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Subject: Re: [mqtt] MQTT 3.1.1 partial connect packets over TCP

Hi Alex
The fact that it's in the variable header doesn't make it optional... the 'MQTT' "eye catcher" is there for exactly that purpose of differentiating protocols in a multi-protocol server (and for helping a server know that the client that's connected is not talking MQTT).

So if a client library doesn't send all the elements that are specified in the Variable Header section of the spec, then it's malformed...

Maybe there should be some more "MUST"s in the spec??


Andy Stanford-Clark
Distinguished Engineer, Internet of Things

Master Inventor, Member IBM Academy of Technology, Fellow BCS
Honorary Professor University of East Anglia, Visiting Professor University of Newcastle, Adjunct Professor University of Southampton.
Tel: +44 (0)7801 787096 [internal: 37 277624]   twitter: @andysc

From:        "Kritikos, Alex" <Alex.Kritikos@softwareag.com>
To:        "mqtt@lists.oasis-open.org" <mqtt@lists.oasis-open.org>
Date:        17/05/2017 11:52
Subject:        [mqtt] MQTT 3.1.1 partial connect packets over TCP
Sent by:        <mqtt@lists.oasis-open.org>

Hello everyone,
Apologies if this has been answered before but I could not find a definitive answer so far.
When using a TCP transport, is a client library sending a partial connect packet (2 byte fixed header only) while connecting to an MQTT broker conforming to the specification?
I understand that it may not be a problem for an MQTT only broker but what about multi protocol brokers, packet inspectors, load balancers? The specification only has a non normative comment on line 395:
Packet inspectors, such as firewalls, could use the Protocol Name to identify MQTT traffic.
In the above case though, the protocol name is not sent as it resides in the variable header of the packet.
Any assistance would be greatly appreciated.
Alex Kritikos

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