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Re: Running code (Was: I-D Action: draft-ietf-6man-ipv6only-flag-03.txt)

Simon Hobson <linux@thehobsons.co.uk> Wed, 31 October 2018 15:54 UTC

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Subject: Re: Running code (Was: I-D Action: draft-ietf-6man-ipv6only-flag-03.txt)
From: Simon Hobson <linux@thehobsons.co.uk>
In-Reply-To: <20181031154737.3errng2ifcmmzcve@faui48f.informatik.uni-erlangen.de>
Date: Wed, 31 Oct 2018 15:54:50 +0000
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Toerless Eckert <tte@cs.fau.de> wrote:

> I am asserting that routers can can assert whether there are 
> any IPv4 only hosts on the LAN and only when there are none,
> and if the router itself is also not configured to route IPv4
> would it automatically set the v6only flag.

There are TWO really big and in practical terms insurmountable problems there.

Firstly, wanting to deprecate IPv4 (in as far as this flag assists it) is an administrative function. it is not a case of whether there are any IPv4 only devices on the network - as has been mentioned several times, there may well be legacy devices still operating but for most devices "we don't care about being able to talk to them".
If you make this (no IPv4 devices) a pre-condition of setting the flag then it's highly unlikely that you'll ever set it given how many of them there are.

Secondly, an IPv6 only router won't know if there are any IPv4 devices there.

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