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Connection establishment

Questions regarding the use of the UaExpert.

Connection establishment

Postby datenRaten » 16 Oct 2019, 10:43


I got a question regarding the connection establishment using UaExpert.
Tools used: UaExpert v1.5.1, OPC UA C++ Demo Server V1.7.0

When following the connection establishment process using wireshark, two phases can be observed.
First the sequence is: Hello -> Ack -> OpenSecureChannelRequest -> OpenSecureChannelResponse -> GetEndpointsRequest -> GetEndpointsResponse -> CloseSecureChannelRequest

Shortly after the "real" connection is established:
Hello -> Ack -> OpenSecureChannelRequest -> OpenSecureChannelResponse -> CreateSessionRequest -> CreateSessionResponse -> ActivateSessionRequest -> ActivateSessionResponse

Is this expected behaviour? The specification and other traces are telling me that the process can be done in a single step. Is there a special reason it is done this way by UaExpert?

background: The aim is to classify traffic (especially OPC UA) using a statistical approach. For that simulations of the connection establishment and data exchange are necessary and I'm not sure whether the case presented here should be considered.
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Re: Connection establishment

Postby Support Team » 08 Jan 2020, 19:07


the "double" connection is the intended behaviour. A Client will typically discover the available endpoints in a first step and in a second step connect for the "real". A good client will even check if for both connection approach the server returned the same security relevant data.
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