Upstream-servers order/selection/logic?!

If not specifying "all-servers" I would like it to use the upstream-servers in the exact order as specified in the config-file. If the first upstream goes down it should use nr 2 in the list, but test periodically if nr 1 is back up and running again and then switch back. If all upstream-servers fails, it should use the fallback-servers with the same principle and using nr 1.

Now it seems to pick a random server and stick with that.