C
HAPTER
 31
  |  Loopback Detection Commands
–  1048  –
loopback-detection This command enables loopback detection globally on the switch or on a 
specified interface. Use the no form to disable loopback detection.
SYNTAX 
[no] loopback-detection
DEFAULT SETTING 
Disabled 
COMMAND MODE 
Global Configuration
Interface Configuration (Ethernet, Port Channel)
COMMAND USAGE 
Loopback detection must be enabled globally for the switch by this 
command and enabled for a specific interface for this function to take 
effect. 
EXAMPLE 
This example enables general loopback detection on the switch, disables 
loopback detection provided for the spanning tree protocol on port 1, and 
then enables general loopback detection for that port.
Console(config)#loopback-detection
Console(config)#interface ethernet 1/1
Console(config-if)#no spanning-tree loopback-detection
Console(config-if)#loopback-detection
Console(config)#
loopback-detection
action
This command specifies the protective action the switch takes when a 
loopback condition is detected. Use the no form to restore the default 
setting.
SYNTAX 
loopback-detection action {block | none | shutdown} 
no loopback-detection action 
block - When a loopback is detected on a port which a member of a 
specific VLAN, packets belonging to that VLAN are dropped at the 
offending port.
none - No action is taken.
shutdown - Shuts down the interface. 
DEFAULT SETTING 
Shut down 
COMMAND MODE 
Global Configuration