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

David Farmer <farmer@umn.edu> Wed, 22 November 2017 00:42 UTC

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From: David Farmer <farmer@umn.edu>
Date: Tue, 21 Nov 2017 18:42:22 -0600
Message-ID: <CAN-Dau0TfDedocjOTkaoiHxDQNemCbTY9Q1in1wqHGoMdYdnHQ@mail.gmail.com>
Subject: Re: problem statement [was Re: New Version Notification for draft-hinden-ipv4flag-00.txt]
To: Brian E Carpenter <brian.e.carpenter@gmail.com>
Cc: Nick Hilliard <nick@foobar.org>, Lorenzo Colitti <lorenzo@google.com>, IETF IPv6 Mailing List <ipv6@ietf.org>
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On Tue, Nov 21, 2017 at 6:15 PM, Brian E Carpenter <
brian.e.carpenter@gmail.com>; wrote:

> On 22/11/2017 11:33, Nick Hilliard wrote:
> > Lorenzo Colitti wrote:
> >> On Wed, Nov 22, 2017 at 12:47 AM, Nick Hilliard <nick@foobar.org>;
> wrote:
> >>> There would also be a requirement
> >>> for the network edge to be able to filter out RAs with this option,
> >>
> >> Why is it not sufficient to configure the routers that emit the RAs?
> >
> > because you're assuming congruity between ipv4 and ipv6 connectivity on
> > a network, which is not codified in any ietf document that I'm aware of.
> >  If there is a incongruity between management of the two protocols, then
> > the l2 network must have a mechanism to stop an ipv6 gateway from
> > attempting shutting down ipv4 services.
>
> 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 is a problem only if the flag is set automatically and their is no
mechanism to override the automatic setting.  Most routers with an IPv6
address configured on an interface by default will send an RA unless you
configure them not to.  So, an IPv6 router without IPv4 configured on the
interface should set this flag, unless configured otherwise.  In other
words you need to be able to tell an IPv6 router there is IPv4 on the
interface even if router is not providing it.

It is quite possible that the IPv6 topology is incongruous from the IPv4
topology, however it is doubtful than the management is also incongruous.

Thanks

-- 
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David Farmer               Email:farmer@umn.edu
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