1 | initial version |
The Mongo dissector registers to dissect traffic on tcp port 27017, but has a preference setting to modify that if required. As you have found out you can also use "Decode As ..." to force a temporary override of the port. There is no heuristic port detection for the mongo dissector.
Presumably the mongo traffic you are capturing is NOT running on the default mongo port of 27017, or you have changed the mongo dissector port preference.