Digi CM - Manual (Page 108)

Configuring Port Clustering
108 Chapter 13
8. Enter the Base source port number to start the numbering and click Set .
9. Enter the Base destination port number and click Set .
Note: The Source ports and Destination ports can be understood as the Destination port
number is the actual physical port number on the Slave unit and the Source port
number is the extension number of the Slave unit to the Master unit. In other
words, the Master device port number 7051 = Slave port device number 7001.
10. Click Save & apply .