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Usage Guide: When there is no loopback detection, the detection interval can be
relatively shorter, for too short a time would be a disaster for the whole network if there is
any loopback. So, a relatively longer interval is recommended when loopbacks exist.
Example: Set the loopback diction interval as 35, 15.
Switch(config)#loopback-detection interval-time 35 15
3.3.5 loopback-detection specified-vlan
Command: loopback-detection specified-vlan <vlan-list>
no loopback-detection specified-vlan [<vlan-list>]
Function: Enable the function of loopback detection on the port and specify the VLAN to
be checked; the no operation of this command will disable the function of detecting
loopbacks through this port or the specified VLAN.
Parameters: <vlan-list> the list of VLANs allowed passing through the port. Given the
situation of a trunk port, the specified VLANs can be checked. So this command is used to
set the vlan list to be checked.
Default: Disable the function of detecting the loopbacks through the port.
Command mode: Port Mode.
Usage Guide: If a port can be a TRUNK port of multiple Vlans, the detection of loopbacks
can be implemented on the basis of port+Vlan, which means the objects of the detection
can be the specified Vlans on a port. If the port is an ACCESS port, only one Vlan on the
port is allowed to be checked despite the fact that multiple Vlans can be configured. This
function is not supported under Port-channel.
Example: Enable the function of loopback detection under port 1/2 mode.
Switch(config)#interface ethernet 1/2
Switch(Config-If-Ethernet1/2)#switchport mode trunk
Switch(Config-If-Ethernet1/2)#switchport trunk allowed vlan all
Switch(Config-If-Ethernet1/2)#loopback-detection specified-vlan 1;3;5-20
Switch(Config-If-Ethernet1/2)#no loopback-detection specified-vlan 1;3;5-20
3.3.6 show loopback-detection
Command: show loopback-detection [interface <interface-list>]
Function: Display the state of loopback detection on all ports if no parameter is provided,
or the state and result of the specified ports according to the parameters.
Parameters: <interface-list> the list of ports to be displayed, for Example: ethernet 1/1.
Command mode: Admin and Configuration Mode.
Usage Guide: Display the state and result of loopback detection on ports with this