Dear Jörg, On Thu, Aug 31, 2017 at 12:50:58PM +0200, Jörg Kost wrote:
but isn't peer A prefix-out a synonym for peer B prefix-in, that will lead to the same result, e.g. a BGP teardown?
I just feel that this will add another factor, that people will not use or abuse: neigh $x max-out infinite
I feel you may be overlooking a key aspect here: Currently all of us rely on our peer's 'inbound maximum prefix limit', and obviously these are not always set correctly. An 'outbound maximum prefix limit' offers networks that care about the rest of the world the option to 'self-destruct' the EBGP session in order to protect others. An 'outbound maximum prefix limit' is a 'permissionless' feature in that you do not require cooperation or support from your peering partner at the other end of the sessio in order to deploy the 'self-destruct to protect' mechanism. If you don't want to use it, then don't. If people configure "neighbor $x max-out infinite" that is fine by me, at least they made a conscience choice, it is no worse than today, and it is clearly documented in the running-configuration what the ramifications of the EBGP session could be.
What about adding an option to the BGP session that A & B do agree on a fixed number of prefixes in both directions, so Bs prefix-in could be As prefix-out automatically?
I prefer unilateral permissionless mechanisms. Adding new negotiable options to BGP sessions is a lot of work and requires both parties to run software that supports the new feature, whatever it is. Anything that can be done without requiring your peer's cooperation will be more robust. Kind regards, Job