Re: [v6ops] Updating RFC 7084

I'll paraphrase my comment on SNAC about this, because we had a good
discussion there and I think this is actually more of a v6ops thing than a
SNAC thing (there's debate on the SNAC mailing list about whether we'd want
to do multi-homing even if the infrastructure supports it).

DHCPv6 PD assumes that the network is managed by a single entity, and so if
the network is multihomed, you can communicate with a single DHCPv6 server
and get all the information you need. There are a lot of reasons why this
is no longer correct. The first is that DHCPv6 doesn't (and can't) support
Provisioning Domains (PvDs). The second is that a very likely scenario for
a multi-homed home network (if any such scenario is at all likely!) is that
you have two CE routers connected to the same link, each of which is
advertising an RA on the link. Hosts on the link see both RAs and are
therefore multihomed.

RFC7084 doesn't talk about the PvD RA option for the simple reason that the
document that describes it was written long after 7084. Now that we have
such an option, it seems like an excellent way to indicate that the network
is multi-homed: each CE router can advertise a different PvD. How they are
defined is something we'd have to figure out, but in principle this seems
like a reasonable approach.

Why do we care? Because probably a DHCPv6 PD /client/ should be trying to
get one PD per PvD, not one PD total. A DHCPv6 PD client that doesn't do
this is only ever going to get a PD from one of the two CE routers, and
which one it gets isn't going to be deterministic. So this is a really
clear limitation for multi-homed networks in this scenario. RFC7084-bis
could clarify how this works, and I think it should. It's possible that
we'd also need a document in the DHC working group talking specifically
about the DHCPv6 PD behavior in the presence of multiple PvD RAs.

On Fri, Nov 18, 2022 at 9:47 AM Timothy Winters <tim@qacafe.com> wrote:

> Hello,
>
> I've started a draft to update RFC 7084 to support prefix delegation on
> the LAN interfaces.  The current state of IPv6 in home networks is ISP are
> assigning prefixes of appropriate sizes but they currently are under
> utilized due to the lack of prefix delegation on LAN interfaces.
>
> This draft is an attempt to add that support to the draft.
>
> https://datatracker.ietf.org/doc/draft-winters-v6ops-cpe-lan-pd/
>
> This is only an update to 7084 at the moment, there has been some
> discussion on the snac working group about leveraging this work as well.
>
> One item being discussed is this currently doesn't solve multi-homed
> networks.
>
> I welcome any feedback about the proposal.
>
> ~Tim
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