How to test RJ45 serial ports using a loopback plug

How to test RJ45 serial ports using a loopback plug

Each new unit that ships includes an accessory box which will contain one or two loopback plugs appropriate for the model's hardware:
  1. Yellow: Cisco pinout
  2. Red: Legacy pinout

These loopback plugs are helpful for determining if a serial port has failed or is experiencing errors.  It does this by routing output signals from the port to the appropriate input signal pins.  By using doing this test, you remove external factors like the settings, cabling, adapters, and target device to narrow down the possible cause of a serial port connection issue.  There are two tests which can be done:

Echo test:

This test will let you send a larger amount of data and can be done without affecting the other ports.
  1. Unplug any cabling currently connected to the port in question
  2. Plug in the appropriate loopback plug based on pinout
  3. Navigate to the Access tab
  4. Click the Console link for the port in question
  5. In the new tab, type any printable characters and monitor the output
    1. The expected result is to see the same characters echoed back on the screen.

Signal test:

This test will verify the signals are able to be sent and received in addition to passing normal data.
  1. Disable the serial port(s) to be tested in Device Manager
  2. Unplug any cabling currently connected to the port in question
  3. Plug in the appropriate loopback plug based on pinout
  4. Log into the admin CLI
  5. Access the root shell using: shell sudo su -
  6. Run the test using: nsc_hwtst.sh -s
    1. Note: Ports which do not have loopback plugs will show errors; this is normal.
    2. The expected result is that the port is question is not listed in the output.
  7. Re-enable the serial port(s) in Device Manager

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