Multihomed route visibility

Mon Nov 4 16:15:59 UTC 2019

On Mon, Nov 4, 2019 at 8:13 AM Boyle, Patrick via NANOG <nanog at nanog.org>
wrote:

> We are advertising the same prefix to ISP A & ISP B. When looking at
> various route servers across the world, I always see the path through ISP A
> in the BGP table, but most don’t show a path at all through ISP B (some do,
> like Oregon IX). I would expect any router with the full table to show both
> routes. Is this a consequence of how the route servers are peered up? Are
> they only displaying the preferred path? ISP Issue? Am I missing something?
>

Hi Patrick,

Routers only propagate the *best* BGP route for the target network. You'll
see both only where the AS received different best routes from its peers.

Regards,
Bill Herrin

-- 
William Herrin
bill at herrin.us
https://bill.herrin.us/
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