I have worked on more than one BGP implementation, but not all of them, of course. On memory requirements for as-paths: Attribute sets are shared among stored routes. That means if two stored routes have the same attribute sets, the attribute set is stored only once. As-paths are shared among attribute sets. That means if two stored attribute sets have the same as-path, then the as-path is stored only once. Storing them in the control plane is not a big problem.
However, as-paths can be sent in netflow. Netflow is generated in the forwarding plane. AS-paths are not stored in expensive fast memory on the forwarding plane, but still, using memory on the forwarding plane has greater impact than on the control plane. An as-path consists of AS_SEQUENCEs (and other elements). An AS_SEQUENCE can contain a maximum of 255 ASNs. If the as-path is longer, then multiple AS_SEQUENCEs are required. The code to parse them and create them is not often exercised and is a potential for bugs in fresh code. The older implementations have these bugs well and truly shaken out of them. Regards, Jakob. From: GROW <[email protected]> On Behalf Of Michael McBride Sent: Sunday, July 26, 2020 11:42 AM To: [email protected] Subject: [GROW] AS_Path prepend BCP Hello wg, We have submitted https://datatracker.ietf.org/doc/draft-mcbride-grow-as-path-prepend/ which is intended to be a bcp in the use of AS_Path prepend based on work of Doug Madory. As we state in the intro: AS_Path prepending is discussed in Use of BGP Large Communities [RFC8195] and this document provides additional, and specific, guidance to operators on how to be a good internet citizen with the proper use of AS_Path prepend. We would encourage feedback on this document. thanks, mike
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