Re: [Sidrops] ASPA false leak

Randy Bush <randy@psg.com> Wed, 16 October 2019 01:45 UTC

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Date: Wed, 16 Oct 2019 03:45:44 +0200
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From: Randy Bush <randy@psg.com>
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Subject: Re: [Sidrops] ASPA false leak
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> Consider the topology:
> 
>    AS5      AS3
>      \     /   \
>       \   /     \
>        AS4     AS2
>          \     /
>           \   /
>            AS1
> 
> AS1 has providers AS2 and AS4.
> AS2 has provider  AS3.
> AS4 has providers AS3 and AS5.
> 
> AS5 receives a route with AS-path (4 3 2 1).
> ASPA would declare that AS4 leaked the route from AS3 to AS5.
> However, AS4 is an authorized provider for AS1.
> Even though AS4 has a path to AS1, it chose to use an alternative
> valid path to reach AS1.

and that alternate path sure looks a lot like a route leak.

randy