H3C Technologies H3C S12500 Series Switches - Manual (Page 203)

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The output shows that no loop is detected on GigabitEthernet 4/0/1 and GigabitEthernet 4/0/2. The
reason is that the loopback detection action is set to shutdown, in which case, the two ports are
automatically shut down when a loop occurs on them. The shutdown action removes the loop. Use the
display interface command to display the status information of GigabitEthernet 4/0/1 and
GigabitEthernet 4/0/2 on Device A:
# Display the status information of GigabitEthernet 4/0/1 on Device A.
[DeviceA] display interface gigabitethernet 4/0/1
GigabitEthernet 4/0/1 current state: DOWN ( Loopback detection-protected )
...
# Display the status information of GigabitEthernet 4/0/2 on Device A.
[DeviceA] display interface gigabitethernet 4/0/2
GigabitEthernet 4/0/2 current state: DOWN ( Loopback detection-protected )
...
The output above shows that GigabitEthernet 4/0/1 and GigabitEthernet 4/0/2 have already been
shut down by the loopback detection module.