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Re: Confirmation to advance: draft-ietf-6man-ipv6only-flag-05

David Farmer <farmer@umn.edu> Thu, 23 May 2019 22:14 UTC

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In-Reply-To: <ce07ade8-5105-055f-4798-f4ef20a2393c@si6networks.com>
From: David Farmer <farmer@umn.edu>
Date: Thu, 23 May 2019 17:13:50 -0500
Message-ID: <CAN-Dau02MYCrKx2BgyuYJeHBdoz6SHCnp+-byM+LMM8af0S+rA@mail.gmail.com>
Subject: Re: Confirmation to advance: draft-ietf-6man-ipv6only-flag-05
To: Fernando Gont <fgont@si6networks.com>
Cc: Philip Homburg <pch-ipv6-ietf-6@u-1.phicoh.com>, 6man WG <ipv6@ietf.org>, Fernando Gont <fernando@gont.com.ar>
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On Tue, May 21, 2019 at 11:38 AM Fernando Gont <fgont@si6networks.com>
wrote:

> If I understand correctly, you were arguing that IPv4 SD should be
> disabled by default for IPv6 only networks.
>

In my opinion, what he is saying is not about IPv6-Only, because without a
flag a host can't know it is on an IPv6-only network.

What he is saying is a dual-stack host that has functioning IPv6 should not
enable IPv4 LL. And functioning IPv6 means at a minimum it has learned an
IPv6 GUA and probably a default router as well, you could also test for
connectivity beyond the default router, but that

The risk this creates is that on a dual-stack network if a there is an
issue with the DHCPv4 server, such as it crashed or was misconfigured then
the dual-stack host cannot fall back to IPv4 LL and will not be able to
perform Link-Local communications with IPv4-Only devices on the common link
between them.

Personally, I think this is an acceptable risk, but I'm not convinced that
there is a consensus that this is an acceptable risk. Therefore, I'm not ok
with abandoning the IPv6-Only flag until there is a consensus that this is
an acceptable risk. Furthermore, we need more than 6man's consensus on this
risk.


> For the average user, this means that if they actually needed, now they
> are in trouble.
>

Yep, there is a non-zero risk of problems.

-- 
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David Farmer               Email:farmer@umn.edu
Networking & Telecommunication Services
Office of Information Technology
University of Minnesota
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