Re: Confirmation to advance: draft-ietf-6man-ipv6only-flag-05

[David Farmer <[e-mail]>]

On Mon, May 13, 2019 at 4:26 AM Philip Homburg <
[e-mail]> wrote:

> >The problem is, without a flag to clearly designate a network as
> IPv6-Only,
> >then with your proposal if the DHCPv4 server on a dual-stack network ever
> >decides to not grant an IPv4 address to a client, due to a
> misconfiguration
> >or it simply crashes, then that client will inappropriately disable
> >RFC3927.  Whereas with a flag declaring a network as IPv6-Only, RFC3927 is
> >only inappropriately disabled when two misconfigurations or a
> >misconfiguration and a problem occurs.
>
> This strikes me as a bad trade-off. You propose that every network that
> doesn't want IPv4 link local has to set a flag just to help the rare case
> of a DHCPv4 server failing and users able to get useful work done using
> IPv4 link local.
>
> So instead of letting IPv4 die. We would add a flag to IPv6 to help in the
> case IPv4 has a problem. Does that make any sense?
>

I don't propose this, I simply contend that it is what RFC3927 and
dual-stack model intends. Per Section 2 of RFC 4213, the dual-stack model
expects dual-stack hosts to be fully compatible with IPv4-Only hosts.
Further, there are good reasons to require this for compatibility between
dual-stack hosts and IPv4-Only hosts. If dual-stack hosts were to do as you
say and not configure a Link-Local IPv4 address if they have a working IPv6
address they would not be able to communicate with IPv4 Link-Local or
global scope unicast IPv4 addresses on the local link unless they receive a
global scope unicast IPv4 address via DHCPv4. Your proposed change breaks
the dual-stack model.

By the way, do you mean any working IPv6 address? Because all IPv6 host
will have an IPv6 Link-Local address. So, do you mean a global scope
unicast IPv6 address?

Without some kind of explicit signal that a network is intended to be
IPv6-Only, per Section 2 of RFC4213 a dual-stack host needs to be fully
compatible with IPv4-Only hosts that could be on the dual-stack network.

Thanks.
-- 
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