[ixpmanager] IXP Manager Route Server Behaviors

[Richard Laager]

This is mostly for Barry when reviewing the Route Server templates (not 
sure whether that happened in Q4 as planned). Given Nick Hilliard is an 
author RFC 7947 & 7948, surely these are on your radar. But I wanted to 
specifically ask about / mention the following specific items.

RFC 7947, 2.3.2.2.2 discusses BGP ADD-PATH. This is what I was looking 
into which lead me here. I am looking at adding "add paths tx;" to the 
route server template. However, this thread about a potential BIRD bug 
gives me pause:
https://bird.network.cz/pipermail/bird-users/2024-January/017296.html

RFC 7947 contemplates ADD-PATH as an alternative to 2.3.2.1 "Multiple 
Route Server RIBs" which is what IXP Manager's templates are already doing.

However, if the IXP participant is filtering on receive, ADD-PATH can 
still provide value. That is, if the participant would filter out the 
best path (from the route server's perspective) but would not filter out 
an alternate path, then ADD-PATH would allow that participant to use 
that alternate path.

My reasoning about ADD-PATH largely assumes that receive-side filtering 
could not be moved to the route server. I was also given this link (see 
"IRRDB based Filtering"):
https://www.ams-ix.net/ams/documentation/ams-ix-route-servers

They have apparently implemented a script that honors:
https://www.ietf.org/archive/id/draft-ietf-grow-rpsl-via-01.txt

That would be a lot more work to implement. Does anyone here know AMS-IX 
people? Would they be willing to share their script?

----

While reading RFC 7947 for the above thing, I found this:

RFC 7947, 2.2.3 says to preserve the MULTI_EXIT_DISC. Is BIRD doing that 
(with the IXP Manager template config)?

This thread seems to suggest it is not:
https://bird.network.cz/pipermail/bird-users/2020-December/015070.html

unless you specifically put "bgp_med = bgp_med;" in an export filter:
https://bird.network.cz/pipermail/bird-users/2020-December/015075.html

-- 
Richard