1-6
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 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:
To do... Use the command... Remarks
Enter system view
system-view
—
Enter Ethernet port view
interface interface-type
interface-number
—
Enable the system to test
connected cables
virtual-cable-test
Required
z Optical port (including Combo optical port) does not support VCT (virtual-cable-test) function.
z Combo electrical port supports VCT function only when it is in UP condition (using undo shutdown
command), normal Ethernet electrical port always supports this function.
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