https://reference.opcfoundation.org/v104/Core/docs/Part4/5.6.2/
The documentation for the endpointUrl string states:

The network address that the Client used to access the Session Endpoint.
The HostName portion of the URL should be one of the HostNames for the application that are specified in the Server’s ApplicationInstanceCertificate (see 7.2). The Server shall raise an >AuditUrlMismatchEventType event if the URL does not match the Server’s HostNames. AuditUrlMismatchEventType event type is defined in OPC 10000-5.
The Server uses this information for diagnostics and to determine the set of EndpointDescriptions to return in the response.

Whereas the doc is clear about the necessity to raise a AuditUrlMismatchEventType, the doc is unclear on whether it is mandatory or not to specify a endpoint that strictly matches one of the exposed endpoint of the server.

Server can be addressed by hostname, fqdn , alias hostname and directly with IP address ...

For instance:

• Prosys Demo Server will reject the connection if the endpointUrl provided in the createSessionRequest doesn't exactly match the endpointUrl of one of the exposed endpoint of the server with a ServiceFault BadServiceUnsupported.

• UAAutomation CPPServer will accept the connection of the endpointUrl is opc.tcp://localhost:48010 our opc.tcp://192.122.122.14:48010 (with the server Ip address) or opc.tcp://HOSTNAME:48010 even though only opc.tcp://HOSTNAME:48010 appears in the endpoint descriptions.

Which behavior is correct ?

Also I am not sure that any CTT test verifies this aspect yet ...

If we decide that createSessionRequest must expose a known endpointUrl to the server. then we may have to provide the algorithm by which a client can reliably connect to the server if it only knows it IP address..:

• open a connection using on one of the possible hostnaame/ipaddress , create a secureChannel
• get the endpoints
• close connection
• find the exact end point matching the level of security required
  • open a new connection with the exact opc.tcp endpoint, create channel
• create session with this exact endpoint URL
  • activate session , etc ...