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<p>Hello,</p>
<p>you basically want one router to prepend two ASNs for one hop, if I
understand correctly. That’s not an intuitive / default-worthy
behavior.</p>
<p>On Thu, Oct 10, 2024 at 10:20:51AM +0000, Ochalski, Radoslaw via
Bird-users wrote:</p>
<blockquote>
<p>Here you have same route exported via Juniper border, local ASN 20940
is prepended by default:</p>
<p>inet.0: 955317 destinations, 2138917 routes (950415 active, 218793
holddown, 14419 hidden) Prefix Nexthop MED Lclpref AS path *
20.135.0.0/16 Self 20940 8075 I</p>
<p>vs bird:</p>
<pre><code> BGP.as_path: 8075</code></pre>
<p>[truncated]</p>
</blockquote>
<p>BIRD shows the route after filters but <em>before</em> BGP applies
the export modifications, which includes prepending the local AS to the
AS path iff the session is EBGP. I expect that Juniper is showing the
route as-it-goes-to-the-wire.</p>
<p>BIRD 2 doesn’t allow showing routes that way; this is possible in
BIRD 3 with <code>export table on</code> by showing routes from the
export table.</p>
<p>If you capture tcpdump from BIRD, you’ll see the AS prepended.</p>
<p>Maria</p>
<p>–<br />
Maria Matejka (she/her) | BIRD Team Leader | CZ.NIC, z.s.p.o.</p>
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