Thank you, Nick. Your answers are helpful for the ASPA-based AS path verification specification for keeping it simple in this regard.
>I've not come across any situation where the two relationships happen on the >same bgp session. Great to know that. Sriram ================ -----Original Message----- From: Nick Hilliard <[email protected]> Sent: Sunday, April 21, 2024 1:10 PM To: Sriram, Kotikalapudi (Fed) <[email protected]> Cc: [email protected]; [email protected] Subject: Re: [GROW] Question about mutual transit and complex BGP peering Sriram, Kotikalapudi (Fed) wrote on 21/04/2024 16:53: > Q1: Consider an AS peering relationship that is complex (or hybrid) > meaning, for example, provider-to-customer (P2C) for one set of > prefixes and lateral peers (i.e., transit-free peer-to-peer (P2P)) for > another set of prefixes. Are these diverse relationships usually > segregated, i.e., P2C on one BGP session and P2P on another? How > often they might co-exist within one single BGP session? this sort of relationship is common but unintentional. You see it at IXPs where P provides transit to C over a normal transit link, but they unintentionally also peer via a route server. Oops. Incidentally, this is one of the reasons why it's critically important for route servers to provide prefix filtering knobs and why mandatory interconnection (which thankfully only happens in a tiny handful of IXPs) is such a bad idea. P2P+P2C interconnection can also happen intentionally, but this is a corner case - most transit providers don't like doing this, not least for the simple reason that it moves traffic from the paid link to a lower- or zero-revenue link. I've not come across any situation where the two relationships happen on the same bgp session. > Q2: Consider an AS peering relationship that is mutual transit (i.e., > P2C relationship in each direction for all prefixes). Is this > supported within one single BGP session? How often the ASes might > setup two separate BGP sessions between them -- one for P2C in one > direction (AS A to AS B) and the other for P2C in the opposite > direction (AS B to AS A)? This would probably be done with a single BGP session. Mutual transit is not widely used in developed interconnection markets. Nick _______________________________________________ GROW mailing list [email protected] https://www.ietf.org/mailman/listinfo/grow
