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

Lorenzo Colitti <> Sat, 18 November 2017 08:47 UTC

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From: Lorenzo Colitti <>
Date: Sat, 18 Nov 2017 17:46:42 +0900
Message-ID: <>
Subject: Re: New Version Notification for draft-hinden-ipv4flag-00.txt
To: james woodyatt <>
Cc: Bob Hinden <>, IPv6 List <>, Fernando Gont <>
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On Sat, Nov 18, 2017 at 11:20 AM, james woodyatt <> wrote:

> Wouldn’t you think setting 4=1 to be a good idea in that case? Alas, it’s
> not. If we do that, then any dual-stack hosts on a network with an
> IPv4-only CE router will shut off their IPv4 activity, and they will not
> get any IPv6 service through us. This is probably not what anyone wants, so
> we would of course never ever, not in a million years, never send 4=1 in
> our RA messages.

Yep, a single flag won't work unless all routers agree on it. What about an
option that signified there was no IPv4 on the network? If the option is
sent by any of the routers on the link, then hosts would not attempt IPv4

Not sure how that would support IPv4 becoming available once the option has
been set. Also, not clear how to deal with the DOS scenario where a rogue
RA disables all IPv4 on the network until the end of time.