Home Hub - No LAN IPv6 Address when IPv6 Allocation set to none.

[ravenstar68]

Hi

I am attempting a rather unique home setup where I have a device on my home network act as IPv6 router and then pushes packets to the BT hub LAN  Link Local IPv6 address and they go on to the internet from there.

To achieve this I have a Linux box set up with ISC running DHCPv4 Bind running DNS and RADV and RDNSS set up sending RA's advertising the /64. Once this was running I set the BT Hubs IPv6 address allocation to none.  My understanding is that you cannot have 2 devices on the same network sending out RA's

This worked for an hour or 2 then after a while I lost IPv6 connectivity.

Going back to the Hub I noted that the LAN side GUA was ::

Previously it was a GUA in the hubs /64 with the same host part address as the link local

i.e.

Link Local:  fe80::c6e5:32ff:fe36:4d36/64

GUA:      2a00:xxxx:xxxx:xxxx:c6e5:32ff:fe36:4d36/64

This meant that packets lo longer had a clear IPv6 path to and from the internet AFAICT.

Turning Allocation to stateless and back to none restored the LAN side address until the address lifetime presumably given by the BT hub expires and then returns back to ::

My question is - is this by design?

I understand the possibility of the /56 and consequently the /64 changing down the line however should that happen my network will still retain IPv4 capability.  However conceptually what I had set up WAS working until the hubs IPv6 LAN address vanished.

I would have hoped that the LAN side would have picked up the RA's from my linux box and configured the LAN IP using the advertised /64 or at the very least have an autoconfigured static address.

Thoughts would be welcomed here.

Thanks in advance.

[Edinburgh-wg]

If your hub establishes an internet connection, I'm unclear why you switched off ipv6 on it. How is your Linux box to handle ipv6 queries - except on lan - if there is no ipv6 address? 

[WSH]

If the BT hub is sat between your Linux box and BT, how is the Linux box to get a global prefix from BT?  If it is disabled, the BT hub won’t generate its own RA, and it can’t pass on any it gets from BT.

Perhaps I’ve misunderstood what you are trying to do.

[ravenstar68]

To be honest I can understand your confusion and after writing my post I actually concluded that my setup would not work.  Although it might end up being achieved a different way.  Which I will look into at some point.

As you may be aware the hub has a /56 allocated to it.  The first /64 is used to provide the WAN side address and the second /64 is used to provide the LAN side addresses.

I wanted to move complete control of DNS server advertisements to my own network rather than using BT's DNS - why because I never liked the fact that BT along with other ISP's don't honour DNSSEC or that they openly spoof DNS when NXDOMAIN is received.

Whilst the LAN had configured itself with the information provided by BT - it provided on onward route to the internet.

I configured the Linux box with an IP in the hubs LAN range set up manually.

The idea of setting up RA's on the box was that I could advertise a route to the router gateway and with RDNSS included my devices could set up DNS automatically.

In retrospect had my system done what I had hoped - it could have ended up with a routing loop on my network.  So I have knocked it on the head.

My main issue I suppose is we have BT voice and my understanding is that in order for this to work - I have to use the BT Hub - although I do have one of the Wifi phone adapters.

The only other question is - If I set IPv6 address allocation to stateful - i.e. DHCPv6 - would it be possible to turn off DHCPv6 on the BT hub and instead have my own DHCPv6 setup on Kea in linux - much like I have disabled IPv4 and am currently running my own on ISC - soon to be migrated to Kea

[licquorice]

Much simpler to just use a Raspberry Pi and PiHole to provide DNS and DHCP instead of the hub.

[WSH]

If you use a third-party router as a subnet inside the Smart hub 2, the third-party router can get a global IPv6 as a DHCP client of the SH2 and then provide its own DNS settings.  I was doing that for many years with a Draytek 2762.

Unfortunately, the 2762 is now obsolete.  The 2767 I bought as a replacement does have difficulty passing an IPv6 prefix from the SH2 to the LAN.  Last time I spoke to them, Draytek where looking into this problem for me but I subsequently decided to ditch the SH2 and go with third-party VoIP.  (I was never happy about being tied into ISP equipment again because of DV).  As such, I don't know whether Draytek have now fixed the problem.  Unfortunately, Draytek are another firm that are not what they once were.

[Crimliar]

Okay, I'm probably being incredibly incredibly stupid here...  IPv6 is off on the BT router itself, so prefix-delegation is going to fail (as already mentioned), but even if that were fixed, surely there'd be no IPv6 gateway either because that would have been the BT router?

*With different hardware, use can be made of differing /64 subnets!

[Edinburgh-wg]

@ravenstar68 

You should replace your BT hub with a third party router that allows you to edit upstream DNS server information (from what I remember, you can't edit DNS server information on the hub). DrayTek has gone to the dogs and its firmware is now compulsively buggy - avoid this brand altogether. If you require a European brand, FritzBox ticks the box as it's made in Germany and has simple, yet effective, GUI that will satisfy all your needs. 

You then enter your RPi/Linux machine's IP address (on LAN) into the DNS server information on the router and then you let RPi/Linux machine (with installed AdGuard or PiHole) handle DNS queries (via IPv4/6).

You must remember to provide your RPi/Linux machine with a fixed IP address on your LAN, and even better, connect via an ethernet port, rather than WiFi (if you use 5GHz, there's the radar detection for DFS channels which can 'lose' the RPion your LAN), as otherwise, you risk not being able to have your queries resolved after a lease time expires. 

So, that's all you require, and nothing as convoluted as you're presenting it to be. (And what you're describing in your subsequent post is very confusing and probably unnecessary in terms of set-up.) 

Here's a guide on how to configure PiHole on Fritzbox to handle DNS queries: https://docs.pi-hole.net/routers/fritzbox/ although what I described above is a much more basic and, most importantly, working configuration, too. (With Fritzbox, not AdGuard/PiHole, functioning as DHCP.) 

[Crimliar]

I read this completely differently, and assumed something more akin to trying to implement NATv6.  I think that gets us back towards the likes of Draytek and business grade suppliers.