Re: [IPv6] I-D Action: draft-ietf-6man-rfc6724-update-06.txt

[Tim Chown <[e-mail]>]

Hi,

On 5 Jan 2024, at 21:10, Brian E Carpenter <[e-mail]> wrote:

On 05-Jan-24 23:22, Tim Chown wrote:
Hi Brian,
On 2 Jan 2024, at 19:56, Brian E Carpenter <[e-mail]> wrote:

Hi,

Now that the slip has been corrected, we have:

7.2.  GUA-GUA preferred over ULA-ULA

as the default behaviour.
Yes, sorry about that, I think we muddled the text over known-locals.

I suggest adding a note that to reverse this preference, an operator MAY change to fc00::/7 45 13 (but that the method in section 5.3 is better).
That’s a good suggestion, thank you.
But this then does beg the question - as per 5.3, 6724 says a host MAY add an entry for a locally observed prefix, which would provide ULA preference in a (simple) site over GUAs and avoid remote ULAs (which might happen to be in the global DNS) being preferred.  In previous discussion the group seems quite split, or at least I’d struggle to see a clear consensus, on whether “known-local” insertion might be the norm, or at least promoted to a SHOULD.  I think that’s something we need to thrash out, else we won’t have consensus to publish.

It's not a trivial thing to add, so it probably couldn't be stronger than SHOULD. I personally think it should be the norm - if an operator enables a ULA prefix, it's presumably because they want hosts to use it!

Personally, I’d like to see this elevated to at least SHOULD. And I agree, without elevating all ULAs above GUAs, the only option seems to be smart insertion of known-local ULA prefixes in the policy table with a precedence higher than GUA, and if the available source and destination addresses include such known-local ULAs those should be used.

Alternatively, and this would be a separate effort, we'd need to standardise a way to update the RFC6724 tables remotely. Maybe we need that anyway.

We have RFC 7078 for DHCPv6, but that’s pretty much not implemented anywhere. I don’t recall anyone proposing an RA-based approach.  There was some discussion about the need for configuration and potential approaches in the (very old!) WG draft that the chairs spotted and since removed from the WG draft list (quite rightly).  It’s https://www.ietf.org/archive/id/draft-chown-addr-select-considerations-03.txt; it was considered a useful thing 10+ years ago to have as a WG item, maybe the topics in here need to be considered again.  Certainly the thinking has evolved, e.g., we now view Rule 5.5 as being rather important.

Tim

  Brian

Re-reading 5.3 I see another “holiday” mistake - fc07::/7, we’ll fix that too, apologies.
Tim

Regards
  Brian Carpenter

On 03-Jan-24 05:42,[e-mail] <mailto:[e-mail]>wrote:
Internet-Draft draft-ietf-6man-rfc6724-update-06.txt is now available. It is a
work item of the IPv6 Maintenance (6MAN) WG of the IETF.
   Title:   Preference for IPv6 ULAs over IPv4 addresses in RFC6724
   Authors: Nick Buraglio
            Tim Chown
            Jeremy Duncan
   Name:    draft-ietf-6man-rfc6724-update-06.txt
   Pages:   14
   Dates:   2024-01-02
Abstract:
   When [RFC6724] was published it defined an address selection
   algorithm along with a default policy table, and noted a number of
   examples where that policy table might benefit from adjustment for
   specific scenarios.  It also noted that it is important for
   implementations to provide a way to change the default policies as
   more experience is gained.  This update draws on several years of
   operational experience to refine RFC 6724 further, with particular
   emphasis on preference for the use of ULA addresses over IPv4
   addresses and the addition of mandatory support for Rule 5.5.  The
   update also demotes the preference for 6to4 addresses.  The changes
   to default behavior improve supportability of common use cases,
   including automatic / unmanaged scenarios.  It is recognized that
   some less common deployment scenarios may require explicit
   configuration or custom changes to achieve desired operational
   parameters.
The IETF datatracker status page for this Internet-Draft is:
https://datatracker.ietf.org/doc/draft-ietf-6man-rfc6724-update/
There is also an HTMLized version available at:
https://datatracker.ietf.org/doc/html/draft-ietf-6man-rfc6724-update-06
A diff from the previous version is available at:
https://author-tools.ietf.org/iddiff?url2=draft-ietf-6man-rfc6724-update-06
Internet-Drafts are also available by rsync at:
rsync.ietf.org::internet-drafts
_______________________________________________
I-D-Announce mailing list
[e-mail] <mailto:[e-mail]>
https://www.ietf.org/mailman/listinfo/i-d-announce <https://www.ietf.org/mailman/listinfo/i-d-announce>

--------------------------------------------------------------------
IETF IPv6 working group mailing list
[e-mail] <mailto:[e-mail]>
Administrative Requests:https://www.ietf.org/mailman/listinfo/ipv6 <https://www.ietf.org/mailman/listinfo/ipv6>
--------------------------------------------------------------------