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Table 1 Actions to take upon detection of a loop condition
Port type
Actions
No
rotective action is confi
ured
A
rotective action is confi
ured
Access port
• Place the receiving interface in controlled
mode. The interface discards all incoming
packets, but still forwards outgoing packets.
• Generate traps and log messages.
• Delete all MAC address entries of the
interface.
• Perform the configured protective
action.
• Generate traps and log messages.
• Delete all MAC address entries of the
interface.
Hybrid or trunk
port
• Generate traps and log messages.
• If loopback detection control is enabled,
place the receiving interface in controlled
mode. The interface discards all incoming
packets, but still forwards outgoing packets.
• Delete all MAC address entries of the
interface.
• Generate traps and log messages.
• If loopback detection control is
enabled, take the configured
protective action on the interface.
• Delete all MAC address entries of the
interface.
Configuration restrictions and guidelines
• To use loopback detection on an Ethernet interface, you must enable the function both globally and
on the interface.
• To disable loopback detection on all interfaces, run the undo loopback-detection enable command
in system view.
• To enable a hybrid or trunk port to take the administratively specified protective action, you must use
the loopback-detection control enable command on the port.
• When you change the link type of an Ethernet interface by using the port link-type command, the
switch removes the protective action configured on the interface. For more information about the
port link-type command, see Layer 2—LAN Switching Command Reference.
Configuration procedure
To configure loopback detection:
Ste
Command
Remarks
1. Enter system view.
system-view N/A
2. Enable global loopback
detection.
loopback-detection enable
By default, global loopback
detection is disabled.
3. Enable multi-port loopback
detection.
loopback-detection
multi-port-mode enable
Optional.
By default, multi-port loopback
detection is disabled, and the
device can only detect single-port
loopback.
4. Set the loopback detection
interval.
loopback-detection interval-time
time
Optional.
The default setting is 30 seconds.
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