Re: [v6ops] ULA precedence [Thoughts about wider operational input]

[Mark Smith <[e-mail]>]

On Mon, 25 Apr 2022, 21:45 Ted Lemon, <[e-mail]> wrote:

> On Apr 25, 2022, at 06:03, Erik Auerswald <[e-mail]>
> wrote:
>
> And all that would probably not preclude constructing a different
> scenario where choosing GUA over ULA as source address would break
> connectivity.
>
>
> The question is not what possible scenarios are there, but what scenarios
> do we want to address with default behavior versus what scenarios can we
> only address with managed behavior. So e.g. not using longest-match for
> ULAs with different global identifiers sounds like a good default behavior,
> but obviously will break in some scenarios; in these scenarios, clearly we
> need support for configuring source address selection (which we already
> know how to do). Preferring GUA source address over ULA makes sense by
> default, I think, even though it is not always going to be the right thing
> to do.
>


Defeats a significant purpose of ULAs.

RFC4193:

4.2 <https://datatracker.ietf.org/doc/html/rfc4193#section-4.2>.
Renumbering and Site Merging

   The use of Local IPv6 addresses in a site results in making
   communication that uses these addresses independent of renumbering a
   site's provider-based global addresses.



> Thus I would rather suggest to consider if making tracking which
> gateways advertised which prefixes mandatory would be a better
> approach.
>
>
> That's nice, and again would probably produce better default behavior. But
> I suspect it doesn't solve as many problems as you're hoping it will. E.g.
> what happens if the link you're connected to is one hop away from the link
> to which both of your upstream providers are connected? Now you have one
> router advertising everything, so this doesn't help.
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