Re: New Version Notification for draft-hinden-ipv4flag-00.txt

Jen Linkova <> Sat, 18 November 2017 14:40 UTC

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From: Jen Linkova <>
Date: Sun, 19 Nov 2017 01:39:42 +1100
Message-ID: <>
Subject: Re: New Version Notification for draft-hinden-ipv4flag-00.txt
To: Bob Hinden <>
Cc: IPv6 List <>
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Hi Bob,

To be honest I'm not convinced that there is a real problem to be solved..
The draft says

'A mechanism is needed  to inform hosts that there is no IPv4 support
and that they should turn off IPv4.'
and it would be great to have more detailed problem statement IMHO...

It looks to me that when you are saying 'there is no IPv4 support on a
link' you mean 'a router does not provide IPv4 connectivity'.  However
it still might be
IPv4 connectivity within the given broadcast domain and the router has
nothing to do with it.

If the problem is 'IPv4 broadcast noise on the link' then it should be
solved on L2 level and the network should not switch ethertype 0x0800.
If the problem is 'all those noisy DHCPv4 requests the first-hop
router has to drop because DHCP relay is not configured' then the
router interface should not accept IPv4 packets at all, problem

Also it's not clear what a host is supposed to do if it'd been
receiving RAs with that flag set 0 and at some point subsequent RAs
started to arrive with that bit set to 1...
Shall the host stop all IPv4 operations attempts? Basically how that
information could be updated?

On Fri, Nov 17, 2017 at 5:42 PM, Bob Hinden <> wrote:
> Hi,
> Brian and I took a cut a defining an IPv4 Availability Flag for IPv6 ND
> Router Advertisements.  From the Introduction:
>    Hosts that support IPv4 and IPv6, usually called dual stack hosts,
>    need to work on IPv6 only networks.  That is, a link where there are
>    no IPv4 routers and/or IPv4 services.  Monitoring of IPv6-only
>    networks, for example at the IETF 100 meeting in Singapore, shows
>    that current dual stack hosts will create local auto-configured IPv4
>    addresses and attempt to reach IPv4 services.  A mechanism is needed
>    to inform hosts that there is no IPv4 support and that they should
>    turn off IPv4.
>    Because there is no IPv4 support on these links, the only way to
>    notify the dual stack hosts on the link is to use an IPv6 mechanism.
>    An active notification will be much more robust than attempting to
>    deduce this state by the lack of IPv4 responses or traffic.
>    IPv4-only hosts, and dual-stack hosts that do not recognize the new
>    flag, will continue to attempt IPv4 operations, in particular IPv4
>    discovery protocols typically sent as link-layer broadcasts.  This
>    legacy traffic cannot be prevented by any IPv6 mechanism.  The value
>    of the new flag is limited to dual-stack hosts that recognize it.
> We were originally thinking it would be an April 1 submission, but after
> reading the discussion on the IPv6 list, we decided it makes sense as a real
> submission :-)
> Please review and comment.
> Thanks,
> Bob and Brian
> Begin forwarded message:
> From:
> Subject: New Version Notification for draft-hinden-ipv4flag-00.txt
> Date: November 17, 2017 at 2:36:31 PM GMT+8
> To: "Robert M. Hinden" <>om>, "Robert Hinden"
> <>om>, "Brian Carpenter" <>
> A new version of I-D, draft-hinden-ipv4flag-00.txt
> has been successfully submitted by Robert M. Hinden and posted to the
> IETF repository.
> Name: draft-hinden-ipv4flag
> Revision: 00
> Title: IPv6 Router Advertisement IPv4 Availability Flag
> Document date: 2017-11-17
> Group: Individual Submission
> Pages: 5
> URL:
> Status:
> Htmlized:
> Htmlized:
> Abstract:
>   This document specifies a Router Advertisement Flag to indicate that
>   there is no IPv4 service on the advertising router.  This document
>   updates RFC5175.
> Please note that it may take a couple of minutes from the time of submission
> until the htmlized version and diff are available at
> The IETF Secretariat
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SY, Jen Linkova aka Furry