Routing triangle inequality

Despite the years of internet development (or maybe due to it?), the routing problems are still prevalent. In fact, it is quite hard to have a consistent routing behavior. One of the user-visible failures is a "triangle inequality". In triangle inequality, we have three servers A,B,C. A is able to communicate with B and B is able to communicate with C, nevertheless servers A and C are not able to communicate.

You may guess why I am writing this post -- exactly because I encountered such a problem today. And not only once. There seems to be a bunch of sites (dsl.sk, sportujes.sk, websupport.sk, etc.) down here in Switzerland although they are working from Slovakia. The reason is probably some misconfiguration on the way between switch.ch (swiss academic network) and www.six.sk (slovak peering center). Whatever the reason, the results are clear - unhappy customers and a lot of research to do on reliable internet routing protocols!