Thanks for the quick answers!
What should I set rtt-cost/max-rtt-penalty to?
Max-rtt-penalty controls how much Babel will prefer routes with many links but low RTT to routes with few links but hight RTT. The default is fairly conservative, meaning that RTT has only a very small influence on routing. You should set it to 96*n where n is the maximum number of extra links that you're willing to take in order to avoid one high-RTT link. You should probably set it to 400 or so, and start tweaking from there. The value used by Nexedi (5000) looks quite extreme to me. As to rtt-decay, the default value should be fine unless you have a mobile network. Increase it in order to react faster to RTT variations, at the risk of route flaps every time the network has a hiccup. -- Juliusz