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Re: problem statement [was Re: New Version Notification for draft-hinden-ipv4flag-00.txt]

Nick Hilliard <nick@foobar.org> Wed, 22 November 2017 00:23 UTC

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Date: Wed, 22 Nov 2017 00:23:39 +0000
From: Nick Hilliard <nick@foobar.org>
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To: Brian E Carpenter <brian.e.carpenter@gmail.com>
CC: IETF IPv6 Mailing List <ipv6@ietf.org>
Subject: Re: problem statement [was Re: New Version Notification for draft-hinden-ipv4flag-00.txt]
References: <151090059151.22321.3357672601322845792.idtracker@ietfa.amsl.com> <E838C63E-7612-4AA4-9375-854C184D699E@gmail.com> <CAFU7BAQKoWPcEFQZgU3k_d0gUL4en6d2pyNq1V4RMNZ6HrSG8w@mail.gmail.com> <649be36e-5006-7688-448f-bc2794d6a39c@gmail.com> <CAKD1Yr3WC+vwL_=0PeiJ_D85NqFVTCkb8c83x-ZtGhAbSELGMA@mail.gmail.com> <5A119443.2030108@foobar.org> <CAFU7BASwgLfkO-4kk9-vba_P+jmcFHD5+Hy_7b3cnNkOSv30wg@mail.gmail.com> <CAKD1Yr3pKk22Hkxy4_8YMZYiA4Wwp=6JzdRDKFGdTY1gf=ntfA@mail.gmail.com> <alpine.DEB.2.20.1711200848390.32099@uplift.swm.pp.se> <5A12FBE4.9030101@foobar.org> <alpine.DEB.2.20.1711210647151.32099@uplift.swm.pp.se> <5A144A78.6060108@foobar.org> <CAKD1Yr3oQvkSX7ARxfGQVg08=-PTKRFPg1wz_zUKSSAHmMbyMA@mail.gmail.com> <5A14A9A1.5020803@foobar.org> <ea9f56bb-2334-5a5a-9026-d45c74b41d4b@gmail.com>
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Brian E Carpenter wrote:
> This is a very interesting point. If every IPv6 router on a link believes
> there is no IPv4 router/DHCP service, they would all send flag==1 in the
> proposed solution. So the proposal only works if at least one IPv6 router
> is colocated with an IPv4 router, and therefore knows to send flag==0.
> Oops.

This would lead to a race condition on the client + a requirement for
suitable semantics to be defined in the spec to work out what to do if
mixed signals were received from different ipv6 routers.  This assumes
that you can send out an RA with flag==0 in order to mean that ipv4
should be re-enabled again.

Nick

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