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

[Tim Chown <[e-mail]>]

On 15 Apr 2024, at 09:05, Ole Troan <otroan=[e-mail]> wrote:

On 11 Apr 2024, at 05:30, Lorenzo Colitti <lorenzo=[e-mail]> wrote:

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.

You could say this of many MUSTs in many documents, and many implementations. T’was ever thus.

Anyway, something to consider is that now we’re proposing “SHOULD” for the known-local insertion, which is still a strong statement, should we make the default position in the draft for implementations that do NOT do this to leave ULAs as they are now, at precedence 3 (or 20, it doesn’t matter), below GUA and IPv4?  Which would mean the only change in practice to the default policy table would be the 6to4 demotion.

This would mean only implementations that insert known-locals would prioritise ULAs, but they would prioritise them more than they do now, i.e. above GUAs.

Currently the draft changes the default for ULA-ULA to be precedence 30, so above IPv4-IPv4 (precedence 20) but below GUA (precedence 40).

Tim