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

[Jen Linkova <[e-mail]>]

On Thu, Dec 5, 2019 at 12:12 PM Roy Marples <[e-mail]> wrote:
> It assmues only IPv6.
> I dislike it when different protocol families discuss each other - IPv6
> should not turn off IPv4, likewise IPv4 should not turn off IPv6.
> I would prefer it if Iv6 was not mentioned at all outside of a use case
> for the option.

There is a catch there.
Right now the *only* possible scenario when a host might consider IPv4
optional is that:
1) the host supports IPv6
2) either all applications on that host work in NAT64 environment or
the host is doing 464XLAT.
3) the network provides NAT64.
The host knows if conditions #1 and #2 are met and signals it to the
network, so DHCP server responds 'OK, #3 is met as well'.

Now if we stop assuming IPv6 - even worse, if we stop assuming NAT64
being the only transition mechanism - we might end up in a following
situation:
[host] : dear network, IPv4 is optional for me  (because the host can
work in NAT64 environment)
[ the network] ah great, we've been trying to reduce IPv4 footprint so
we deployed IPv15 and the corresponding transition mechanisms, namely
NAT15-to-4, so I'm not going to give an address.

So the host is willing to make IPv4 optional *conditionally*  and
currently that condition is 'NAT64'. We either explicitly describe
that condition in the draft or - as it's been suggested in the thread
- we start encoding it in the option. So if the option value is '1' it
means 'IPv6-Only with NAT64', value 2 - some other 6-to-4 transition
technology we might invent tomorrow, and 3 - some shiny IPv4-to-IPv15
thingy.

> > The draft covers that scenario. DHCPv4 is disabled for V6ONLY_WAIT seconds.
>
> Is the wait seconds even needed?
> Just set the T2 timer and treat it as leasing the unspecified address.
> Less data on the wire, less churn in DHCP clients. V6ONLY_WAIT provides
> nothing of value as I see it.

I suspect it would complicate the configuration. Currently my lease
time is 30 mins. But I do not want IPv6-only capable clients to come
back so often, so I'd be probably setting V6ONLY_WAIT to a number of
hours. While IPv4 clients will continue to receive short lease time.


-- 
SY, Jen Linkova aka Furry