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

Jen Linkova <furry13@gmail.com> Thu, 05 December 2019 01:00 UTC

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References: <CAFU7BAR1JLUZps=CAqJfeQtUf-xQ88RYvgYrPCP+QP0Ter7YFg@mail.gmail.com> <da078a21-b606-f0d9-3833-d66b20410853@marples.name>
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From: Jen Linkova <furry13@gmail.com>
Date: Thu, 05 Dec 2019 12:00:43 +1100
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To: Roy Marples <roy@marples.name>
Cc: dhcwg@ietf.org, draft-link-dhc-v6only@ietf.org, V6 Ops List <v6ops@ietf.org>
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Subject: Re: [v6ops] [dhcwg] IPv6-Only Preferred DHCPv4 option
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Hi Roy,

On Thu, Dec 5, 2019 at 11:30 AM Roy Marples <roy@marples.name> wrote:
> > 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:
>
> I disagree with a fair chunk of this.
> It assumes that IPv6 is the be-all and end-all. Maybe one day we will
> have IPv8?

Oh I do hope that by the time we start deploying IPv8-only networks
we'll be done with IPv4 ;))
On a serious note: if one day we discover that we also have other
scenarios (in addition to IPv6-only networks) when we might want to
provide IPv4-as-a-service, the proposed mechanism still can be used I
believe.
While the draft keeps mentioning IPv6-only and NAT64 as a prerequisite
for disabling IPv4, it's only because it's the only use case exist
today.
If I wake up tomorrow to find out that we have IPv2020 and majority of
my devices can operate on IPv2020-only while I still have to provide
IPv4 for some hosts, we can do 's/IPv6/IPv2020/g' in the text.

> It would be much better to say that DHCP as a whole is disabled.

Sorry, I'm not sure I understand. The draft is proposing that if a
client is willing to live w/o IPv4 and the server confirms that IPv4
is optional on the network segment, the client is disabling DHCP for
some time.
What would you like us to change?

> See RFC 2563 for an equivalent DHCP option for IPv4LL. This is fair
> enough because it's all IPv4 addresses. Set both options and you're golden.
>
> BUT - what if we need to enable DHCP again? Should clients still listen
> for FORCERENEW? It does pose a small dilema because there isn't actually
> anything to renew.

The draft covers that scenario. DHCPv4 is disabled for V6ONLY_WAIT seconds.

-- 
SY, Jen Linkova aka Furry