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Re: [v6ops] IPv6-Only Preferred DHCPv4 option

Bjørn Mork <bjorn@mork.no> Wed, 04 December 2019 13:31 UTC

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From: Bjørn Mork <bjorn@mork.no>
To: Jen Linkova <furry13@gmail.com>
Cc: dhcwg@ietf.org, draft-link-dhc-v6only@ietf.org, V6 Ops List <v6ops@ietf.org>
Organization: m
References: <CAFU7BAR1JLUZps=CAqJfeQtUf-xQ88RYvgYrPCP+QP0Ter7YFg@mail.gmail.com>
Date: Wed, 04 Dec 2019 14:31:17 +0100
In-Reply-To: <CAFU7BAR1JLUZps=CAqJfeQtUf-xQ88RYvgYrPCP+QP0Ter7YFg@mail.gmail.com> (Jen Linkova's message of "Wed, 4 Dec 2019 23:09:08 +1100")
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Archived-At: <https://mailarchive.ietf.org/arch/msg/v6ops/jQzgfKQTZfPKmRluZlrwy9hfel8>
Subject: Re: [v6ops] IPv6-Only Preferred DHCPv4 option
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Jen Linkova <furry13@gmail.com> writes:

> Hello,
>
> One of the biggest issue in deploying IPv6-only LANs is how to do it
> incrementally, when some hosts work just fine in NAT64 environment
> while some legacy devices still need IPv4. Doubling the number of
> network segments (having an IPv6-only and dual-stack segments of each
> type) is an operational nightmare. So it would be just awesome if all
> devices can co-exist in the same network segment and hosts capable of
> operating in IPv6-only environment do not consume IPv4 addresses.
> So here is the draft proposing a new DHCPv4 option to help saving IPv4
> addresses and deploying IPv4-as-a-service:
>
> Name:           draft-link-dhc-v6only
> Revision:       00
> Title:          IPv6-Only-Preferred Option for DHCP
> Document date:  2019-12-04
> Group:          Individual Submission
> Pages:          9
> URL:
> https://www.ietf.org/internet-drafts/draft-link-dhc-v6only-00.txt
> Status:         https://datatracker.ietf.org/doc/draft-link-dhc-v6only/
> Htmlized:       https://tools.ietf.org/html/draft-link-dhc-v6only-00
> Htmlized:       https://datatracker.ietf.org/doc/html/draft-link-dhc-v6only
>

  "While IPv6-only capable devices might use a
   heuristic approach to learning if the network provdes IPv6-only
   functionality and stop using IPv4 if it does, it might be practically
   undesirable.  One important reason is that when a host connects to a
   network, it does not know if the network is IPv4-only, dual-stack or
   IPv6-only.  To ensure that the connectivity over whatever protocol is
   present becomes available as soon as possible the host usually starts
   configuring both IPv4 and IPv6 immidiately.  If hosts were to delay
   requesting IPv4 until IPv6 reachability is confirmed, that would
   would penalize IPv4-only and dual-stack networks, which does not seem
   practical. "


Why can't the client just release the IPv4 address when it finds it has
IPv6 connectivity?  This would also avoid the problems you introduce
when the network falsely claims IPv6 support.



Bjørn

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