cold-potato vs. hot-potato routing
expressioncloudISP & telecom
Two philosophies for carrying traffic: hot-potato hands it to the next network as soon as possible; cold-potato keeps it on your backbone as long as possible.
Clouds sell cold-potato as 'premium tier': more of the journey on their fiber, less on the open internet.
Hot potato routing hands traffic to the destination network as soon as possible, at the nearest exchange point, so the sending network carries it the shortest distance. Cold potato routing carries traffic on your own backbone as far as possible before handing it over.
The choice is economic before it is technical. Hot potato minimizes your transit costs and pushes the carrying cost onto the receiving network, which is the default for most peering relationships. Cold potato costs the sender more and is what a content provider chooses when it wants control over quality: keeping traffic on your own well-managed network until it is close to the user means fewer variables and better measured performance.
It explains asymmetric routing, which is one of the more confusing things to diagnose. If both networks apply hot potato, traffic from A to B leaves at one exchange and the return traffic leaves at a completely different one, so the two directions take physically different paths with different latency and different failure modes. Anyone troubleshooting a one-way problem is usually looking at this, and looking only at the outbound path will not find it.