Loopback-Detection Enable - 3Com 5500-EI PWR Reference Manual

loopback-detection enable

Syntax
loopback-detection enable
undo loopback-detection enable
View
System view or Ethernet port view
Parameters
None
Description
Use the loopback-detection enable command to enable the loopback detection feature on ports to
detect whether external loopback occurs on a port.
Use the undo loopback-detection enable command to disable the loopback detection feature on port.
1) If a loop is found on an access port, the system sets the port to the block state (where the port
cannot forward data packets), sends log messages to the terminal, and removes the corresponding
MAC forwarding entry.
If you have also enabled the loopback port auto-shutdown function on the port, the system shuts
down the port, and sends log messages to the terminal. After the loop is removed, you need to use
the undo shutdown command to bring up the port.
If you have not enabled the loopback port auto-shutdown function on the port, the port
automatically resumes the normal forwarding state after the loop is removed.
2) If a loop is found on a trunk or hybrid port, the system merely sends log messages to the terminal
but does not set the port to the block state or remove the corresponding MAC forwarding entry.
You can also further control the loopback port by enabling one of the following function on it (note
that, the following two functions are mutually exclusive, and the latest function configured takes
effect):
Enable the loopback port control function on the port: the system sets the port to the block state
(where the port cannot forward data packets), sends log messages to the terminal, and removes
the corresponding MAC forwarding entry. After the loop is removed, the port automatically resumes
the normal forwarding state.
Enable the loopback port auto-shutdown function on the port: the system shuts down the port and
sends log messages to the terminal. After the loop is removed, the port does not automatically
resume the normal forwarding state. Instead, you need to use the undo shutdown command to
bring up the port.
The loopback detection function on a specific port can take effect only after you enable the loopback
detection function globally (in system view) and on the port (in the specified port view).
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