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Message 1 of 32

BT Smart Hub IPv6 Stateless forced DNS options


With regard to IPv6 enabled BT Home Hubs and Smart Hubs.

Please could I ask that the option to manage IPv6 is consistent with the options to manage IPv4 to allow for BT customers to manage DNS on both IP protocols?

IPv4 local/private addressing using DHCP can be completely disabled on the Home/Smart hubs allowing for the management of addressing and options to be provided by another service other than the Home/Smart hub. With IPv4 RFC1918 addresses that are NAT'd, it's fair to say that they'll never change on the home side of the router, this is good an reasonable, thank you. It's important to reiterate IPv4 RFC1918 addressing will likely never change on the home LAN so complete handoff of IPv4 RFC1918 address management to another device is possible.

However, with regard to IPv6 GUA addresses that could change at the behest of the network configuration, the BT Smart/Home Hub plays a more important role in the dynamic addressing of the downstream devices. It's the only thing in the network that authoritatively knows what the IPv6 GUA prefix is and should be at any point in time after BT remote reconfiguration/restarts etc. It's therefore reaasonable this device plays the role of the router providing ICMPv6 Router Advertisements with GUA prefix information to the home network to which devices are connected.

The specific issue is the ENFORCEMENT of the ICMPv6 Option when using both Stateless (most urgently), and Stateful IPv6 addressing options in the Advanced configuration.
This is a stateless RA packet from a Smart Hub 2, stateful shows the same option so I won't repost.
The stateless RA has the M and O bits set to 0 and 1 respectively which is fine.
Note the offending option set in bold

Internet Control Message Protocol v6
Type: Router Advertisement (134)
Code: 0
Checksum: 0xf488 [correct]
[Checksum Status: Good]
Cur hop limit: 64
Flags: 0x40, Other configuration, Prf (Default Router Preference): Medium
0... .... = Managed address configuration: Not set
.1.. .... = Other configuration: Set
..0. .... = Home Agent: Not set
...0 0... = Prf (Default Router Preference): Medium (0)
.... .0.. = Proxy: Not set
.... ..0. = Reserved: 0
Router lifetime (s): 180
Reachable time (ms): 0
Retrans timer (ms): 0
ICMPv6 Option (Prefix information : {GUA}::/64)
ICMPv6 Option (Recursive DNS Server fe80::d686:60ff:fe80:d6c4)
ICMPv6 Option (MTU : 1492)
ICMPv6 Option (Source link-layer address : d4:86:60:80:d6:c4)

I feel quite confident that the inclusion of the RDNSS option is not an IETF RFC requiremenet otherwise that would cause tension in Enterprise and Service Provider equipment.

So to allow your customers to manage DNS on BOTH IP protocols which is key to privacy and a great deal of threat management whilst still enjoying the service provided by the Home/Smart Hubs and the WiFi options that allow for excellent coverage without going to market for third party equipment could I please ask that this IPv6 option is removed to make IPv6 and specifically DNS management consistent with the IPv4 management of the devices. I would really appreciate this being considered in future firmware upgrades to the Smart/Home Hubs and to be updated as to the consideration of the request.

Kind Regards

Tags (3)
Message 2 of 32

Re: BT Smart Hub IPv6 Stateless forced DNS options


Please bear in mind that this is only a BT Residential Customer to Customer forum, so any requests posted here, will not go to BT.

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Message 3 of 32

Re: BT Smart Hub IPv6 Stateless forced DNS options

Thanks Keith,

Specifically then, do you know the right route to raise this request through? If you could share - if you know - then perhaps others with the same concern could follow the same route using the same language to mount pressure for the change.


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Message 4 of 32

Re: BT Smart Hub IPv6 Stateless forced DNS options


BT do have a team which deal with these sorts of things. All I can do is to ask a moderator to respond here, and perhaps offer to pass the question to them.

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Message 5 of 32

Re: BT Smart Hub IPv6 Stateless forced DNS options

Thanks! Looking forward to hearing from you.
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Message 6 of 32

Re: BT Smart Hub IPv6 Stateless forced DNS options


I am just a customer. The moderators are the only employees here, and they may reply on this thread.

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Message 7 of 32

Re: BT Smart Hub IPv6 Stateless forced DNS options

@paulby and @Keith_Beddoe I've emailed a contact in the hub team highlighting this thread.



Message 8 of 32

Re: BT Smart Hub IPv6 Stateless forced DNS options

Hi Neil,

What did the hub team come back with? 
I’m happy to raise the request formally through other more appropriate channels if it would make a more coherent outcome. 
Do let me know.


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Message 9 of 32

Re: BT Smart Hub IPv6 Stateless forced DNS options

I'd love to know what this is about!
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Message 10 of 32

Re: BT Smart Hub IPv6 Stateless forced DNS options

The intricacies of IPv6, which is totally different to IPv4 in operation. 

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