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adly
Aspiring Expert
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Message 1 of 10

BT Smart Hub IPv6 Settings

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Hi all,

 

Does anybody know if it is possible to configure the IPv6 settings with the Smart Hub? Specifically, is it possible to disable DHCP for IPv4 but leave it on for IPv6? This was possible previously with my Sky Router and was really handy as I run my own DHCP server and dealing with the prefix delegation for IPv6 is just too messy.

 

--Adam

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smf22
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Message 2 of 10

Re: BT Smart Hub IPv6 Settings

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The IPv4 and IPv6 configuration are separate in the GUI and in terms of what they do so I'm going to say that's possible, but I think it would break things.

 

The way IPv4 addresses are given out is via DHCP. The DHCP server also tells the client the DNS server address, default router address etc.

 

With IPv6 on the Hub 6 the client uses something called Stateless Address Autoconfiguration (SLAAC). Essentially the Hub advertises the IPv6 prefix it's been assigned and the client works out it's own IPv6 address from that. 

 

With the current BT setup, even for IPv6 name resolution the client still uses IPv4 to query the name server. BT DNS servers don't yet support IPv6. So if you turn of IPv4 DHCP, I don't believe your clients will be able to resolve names.

 

What is it you're actually trying to achieve?

 

Regards

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adly
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Message 3 of 10

Re: BT Smart Hub IPv6 Settings

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@smf22,

 

Thanks for the response; sounds like it should work in theory then. The previous Sky setup used DHCPv6 rather than SLAAC which simplified matters. 

 

One of the reasons I like to run my own DHCP server is ISPs never allow the DNS server to be changed and are very fixed in their configuration. I have previously looked into all handling IPv6 via my own DHCP server but it seemed to be a mess when dealing with dynamic prefixes from the ISP, otherwise I'd implement both.

 

I'm basically trying to keep my existing network architecture but with BT Infinity. I know it is 'possible' (though the help page here says it isn't) to use a custom router but it seems to be a minefield, especially with BT TV/multicast. I also don't want to loose native IPv6 support.

 

--Adam

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adly
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Message 4 of 10

Re: BT Smart Hub IPv6 Settings

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@smf22,

 

Actually looking at the Sky setup again (it's been a while), it looks like it's SLAAC with DHCPv6 for configuration (stateless). Perhaps the BT Smart Hub uses a similar setup and disabling DHCP would allow a standalone DHCP server to take over the stateless DHCPv6 configuration?

 

If this is the case then it appears that it should be possible to use the Smart Hub with a custom DHCP server. Indeed, my existing setup could be this way but due to laziness I've not touched the IPv6 router config as of yet. Smiley Embarassed The only issue would be if BT instead use ND RDNSS as using a custom DHCP server would break IPv6.

 

--Adam

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smf22
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Message 5 of 10

Re: BT Smart Hub IPv6 Settings

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Sounds like what you want is simple enough, and essentially what I run here.

 

My setup is a Ubiquiti EdgeRouter (via OpenReach modem) and this runs my own DHCPv4 server for multiple VLANs / networks (HomeLAN, HomeWiFi, GuestWiFi etc.). The DHCP server offers OpenDNS, but you can make this what you like as long as BT parental controls etc., are disabled.

 

Each VLAN I have is also enabled for IPv6, but uses SLAAC for client addressing. This gets around the issue you mention with DHCPv6 when the prefix changes. In this setup the clients simply use the IPv4 DNS server that I give them to get the IPv6 AAAA record.

 

In IPv6 there's also an option to have the router tell the client to determine it's IPv6 address vian SLAAC, but to use a DHCPv6 server to get 'other' information such as an IPv6 DNS server, time server etc. Again my EdgeRouter does this, but I haven't got around to doing it yet.

 

Ubiquiti is not for everyone as the GUI is pretty basic and you need to get down and dirty with the CLI to make it really work. But there are plenty of other routers out there that will do the same or similar.

 

The point about BT not supporting anything other than Hubs etc., only really matters when you need their 'support'. I keep one in the cupboard and put it in place if and when needed.

 

Regards

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AndyCoffin
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Message 6 of 10

Re: BT Smart Hub IPv6 Settings

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Question: is the ipv6 even working yet on the smarthubs? im my config screen it says hub and network staust enabled but DNS as being not available. i also know that while i have 5 ipv6 compatible devices only 2 are being issues with v6 address's via the hub but im sure they are still connecting via v4 as typeing in addresses that are ipv6 only are very hit and miss, sometimes they work and sometimes not

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smf22
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Message 7 of 10

Re: BT Smart Hub IPv6 Settings

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Hi @AndyCoffin. Today the Hub 6 does support IPv6 and has been available since October 2016.

 

BT DNS servers don't yet support IPv6, but that's not really an issue as the IPv4 DNS server will return both an A (IPv4) and AAAA (IPv6) record for a name.

 

The Hub doesn't issue IPv6 addresses as such. What it does is tells the clients by way of an IPv6 Router Advertisement (RA) the IPv6 network prefix they are part of, and the client uses a mechanism called Stateless Address Autoconfiguration (SLAAC) to determine the host portion of the IPv6 address.

 

Regards

AndyCoffin
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Message 8 of 10

Re: BT Smart Hub IPv6 Settings

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Interesting thanks, so if a device supports v6 its the device that needs to get the address and not the router to issue it? I ask as we have 2 samsung s5neo's and a network printer (amongst other things) all have v6 enabled on automatically get address but only 1 of the phones and our main pc is being shown via the hubs gui as being issued with one
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smf22
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Message 9 of 10

Re: BT Smart Hub IPv6 Settings

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Correct. The router tells the clients the 'prefix' and the client will work out it's own IPv6 Global Unicast Address (GUA). The Hub will periodically send a Router Advertisement (RA), but what should happen is that when a client connects to the network it will send a Router Solicitation message, to which the Hub will immediately respond with the RA. This is so the client doesn't have to wait for the periodic RA.

 

I'm not sure I'd rely on what the Hub 6 GUI is telling you. You only have to look at the mess it makes with the IPv4 addresses of DHCP and Static.

 

Is there a way to see the IPv6 address on the device? You should see it have an address starting 2a00:23xx if it's working correctly.

 

Regards 

AndyCoffin
Aspiring Expert
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Message 10 of 10

Re: BT Smart Hub IPv6 Settings

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Im not at home at the mo. Will investigate when i do and report back. Thank you for the input
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