7-6
7.3 Port Loopback Detection Function Example
Figure 7-1
A typical example of port loopback detection
As shown in the above configuration, the switch will detect the existence of loopbacks in the network topology.
After enabling the function of loopback detection on the port connecting the switch with the outside network,
the switch will notify the connected network about the existence of a loopback, and control the port on the
switch to guarantee the normal operation of the whole network.
The configuration task sequence of SWITCH:
Switch(config)#loopback-detection interval-time 35 15
Switch(config)#interface ethernet 1/1
Switch(Config-If-Ethernet1/1)#loopback-detection special-vlan 1-3
Switch(Config-If-Ethernet1/1)#loopback-detection control block
If adopting the control method of block, MSTP should be globally enabled. And the correspondence between
the spanning tree instance and the VLAN should be configured.
Switch(config)#spanning-tree
Switch(config)#spanning-tree mst configuration
Switch(Config-Mstp-Region)#instance 1 vlan 1
Switch(Config-Mstp-Region)#instance 2 vlan 2
Switch(Config-Mstp-Region)#
7.4 Port Loopback Detection Troubleshooting
The function of port loopback detection is disabled by default and should only be enabled if required.
Network Topology
SWITCH