MyFileName.config.xml is preferred, but functionally, it just needs to be any name that matches the <FilePath> element in the <UAClientEngine> <ConfigurationLocation> in the main config file.

Hello.

1. We are using QuickOPC version 2021.2 (5.61.241.1). Is it OK?

Yes.

2. See the attached config file of our application. Is it OK?

No. The <configSections> part (Point 1 in kb.opclabs.com/OPC_UA_.NET_SDK_Configuration ) is missing.
And, not sure if the positioning is relevant, but I suggest that you place any new stuff just above the final </configuration> closing tag.

3. Where should I place the UAClientEngine.Config_2021-07-05.xml file (after I change the <MaxBufferSize> from 65535 to 65536)?

In the same folder as the program's EXE and its .config file.

3.1. What should be the file name?

It does not matter. It just needs to match the name in the <filePath> element (Point 2 in kb.opclabs.com/OPC_UA_.NET_SDK_Configuration ).

3.2. Is it in the same folder where application exe file is?

Yes

3.3. Should we specify the file name of the above file in our config file (<FilePath>MyApplication.Config.xml</FilePath>)

Yes

The workaround is to create and activate a custom OPC UA .NET SDK Configuration, as described here: kb.opclabs.com/OPC_UA_.NET_SDK_Configuration , and in it, change the value under -> from 65535 to 65536. Note that two XML files are involved - one is the standard .NET configuration file for the .EXE that needs to be changed to name the new section; the other is the .NET SDK configuration file which you are probably not deploying yet, so it is a "new" one.

The (yet unchanged) internal SDK configuration file from QuickOPC 2021.2 is attached.

Best regards

File Attachment:

File Name: UAClientEn...7-05.xml
File Size:12 KB

Hello,
regarding the error "Message size 65536 bytes is too large for buffer of size 65535":

This is a bug in KEPServerEX. It negotiates a message size and then it violates the agreement by sending a larger message. I was able to prove it with KEPServerEX V6.1.655.0, and it works fine with their current version, which is V6.10.623.0. I then searched the Kepware release notes, and it is listed there: On www.kepware.com/en-us/support/release-notes/ , select Product = KEPServerEX and Version = 6.4.321.0 . It has this text under the Release notes:

OPC UA Server Interface
Resolved an issue where the server could send packets that exceeded the ReceiveBufferSize negotiated with the client in the OPC UA TCP Hello message.

(It does not happen with UaExpert because they happened to choose a buffer size that does not trigger the KEPServerEX bug.)
The best and proper resolution is thus to upgrade to latest KEPServerEX version, or at least V6.4.321.0.

If you could not upgrade the KEPServerEX, then there are ways to work around the problem which I can advise. In addition in QuickOPC 2021.3, we will add some mitigations too. There will be no change to QuickOPC 2021.2, because there is no bug to fix - the problem is on the server side.

Best regards

Thank you. I was able to reproduce the problem now. It appears that it only happens when encrypted OPC UA connection is in use.

I will investigate and let you know here when I have more information.

Best regards