Re: [c-nsp] BGP Routes

Gert Doering via cisco-nsp <[email protected]> Sun, 12 Mar 2023 19:58:28 +0100

Newsgroups	gmane.network.nsp.cisco
Message-ID	<[email protected]>

Hi,

On Sun, Mar 12, 2023 at 08:51:36PM +0200, Saku Ytti via cisco-nsp wrote:
> You might want add-path or best-external for predictability and
> improved convergence time.

Last time we did best-external with ASR9k it only worked in a useful
way if you are using labeled-unicast.  That was many years ago, so
it might have been fixed, but "test and expect surprises".

In our case, the effect was that the local router that exported
best-external to its peers was also installing the best-external
path into its local FIB, as a load-shared path(!).

So we had packets come in from uplink, the "good" path was "send
internal over our network", but half the packets got balanced 
via the "best-external" path.  Intereresting isseus ensued.

To me this never made sense but TAC claimed "this is the way it is,
we're not considering this a bug, use labeled-unicast, then it will
work fine".  As we didn't use LU, I could not verify this.

gert
-- 
"If was one thing all people took for granted, was conviction that if you 
 feed honest figures into a computer, honest figures come out. Never doubted 
 it myself till I met a computer with a sense of humor."
                             Robert A. Heinlein, The Moon is a Harsh Mistress

Gert Doering - Munich, Germany                             [email protected]

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