When ITP/Server is installed, it is configured with 2 default TCP/IP ports: one port for the internal communication between the ITP/DP Manager and the Document Processors (the so-called internal interface) and one port to submit the requests to (the so-called external interface). A second ITP/Server will be installed with the same default ports. To avoid problems, this second ITP/Server needs to be reconfigured:
The port for the internal interface can be configured on the Servers tab of the Server node.

Default, this port is set to 3000. Just select another (available) port.
The port for the external interface can be configured on the DP Manager tab of the installed ITP/Server:

Default, this port is set to 3001. Just select another (available) port.