1-7z To enable loopback detection on a specific port, you must use the loopback-detection enablecommand in both system view and the specific port view.z After you use the undo loopback-detection enable command in system view, loopback detectionwill be disabled on all ports.Enabling Loopback TestYou can configure the Ethernet port to run loopback test to check if it operates normally. The portrunning loopback test cannot forward data packets normally. The loopback test terminatesautomatically after a specific period.Table 1-7 Enable loopback testOperation Command RemarksEnter system view system-view —Enter Ethernet port view interface interface-type interface-number —Enable loopback test loopback { external | internal } Optionalz external: Performs external loop test. In the external loop test, self-loop headers must be used onthe port of the switch ( for 100M port, the self-loop headers are made from four cores of the 8-corecables, for 1000M port, the self-loop header are made from eight cores of the 8-core cables, thenthe packets forwarded by the port will be received by itself.). The external loop test can locate thehardware failures on the port.z internal: Performs internal loop test. In the internal loop test, self loop is established in theswitching chip to locate the chip failure which is related to the port.Note that:z After you use the shutdown command on a port, the port cannot run loopback test.z You cannot use the speed, duplex, mdi and shutdown commands on the ports running loopbacktest.z Some ports do not support loopback test, and corresponding prompts will be given when youperform loopback test on them.Enabling the System to Test Connected CableYou can enable the system to test the cable connected to a specific port. The test result will be returnedin five seconds. The system can test these attributes of the cable: Receive and transmit directions (RXand TX), short circuit/open circuit or not, the length of the faulty cable.
