BadCommunicationError when trying to connect to Siemens PLC

[RichG]

Hello

We are working on a project for a customer using Siemens OPCUA-enabled PLCs, which have an integrated OPCUA server. We are using UAExpert version 1.4.4 275 as an OPCUA client for testing of the system.

The customer has stated that the Siemens OPCUA server on the PLC should use a server certificate supplied by them, but whenever the PLC uses this certificate, UAExpert fails to connect with a 'BadCommunicationError' message. The PLC can be pinged and is on the same network. If we use the PLC's own self-signed server certifcate, UAExpert connects straight away and everything works.

Obviously this points to an issue with the customer certificate used on the server (PLC), but to help us work out the exact issue, in this situation what would the 'BadCommunicationError' indicate? Does it provide any idea of why the server certificate seems to cause this communication failure? Is there any further detailed diagnosis we can enable in UAExpert to see more informatoin on the connection attempt and failure, or is this just a general error when for whatever reason, UAExpert cannot access the server.

Thanks.

Rich.

[Support Team]

Hello RichG,

the error code BadCommunicationError most possibly results from the OPC UA server not starting up at all on the PLC. When replacing the certificate on the PLC, did you also replace the private key? If you didn't do that, the server won't start as certificate and private key have to match.

If that's not the case, please check with the PLC vendor on how to enable the OPC UA server trace on the PLC, which will most likely contain more detailed information about the reason for the error.