This topic

IPv6 prefix delegation from Smart Hub 2 to LAN

cetus — Mon, 16 Oct 2023 21:57:32 GMT

Hello,

I'm trying to set up an IPv6 subnet in my LAN and am wondering how I can get a global prefix for it.

I understand BT delegates a /56 to me and would like to get one of the 254 spare prefixes (/64) routed via the Smart Hub 2 down to my router on the LAN.

The only relevant setting I found on the Hub side is 'IPv6 address allocation mode', which can be set to Stateful, Stateless, Both, or Off. I set it to Both, tried soliciting a prefix via DHCPv6-PD, and got a refusal – my dhcpcd says:

DHCPv6 REPLY: No prefixes available for this interface.

Has anyone had any luck with this kind of thing? Or is there a static route configuration in the Hub somewhere or something that I may be missing?

Many thanks.

Re: IPv6 prefix delegation from Smart Hub 2 to LAN

WSH — Mon, 16 Oct 2023 22:05:12 GMT

I just set the SH2 to stateless and my own router to DHCPv6 client. Seems to work fine.

Re: IPv6 prefix delegation from Smart Hub 2 to LAN

sp11 — Sun, 18 Feb 2024 11:26:55 GMT

Nope it doesn't work... the prefix length is fixed to /64 and cannot be changed. It means that the router is NOT delegating the network prefix... useless.

Re: IPv6 prefix delegation from Smart Hub 2 to LAN

c64z86 — Sun, 18 Feb 2024 11:42:08 GMT

I don't know if this will help, but I have a secondary router connected to my SH2 via its WAN port.

For IPV6 to work I had to enable "pass through(bridged)" mode on the secondary router, on the IPV6 page itself, (NOT putting the router in bridged mode), and then reboot both of them.

When everything came back up I had full IPV6 support on my devices, my router even threw in an IPV6 Google DNS for me to make up for BT's lack of such a DNS!

So really it is just letting the SH2 handle all the IPV6 stuff as the primary router. Leave it on the default of stateless.

Re: IPv6 prefix delegation from Smart Hub 2 to LAN

WSH — Sun, 18 Feb 2024 12:13:41 GMT

@sp11

Perhaps I'm imagining things then.

@c64z86 Makes a good point about the bridging the IPv6. I did forget to mention that.

Re: IPv6 prefix delegation from Smart Hub 2 to LAN

sp11 — Sun, 18 Feb 2024 16:21:40 GMT

What you guys are actually doing is to convert your second router into a simple hub. The first router is not doing ipv6 prefix delegation, instead, it is simply assigning ipv6 addresses to all of your devices (because the second router is simply passing forward all your devices requests to the first router).

With a proper prefix delegation, your first router would assign a network prefix to your second router (/60 for example) so your second router would have a proper range of IPs to assign to the devices.

Re: IPv6 prefix delegation from Smart Hub 2 to LAN

c64z86 — Sun, 18 Feb 2024 16:43:13 GMT

Ah ok. I only understand the very basics of IPV6, and even then I'm still stumped by a lot of it. For me, as long as it's working on my devices then it's ok and nothing else needs to be done lol.

If you don't get much help here, you might want to give the r/homenetworking sub of Reddit a try as well. The guys there are very knowledgeable about IPV6 and a lot more to do with networking, so someone there should know just what you need.

Re: IPv6 prefix delegation from Smart Hub 2 to LAN

WSH — Sun, 18 Feb 2024 16:59:34 GMT

No, my devices set their own IP with SLAAC. I do see your point, however. My second router is using the IP provided by the SH2 but it is then effectively only providing the network prefix to the LAN and the devices generate their own host address. In fact, Windows devices generate a temporary address on a 24 hour basis anyway.

I would be curious as to what your solution is though, and why you think that would work better?

Re: IPv6 prefix delegation from Smart Hub 2 to LAN

sp11 — Sun, 18 Feb 2024 17:25:14 GMT

I'm not saying my solution is better, I'm just pointing out that ipv6 prefix delegation is not an option for SH2. Just answering the original question. About the reasons why I was looking for prefix delegation is that I want to be as independent as possible from BT. I have my own infrastructure and I don't want to change it just because of SH2. I don't want to have to go to SH2 whenever I have an issue with ipv6 and I want to be able to switch to another provider whenever I want without having to change my own infra.

Additionally, I don't want any ISP eavesdropping my network traffic and I don't trust ISP router's firmware since it can be managed remotelly by the ISP's and who knows what they can do with your network.... so I'm changing to business BT hoping that their modem can be configured as modem only (or bridge mode) and use a VPN on my own router so the traffic will be encrypted. If BT business router doesn't work as expected I'll need to buy a VDSL modem.

Re: IPv6 prefix delegation from Smart Hub 2 to LAN

WSH — Sun, 18 Feb 2024 17:38:59 GMT

Ah, right. My original answer was a suggestion as to how to get IPv6 working. I know it’s not true PD.

“Stateless” DHCP should only be providing the prefix and gateway/DNS addresses. The hosts should be autogenerating their own addresses. I don’t think the SH2 can do true delegation, (and I need the SH2 in the loop for Digital Voice), so this is the next best thing.

The arrangement works well as BT can manage their “connection” but my own router still manages my network and guards the gateway to my LAN.

Before DV I was using my own router. If you are using your own router, just setting the IPv6 to Native PPP works.

And on the paranoid note, even with your own router the traffic still goes through the ISP and can be monitored. (In fact, up to a point, they’re obliged to under the IPA). If you are that concerned about snooping, use a VPN and hope the provider is honest about not keeping logs.

Re: IPv6 prefix delegation from Smart Hub 2 to LAN

c64z86 — Mon, 19 Feb 2024 01:37:14 GMT

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!

Re: IPv6 prefix delegation from Smart Hub 2 to LAN

WSH — Mon, 19 Feb 2024 10:06:44 GMT

@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.

Re: IPv6 prefix delegation from Smart Hub 2 to LAN

c64z86 — Mon, 19 Feb 2024 11:17:57 GMT

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.

Re: IPv6 prefix delegation from Smart Hub 2 to LAN

WSH — Mon, 19 Feb 2024 11:59:17 GMT

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.

Re: IPv6 prefix delegation from Smart Hub 2 to LAN

c64z86 — Mon, 19 Feb 2024 12:13:41 GMT

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

Re: IPv6 prefix delegation from Smart Hub 2 to LAN

WSH — Mon, 19 Feb 2024 12:29:56 GMT

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.

Re: IPv6 prefix delegation from Smart Hub 2 to LAN

c64z86 — Mon, 19 Feb 2024 12:46:53 GMT

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! 😮

Re: IPv6 prefix delegation from Smart Hub 2 to LAN

WSH — Mon, 19 Feb 2024 12:51:54 GMT

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.