxx:xx00::/56 (valid time = ...

From https://www.bgpview.io/asn/2856#prefixes-v6, BT has a prefix of 2a00:2380::/25
which you can see in the first 6 hex digits (6*4 = 24 bits) of your client prefix.
The 25th bit of their allocation is a 1-bit (bit 3 of hex '8'), so your 'x' hex digits
can be anything as long as the first one starts with a 1-bit, hence '8' through 'f'.

So, altogether there are 14 hex digits = 14*4 = 56 bits in your prefix, matching the /56
mentioned in your Event log. (The "00" just before the :: is not part of your prefix, but
just pushes the two preceding 'x' digits left by 2*4=8 bits.) What that line is telling
us is that BT is delegating to clients a /56 IPv6 block, the same as Sky. According to a
presentation given by Virgin at a meeting of the UK IPv6 Council, this is also the same
as Virgin will provide. (Just as well, as competing on delegation width would be daft.)

The /64 that you observed isn't the client delegation but only the width assigned to the
IPv6 address on the interface connected to the CPE's switch. You can see that on the two
pages Home->Advanced settings->IPv6->Ststus and Home->Advanced settings->IPv6->Configuration.
Those detail the settings on the WAN and LAN sides respectively, the WAN settings being fixed
and the LAN settings being configurable.

A delegation of /56 provides 256 blocks of /64, so in summary what you have is this:

2a00:23xx:xxxx:xx00::/64 - Block 00 - On your HH6's LAN interface and switch
2a00:23xx:xxxx:xx01::/64 - Block 01 - On your HH6's WAN interface
2a00:23xx:xxxx:xx02::/64 - Block 02 - First block available for further routing
.... 252 more /64 blocks
2a00:23xx:xxxx:xxff::/64 - Block ff - Last block available for further routing

Morgaine.