Re: [IPv6] Second Working Group Last Call for <draft-ietf-6man-rfc6724-update>

[David Farmer <[e-mail]>]

You say, "In these cases, we will get the old behavior, which works well
enough."

However, RFC6724 is not implemented universally or entirely. Therefore, the
current behavior, or the old behavior compared to this update, is a mix of
RFC3484, RFC6724, and a hybrid of the two in gai.conf.

Moreover, you and others might feel RFC6724's behavior is good enough, but
at least many of those instigating this draft think preferring IPv4-IPv4 or
ULA-ULA is incorrect behavior and contrary to the intent of preferring IPv6
to IPv4.

It would be best for all IPv6 implementations to implement known-local
ULAs. The normative language best suited to accomplishing that is
debatable; I'm fine with SHOULD or MUST, with a slight preference for MUST.

Nevertheless, any implementation that does not implement known-local ULAs
should raise the ULA label's preference above that of the IPv4 label. Give
that at least most implementations that use gai.conf already do that that
is not inconsistent with the current behavior works good enough.

Thanks

On Mon, Apr 15, 2024 at 8:02 AM Ted Lemon <[e-mail]> wrote:

> What should says is the the behavior is not optional—we don’t think there
> is a good reason for an implementation not to do the behavior.  Which is
> true here.
>
> It’s also true, as you say, that not all prefixes will be identifiable as
> local in all cases.  In these cases, we will get the old behavior, which
> works well enough.
>
> Op ma 15 apr 2024 om 04:06 schreef Ole Troan <[e-mail]>
>
>>
>>
>> > On 11 Apr 2024, at 05:30, Lorenzo Colitti <lorenzo=
>> [e-mail]> wrote:
>> >
>> > On Thu, Apr 11, 2024 at 1:04 AM Ted Lemon <[e-mail]> wrote:
>> > I continue to think that section 3,  "Operational Issues Regarding
>> Preference for IPv4 addresses over ULAs," should make the new proposed ULA
>> behavior mandatory rather than optional. I don't see a downside to making
>> it mandatory. Hosts will come into compliance when they can; older
>> implementations will not implement this new behavior, but I don't see any
>> point in perpetuating that.
>> >
>> > Absolutely agree. This document should not proceed without that MUST.
>> Preferring non-local ULA over IPv4 is incorrect because IPv4 implies global
>> reachability, and ULA does not offer global reachability. So publishing
>> this document without the MUST is harmful: an implementation that does not
>> implement the SHOULD will cause regressions and break use cases that work
>> today.
>>
>> A host should not make those assumptions.
>> A RFC1918 IPv4 address may or may not have global reachability.
>> A ULA may (or may not) have global reachability.
>>
>> In essence SA/DA combination can be assumed to provide reachability. It
>> has to be probed.
>> The _only_ thing SAS/DAS selection should be used for is ordering of the
>> candidate list.
>>
>> > Also, MUST allows us to make ULA more useful than it is today. It is
>> *desirable* to be able to publish non-local ULAs and have hosts know what
>> is local and what is not. As a simple example: once all hosts implement the
>> MUST, it will be safe to publish local ULAs in the global DNS, because
>> hosts won't try to use them unless they are local.
>>
>> That’s likely a simplification. As they are certainly going to be
>> networks where there will not be possible to signal all ULA prefixes to
>> every host.
>> The IETF conviction that as long as we make something a MUST then every
>> implementor will implement it is flawed. The only thing it does is to water
>> out the value of the MUST. Any MUST/SHOULD debate motivated by this (as
>> opposed to a real interoperability breaking issue) is bike-shedding.
>>
>> O.
>>
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