vektor

They don't do any NAT traversal, but that use UPnP to open ports. During a talk Gunnar Kreitz said that they still got a 60% success rate for connections (if I remember correct, varied between countries also). And that this was good enough for them. More can be read in this paper: http://www.csc.kth.se/~gkreitz/spotify-p2p11/spotify-p2p11.p...

If this is a problem or not depends on what you mean. If a port for some strange reason goes up and down 100 times a sec then this will cause 100 "port status" messages to be sent to the controller. This might be a problem, but the controller should be able to handle this, it's still a small amount of traffic and should not require that much processing. There is also some distributed controllers, for example Onix. If you talk about convergence of the network topology i general then it depend largely on the controllers implementation.