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z To enable loopback detection on a specific port, you must use the loopback-detection enable
command in both system view and the specific port view.
z After you use the undo loopback-detection enable command in system view, loopback detection
will be disabled on all ports.
Enabling Loopback Test
You can configure the Ethernet port to run loopback test to check if it operates normally. The port
running loopback test cannot forward data packets normally. The loopback test terminates
automatically after a specific period.
Follow these steps to enable loopback test:
To do... Use the command... Remarks
Enter system view
system-view
—
Enter Ethernet port view
interface interface-type interface-number
—
Enable loopback test
loopback { external | internal } Required
z external: Performs external loop test. In the external loop test, self-loop headers must be used on
the port of the switch ( for 100M port, the self-loop headers are made from four cores of the 8-core
cables, for 1000M port, the self-loop header are made from eight cores of the 8-core cables, then
the packets forwarded by the port will be received by itself.). The external loop test can locate the
hardware failures on the port.
z internal: Performs internal loop test. In the internal loop test, self loop is established in the
switching 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 loopback
test.
z Some ports do not support loopback test, and corresponding prompts will be given when you
perform loopback test on them.
Enabling the System to Test Connected Cable
You can enable the system to test the cable connected to a specific port. The test result will be returned
in five seconds. The system can test these attributes of the cable: Receive and transmit directions (RX
and TX), short circuit/open circuit or not, the length of the faulty cable.
Follow these steps to enable the system to test connected cables: