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

Michael Richardson <> Fri, 17 November 2017 14:49 UTC

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From: Michael Richardson <>
To: IPv6 List <>
cc: Bob Hinden <>
Subject: Re: Fwd: New Version Notification for draft-hinden-ipv4flag-00.txt
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Date: Fri, 17 Nov 2017 09:49:51 -0500
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Bob Hinden <> wrote:
    > 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

Didn't we do all of this in sunset4 two years+ ago? I'm sure Lorenzo or Jen
remembers the debate and will correct my mis-representations.

I don't recall what happened to that work.

There is/was real pressure to tell the zillions of v4 machines on the cable model
networks to stop with the DHCPv4 queries, because they took up bandwidth.

Some had religious misgivings about using IPv6 to say something about IPv4.

The security consideration discusson went something like this:
    - this is a trivial DOS if there is really an IPv4 network
    - hosts that want to do v4 must therefore take this as advice, rather
      than gospel, and try the IPv4 anyway.
    - since they will try the IPv4 anyway, the goal of shutting them up

However, I am enthusistic about such a flag, even if it is advice only and
everyone has to ignore it for security reasons.  It announces a desired
policy for the router issuing it.  It says, "I do not offer native IPv4"

It can moderate the hosts' enthuasiam for finding an IPv4, can ask the human
for advice, and if you want to mount a DOS against the IPv4 network, just use
DHCPv4 as people do now.

Michael Richardson <>ca>, Sandelman Software Works
 -= IPv6 IoT consulting =-