AS PATH limits

Jakob Heitz (jheitz) jheitz at
Thu Sep 21 18:51:04 UTC 2017

The consequence of keeping a route with a long AS_PATH is that it uses a little more memory.
Also, if you send it on, you will add one ASN and may exceed the maximum BGP message size and not be able to send it.
Even that is no reason to drop the incoming route.
The consequence of dropping the route is that someone loses connectivity because you dropped it.

The need for limiting AS_PATH length stemmed from this incident:

This bug has long been fixed, so it should not happen again.
However, if you want to be extra cautious, because unpatched routers may still be out there,
then 200 should not drop any normal route. Just keep an eye on what you are dropping


Date: Tue, 19 Sep 2017 13:33:03 +0000
From: craig washington <craigwashington01 at>
To: "nanog at" <nanog at>
Subject: AS PATH limits
	<SN1PR0701MB206268455259CC64FC0D8ED7A8600 at>
Content-Type: text/plain; charset="iso-8859-1"

Hello world.

I was wondering and forgive me if this discussions has already taken place.

How many AS PATHS are too many?

Meaning how do we determine how many to filter on transit links or public peering links?

Thanks in advance

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