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Message 41 of 47

Re: BT IPv6 with third party router

@licquorice wrote:

Is that the router WAN address or LAN address? I think what is happening on the TP Links is that the WAN doesn't get an address but the LAN gets a /64 address along with connected devices.

And devices connected to TP-Link modem/routers like my VR600 end up with working 128 bit IPv6 addresses - although possibly more by luck than judgement Smiley Happy.



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Message 42 of 47

Re: BT IPv6 with third party router

@conrad wrote:

@stevebrass wrote:

I have had no luck with a Billion 8800, but an ASUS RT AC51U performs impecabbly with IPV6.

billion_fan on the billion forum has been able to get an IPv6 connection on his 8900AX-2400 on BT infinity 2 but the confusing thing is that the address is /64  not the expected /56.

BT hand out a /56, but then the router should assign a /64 to it's LAN interface and advertise that same /64 in it's Router Advertisement on the LAN.


Here's part of a tcpdump packet capture of the DHCPv6-PD reply received by my router on the PPPoE interface:



    Message type: Reply (7)
    Transaction ID: 0xf61d35
    Identity Association for Prefix Delegation
        Option: Identity Association for Prefix Delegation (25)
        Length: 41
        Value: 0000000000093a8000127500001a001912cc030012cc0300...
        IAID: 00000000
        T1: 604800
        T2: 1209600
        IA Prefix
            Option: IA Prefix (26)
            Length: 25
            Value: 12cc030012cc0300382a0023c55501bd0000000000000000...
            Preferred lifetime: 315360000
            Valid lifetime: 315360000
            Prefix length: 56
            Prefix address: 2a00:23c5:xxxx:6e00::


In the above we can see BT assigned my router a prefix length of /56 and the prefix of 2a00:23c5:xxxx:6e00.


On my LAN interface the address is as follows:


smf22@erx:~$ show interfaces
Codes: S - State, L - Link, u - Up, D - Down, A - Admin Down
Interface    IP Address                        S/L  Description
---------    ----------                        ---  -----------
switch0                  u/u  Home LAN


The router is using the 6401::1/64 i.e., the first /64 subnet within the /56 that BT assigned.


I'd say the behaviour of the Billion 8900AX-2400 looks to be correct.



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Message 43 of 47

Re: BT IPv6 with third party router

@smf22 - So what do you make of what my VR600 is doing? Running ipconfig on my Windows PC, I get the following (with random letters of the alphabet concealing real values in places):

(a) an IPv6 address of 2a00:23c1:xxxx:yy01::2
(b) another IPv6 address of 2a00:23c1:xxxx:yy01:aaaa:bbbb:cccc:dddd
(c) a temporary IPv6 address of 2a00:23c1:xxxx:yy01 followed by a different last 64 bits from (b) above.
(d) a link local IPv6 address of fe80:: followed by the same last 64 bits of my IPv6 address in (b) above.


My Macbook shows 2 IPv6 addresses (one is the temporary version) with the same first 64 bits as on my PC but the rest different; and says "Prefix length = 64".


My poor confused VR600, on the other hand, shows:


WAN side: IPv6 address of ::

LAN side: IPv6 address of 2a00:23c1:xxxx:yy01:! (sic); Prefix Length=64; Assigned Type=Delegated.


Do you think the VR600 is receiving 2a00:23c1:xxxx:yy::/56 but expecting /64, therefore sticks 01 on at the end as the first (and only) subnet?



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Message 44 of 47

Re: BT IPv6 with third party router

I agree with @smf22's analysis.

The /56 denotes the size of the address block that BT is delegating to the customer, and it's a superset of the /64 block that is assigned to the router's default LAN, namely the LAN served by the router's own switch.

A /56 prefix is delegated so that each customer can configure up to 2^(64-56) == 2^8 == 256 different /64 networks within that large /56 address space. This is described in RFC 6177, the intention being that "smart homes" can be structured as many different /64 networks within the delegated address space, or indeed networks of any size between /64 and /56.  That /64 is merely the base block which the router creates for its default LAN without needing to be told, and that will suffice for many people.  Any further LANs need to be set up by the user manually.

The Billion 8800 does appear to be working correctly.

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Message 45 of 47

Re: BT IPv6 with third party router

@prinknash: Yes, that would be my guess too. The only theory I have why it might be assigning "01" as the bottom two hex digits of a /64 prefix is if it thinks that "00" is already taken, and the only reason that comes to mind why it might think that is if it misinterprets a ...:yy00/56 as a ...:yy00/64.

The technical term for this is "b0rked".
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Message 46 of 47

Re: BT IPv6 with third party router

@MorgaineD wrote:

The technical term for this is "b0rked".

Indeed. Although, as I've said, my various PCs, laptops and handheld devices all seem to be accessing the internet using native IPv6 quite happily. So I'd be inclined to categorise IPv6 as working on the VR600 but in a slightly limited and not very graceful manner.


At least TP-Link have acknowledged the problem and committed to solving it.



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Message 47 of 47

Re: BT IPv6 with third party router

Indeed. IPv6 is quite forgiving in that respect, as there is no need for each subnet's last address to be bound by listeners for response to ARP query broadcasts --- that just breaks IPv4 stone dead.  Because of its automatic link-local addresses, IPv6 is pretty much plug'n'play without needing configuration, somewhat like USB, so it'll make life much easier for non-techies.

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