Re: 64share v2

Lorenzo Colitti <lorenzo@google.com> Wed, 11 November 2020 08:48 UTC

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From: Lorenzo Colitti <lorenzo@google.com>
Date: Wed, 11 Nov 2020 17:48:34 +0900
Message-ID: <CAKD1Yr0tDTSH2F4=ZsdMJREy1k6equ9mZV0Au1bJPmKuzxeYVA@mail.gmail.com>
Subject: Re: 64share v2
To: Ole Troan <otroan@employees.org>
Cc: Ca By <cb.list6@gmail.com>, 6man WG <ipv6@ietf.org>
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On Wed, Nov 11, 2020 at 4:28 PM <otroan@employees.org> wrote:

>  - the PIO is used for prefix discovery on the directly connected link, a
> different option
>    "delegated prefix option" should be created. A principle of good
> protocol design is to be explicit
>

+1. We can't just change the length of the PIO from 64 to 60, since this is
really not the same as a PIO. A PIO specifies "the prefixes that are
on-link and/or are used for stateless address autoconfiguration". Here, the
prefixes are not on-link, and any non-/64 PIO can't be used for autoconf
anyway, because for global addresses, IIDs are 64 bits long. If we just
change the PIO from /64 to /60, IPv6 on existing mobile devices will just
stop working. Also, the A and L bits in the PIO are meaningless. If the
network is delegating a /60 prefix to a mobile device, it makes no sense to
say "you can have this entire /60 but nothing in it can use autoconf", or
even "you can have this /60 and autoconf is available on it".


>  - ND has been designed to be datalink type agnostic. This mechanism
> should not assume a 3GPP link.
>    Needs text to state that this new option requires per client messaging
> or an underlaying p2p link.
>

+1


>  - Unsure if you need some way for the client to refresh or request a
> delegation.
>

Personally I don't think we need a way to do this. For the problem at hand,
the semantics of RAs are fine, it's the semantics of the PIO that don't
meet the needs.


>  - You need to clarify host/router behaviour in that you now make the
> RS/RA behaviour between routers.
>

Not sure that necessarily needs to be added here. After all, we
published RFC 7278 without it, and the problem is basically the same. And
RFC 6204/7084 (IPv6 CE routers) already expects such routers to listen to
RAs.


>  - You should require a mechanism for the CE to verify forwarding state in
> the PE. We missed that in 3315.
>

I don't think this is a problem in mobile networks. Certainly, I don't
think we currently have anything along these lines for IPv4 addresses or
IPv6 /64s.

Instead, I think we should say that the prefix MUST be a superset of a
prefix that already has a PIO with A=1. That would make failure modes very
clear.