Can mqtt v5 client connect to mqtt v3.1.1 broker?

Question

I want to use mqtt v5 client, but the service I am working with has only mqtt v3.1.1 broker. Would I be able to use mqtt v5 client?

Answer 1

This will be specific to the client. The readme is not clear, but most clients support both v3.1 and v5.

You will have ask the libraries maintainer for clarification, but looking at the code it has hard coded protocol version flags in the connect packet, so it looks like it will only work with a MQTT v5 broker.

https://github.com/quartiq/minimq/blob/cff0f57567224de9a646320c17dcca73035d248a/src/packets.rs#L57

A v5 only client will not connect to a v3.1 broker.