Post by Kai ChenThere is the model where all partcipants peer through agency of 3rd party.
That tends to be looked on as an extremely bad idea, but some regulatory
environments encourage or enforce that sort of behavior particularly around
the monopoly PTT.
I don't know if the 3rd party you mentioned is the IXP?
Some IXPs have MLPA (MultiLateral Peering Agreements) where some or all
of the participants agree to connect to a route server (usually with
it's own AS) and exchange routes this way.
It's reasonably common around AsiaPac - all the peering fabrics in
Australia are MLPA for example, but I can think of optional examples in
the USA (eg. Any2) that have it as an option or places like HKIX which
have an MPLA which is mandatory for Hong Kong prefixes.
This doesn't stop you doing bilateral as well across the same fabrics.
MLPA works well in certain environments, especially where the major IP
transit providers in a country won't peer, but rivalries tend to mean
that a neutral (or fairly neutral) 3rd party can provide the routing
part (this is pretty much what happened in Australia). It's
convienient for content providers - they can "hook up" to one route
server and often pickup half of the people on the exchange without
having to spend ages negotiating with small networks who often don't
have the technical know how or don't have the BGP experience, or indeed
the smaller networks themselves as they can connect to an exchange and
at least guarantee enough data to justify doing so.
It gets more complex as some networks then become bigger and become
transit providers and don't like customers sending routes to them via a
peering fabric etc. Which is why, with a much more diverse range of
networks and no one player dominating people the transit game (eg. in
the USA, Western Europe) that MLPA isn't common.
Some MLPAs give you some control over routing (eg. don't send my
prefixes to ASxxxx), but a lot don't.
Regards,
Matthew