Hi, On Tue, Aug 05, 2025 at 02:06:33PM -0700, Randy Bush wrote: > > Sort of. I would twist it a bit differently, something with more bias > > on "it's the largest hammer in your toolbox, so use with care" - can't > > find good wording right now. > > local pref may be the largest hammer in one's toolbox, but it deals with > a very different nail than path prepending. it influences only inbound > routes, i.e. where you send packets. this is the inverse of as path > prepending, which influences from where you receive packets.
Which is the crux of local-pref in the context of AS path prepending -
entity A expresses the wish for a path to be less preferrable by
prepending, while entity B decides to force a path "no matter what
the rest wants"...
> the largest hammer in the inbound packet toolbox is deaggregation. as
> with all hammers, skill and a bit of wisdom is advised.
True on the size of the hammer, but in this context, deaggregation usually
happens "on the origin side", so that's a choice on "entity A" side
(and of course entity B can decide to filter deaggregates).
> i am not sure local pref belongs in this document at all, as its title
> is path prepending, not general traffic engineering. but maybe mission
> creep and corner cases are the foundation of the game.
Valid point. Either the document wants to focus on path prepending alone
(in which case the question stands "what is there to be learned from it?")
or it extends itself towards various aspects of TE, and how they interact,
which would then be more informative...
Gert Doering
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