With three config servers set up it is possible to have a scenario when due to incorrect host names resolution connections to the config servers established incorrectly. For example, mongos, instead of connecting to the config servers #1, #2 and #3 may have two connections to the config server #1, none to #2 and one to #3.

Currently mongos is unable to figure out that something is wrong, despite that any metadata modifications result in a duplicate key exception.

There should be a way for mongos to ensure it is not connected twice to the same config server.