Serial interfaces cables and converters scheme
Used to verify the port is functional.

CheckIt/Norton/Passmark Loopback 

Name Pin Pin
Jumpering 1 2 3
Jumpering 2 4 5
Jumpering 3 6 8,20
Jumpering 4 15 17,24

Loopback, or loop-back, refers to the routing of electronic signals, digital data streams, or flows of items back to their source without intentional processing or modification. This is primarily a means of testing the transmission or transportation infrastructure. A communications transceiver can use loopback for testing its functionality. For example, a device transmit pin connected to its receive pin will result in the device receiving exactly what it transmits. Moving this looping connection to the remote end of a cable adds the cable to this test.

25 pin D-SUB female connector layout
25 pin D-SUB female connector
at the computer
25 pin D-SUB male connector layout
25 pin D-SUB male connector
at the loopback
According to 3 reports in our database (3 positive and 0 negative) this pinout should be correct.

Is this pinout
Serial port Loopback (25 pin) visual pinout:
Serial port Loopback (25 pin) diagram
click to enlarge
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