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

[Ted Lemon <[e-mail]>]

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.

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.