12
when a loop is detected, for example, to shut down the interface. Depending on whether a protective
action is configured, the switch takes the actions in
to alleviate the impact of the loop condition.
Table 1
Actions to take upon detection of a loop condition
Port type
Actions
No protective action is configured
A protective action is configured
Access port
•
Place the receiving interface in controlled mode.
The interface drops the incoming packets and
correctly sends 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 does not receive or send 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.
•
When the multi-port loopback detection function is enabled, the function can also detect single-port
loops.
•
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:
Step Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enable global
loopback detection.
loopback-detection enable
Disabled by default.
3.
Enable multi-port
loopback detection.
loopback-detection
multi-port-mode enable
Optional.
By default, multi-port loopback detection is
disabled, and the switch can only detect
single-port loopback.
4.
Set the loopback
detection interval.
loopback-detection interval-time
time
Optional.
30 seconds by default.
