IPv6 prefix delegation from Smart Hub 2 to LAN

[c64z86]

How do I enable bridge mode on my BT Business Hub?

The BT business Smart Hubs can be put into bridged mode.

If you are wanting a 3rd party router, be sure to pick something that is compatible with BT's implementation of IPv6. They do something funky with the prefixes that most other providers do not do. At least that's what I just read on another forum, and how I understood it, so I may be wrong! 

[WSH]

@c64z86  As far as I know they just issue the usual /56, like most ISPs are doing.  As sp11 pointed out, the whole network address/prefix is actually /64 so the other 8 bits are added by the end user for subnetting.  As this is irrelevant for the average home user, it boils down to just adding 01 to the end of the PD.

If you’ve seen something more interesting pray do tell.

[c64z86]

Yes, I'm not sure I understand it fully, but these are instructions if you want to use a TP-Link router directly with BT IPv6 (No Smarthub in between)

"The main issue with using the TP-Link Router to connect to BT’s IPv6 is that it won’t connect using TP-Link’s default settings and according to some BT forum posts it’s due to how TP-Link uses the /64 prefix for IPv6 when the BT uses /56 prefix for IP addresses and there’s no real way to change it."

Although on some of their routers, the firmware has fixed that. For the others you will need to do a workaround.

Although: "After running this setup for a while, I’ve discovered that sometimes, the C50 was unable to get an IPv6 address after a reboot. This can be fixed by toggling the MLD Proxy option off and back on again."

Just something to be aware of.

[WSH]

Sounds like what I was describing.  I'd think that was more of a short-coming on the early TP-Link configuration rather than something unusual on BT's part.  As I understand it, the use of /56 to allow for user subnetting is fairly standard now.  In fact, the original spec was /48 but it was later considered that nobody needed 65000 odd subnetworks and it was dropped to 256.

[c64z86]

Ahh ok, thank you for explaining that!

IPv6 is one strange beast for sure. When I think I have learnt something about it, I find out I was wrong and then have to begin trying to know it all over again lol.

What doesn't help is that /48 allows for more subnets than /56. I'm more used to the bigger the number=the more of it there is/the more it can provide, in the computing world! xD

[WSH]

Not at all.  IPv6 is a far more sensible structure, in fact.

The whole network address, (or more correctly in IPv6, “network prefix”), is /64.  The first half of the address.  It’s always the first half of the address but the reason it is more correctly called the network prefix is because, unlike IPv4, it now comprises of several sub parts.  The first few bits, or format prefix, identifies the type of address.  (A decimal 2 or 3 for a global addresses).  Next is a regional identifier set by IANA.  Then there is a network identifier set by the ISP and lastly those end few bits to identify your subnet.  Very logical.

[c64z86]

Yes, when you put it like that it does seem logical and pretty amazing at the same time!

I've just read that the maximum number of devices that IPv6 supports is potentially in the trillions! Each of those devices having it's own personal IP address! 😮

[WSH]

3.4 x 10 to the power 38 or 3.4 undecillion addresses.  (Compared to IPv4’s just shy of 4.3 billion).

Actually, a correction to my last.  It’s a Hex “2” or “3” not decimal.  The global identifier is actually the address starting with the binary sequence 001.  As each hex character is four binary digits, that is 0010 or 0011, a hex 2 or 3.  I don’t think anyone has issued a 3 yet though.