# SANbox2-64 Port Loopback Tests

The port loopback test is a diagnostic tool that tests the functionality of one or more ports by sending a frame out through the loop, and then verifying that the frame received matches the frame that was sent. Only one port can be tested at a time for each type of test. You can use the default set of test parameters or you can configure your own test parameters.

The three types of SANbox2-64 port loopback tests are:

* Internal (SerDes level) - The Internal test verifies port circuitry. The SerDes level test sends a test frame from the ASIC through the SerDes chip and back to the ASIC for the selected ports. The port passes the test if the frame that was sent by the ASIC matches the frame that was received.

* External (SFP level) - The External test also verifies port circuitry. The SFP level test sends a test frame from the ASIC through the SerDes chip, through the SFP transceiver fitted with a loopback plug, and back to the ASIC for the selected ports. The port passes the test if the test frame that was sent by the ASIC matches the test frame that was received.

* Online (node-to-node) - The online test verifies communications between the port and its device node or device loop. The port being tested must be online and connected to a remote device.