Managing Physical Interfaces Loopback Detection Configuration
Configuration Guide  
  95
Step 3 loopback-detection interval 
interval-time
Set the interval of sending loopback detection packets which is used to detect the loops in 
the network.
interval-time: 
The interval of sending loopback detection packets. The valid values are from 
1 to 1000 seconds. By default, the value is 30 seconds.
Step 4 loopback-detection recovery-time
 recovery-time
Set the recovery time, after which the blocked port in Auto Recovery mode can 
automatically recover to normal status.
recovery-time
: It is integral times of detection interval, ranging from 1 to 100. The default 
value is 3.
Step 5 interface {
 
fastEthernet 
port
 | range fastEthernet 
port-list 
| gigabitEthernet
 port
 | range
 
gigabitEthernet
 port-list
 }
Enter interface configuration mode.
Step 6 loopback-detection
Enable loopback detection of the port. By default, it is disabled.
Step 7 loopback-detection config process-mode { alert | port-based } recovery-mode { auto | 
manual }
Set the process mode when a loopback is detected on the port. There are two modes:
alert: When a loop is detected, the switch will send a trap message and generate an entry on 
the log file. It is the default setting.
port-based: When a loop is detected, the switch will send a trap message and generate an 
entry on the log file. In addition, the switch will totally block the port on which the loop is 
detected and no packets can pass through the port.
Set the recovery mode for the blocked port. There are two modes:
auto: After the recovery time, the blocked port will automatically recover to normal status 
and restart to detect loops in the network.
manual: The blocked port can only be released manually. You can use the command 
loopback-detection recover under interface configuration mode to recover the blocked 
port to normal status.
Step 9 show loopback-detection global
Verify the global configuration of Loopback Detection.
Step 10 show loopback-detection interface  {
 
fastEthernet 
port 
| gigabitEthernet
 port
 }
Verify the Loopback Detection configuration of the specified port.
Step 11 end
Return to privileged EXEC mode.
Step 12 copy running-config startup-config
Save the settings in the configuration file.
The following example shows how to enable loopback detection globally (keeping the 
default parameters):
Switch#configure