Re: I-D Action: draft-ietf-6man-rfc6434-bis-01.txt

[Lorenzo Colitti <[e-mail]>]

On Mon, Jul 3, 2017 at 5:40 PM, <[e-mail]> wrote:
>
> A New Internet-Draft is available from the on-line Internet-Drafts
> directories.
> This draft is a work item of the IPv6 Maintenance of the IETF.
>
>         Title           : IPv6 Node Requirements
>         Authors         : Tim Chown
>                           John Loughney
>                           Timothy Winters
>         Filename        : draft-ietf-6man-rfc6434-bis-01.txt
>

I see that the document still says:

   There will be a wide
   range of IPv6 deployment models and differences in address assignment
   requirements, some of which may require DHCPv6 for stateful address
   assignment.  Consequently, all hosts SHOULD implement address
   configuration via DHCPv6.

We should abandon this documentation, for two reasons.

First, networks that require DHCPv6 assignment are explicitly NOT
RECOMMENDED by current IETF best practices. Specifically, RFC 7934 section
8 says "it is RECOMMENDED that the network give the host the ability to use
new addresses without requiring explicit requests". A DHCPv6-only network
cannot meet this recommendation, because on a DHCPv6-only network, all
addresses acquisition requires an explicit request to the network.

Second, the draft says "Where devices are likely to be carried by users and
attached to multiple visisted networks, DHCPv6 client anonymity profiles
SHOULD be supported as described in [RFC7844]".

But RFC 7844 says that hosts SHOULD prefer stateless address configuration
over DHCPv6: "hosts using the anonymity profile SHOULD use stateless
address configuration instead of stateful address configuration".

So for such devices, there is a direct conflict: this document says they
SHOULD do DHCPv6, but RFC 7844 says they SHOULD not if other addressing
modes are available.

I would propose the following text for section 6.5:

   [...] There will be a wide
   range of IPv6 deployment models and differences in address assignment
   requirements, some of which may use DHCPv6 for stateful address
   assignment in addition to other addressing modes. Using DHCPv6 as the
   only IPv6 address configuration mechanism is NOT RECOMMENDED
   [RFC 7934 section 8].

   In the absence of a router, IPv6 nodes using DHCP for address
   assignment MAY initiate DHCP to obtain IPv6 addresses and other
   configuration information, as described in Section 5.5.2 of
   [RFC4862].

   Where devices are likely to be carried by users and attached to
   multiple visisted networks, DHCPv6 client anonymity profiles SHOULD
   be supported as described in [RFC7844] to minimise the discolosure of
   identifying information. This profile recommends that the device prefer
   stateless address configuration over DHCPv6 address configuration.

   Devices that do not have particular anonymity requirements SHOULD
   implement address configuration via DHCPv6 in order to be able to
   take advantage of IPv6 addresses available only via DHCPv6.