Re: [v6ops] [dhcwg] IPv6-Only Preferred DHCPv4 option

Hi Bjørn, 

Blindly releasing the IPv4 address when an IPv6 connectivity is available is problematic because the host does not know if a NAT64 function is available for a given network attachment. A host that discovers the presence of NAT64 (because a pref64 was discovered) can safely release any assigned IPv4 address. No additional signal is needed in such case.

Jen, do you have a case where you want to deploy IPv6-only host without announcing pref64 to that host? 

Cheers,
Med

> -----Message d'origine-----
> De : dhcwg [mailto:dhcwg-bounces@ietf.org] De la part de Bjørn Mork
> Envoyé : mercredi 4 décembre 2019 14:31
> À : Jen Linkova
> Cc : dhcwg@ietf.org; V6 Ops List; draft-link-dhc-v6only@ietf.org
> Objet : Re: [dhcwg] IPv6-Only Preferred DHCPv4 option
> 
> 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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