Cisco WS-C3560E-48PD-SF Command Reference - Page 605

Chapter 2 Catalyst 3560 Switch Cisco IOS Commands spanning-tree guard Loop guard is most effective when it is configured on the entire switched network. When the switch is operating in PVST+ or rapid-PVST+ mode, loop guard prevents alternate and root ports from becoming designated ports, and spanning tree does not send bridge protocol data units (BPDUs) on root or alternate ports. When the switch is operating in MST mode, BPDUs are not sent on nonboundary interfaces if the interface is blocked by loop guard in all MST instances. On a boundary interface, loop guard blocks the interface in all MST instances. To disable root guard or loop guard, use the spanning-tree guard none interface configuration command. You cannot enable both root guard and loop guard at the same time. You can override the setting of the spanning-tree loopguard default global configuration command by using the spanning-tree guard loop interface configuration command. Examples This example shows how to enable root guard on all the VLANs associated with the specified port: Switch(config)# interface gigabitethernet0/2 Switch(config-if)# spanning-tree guard root This example shows how to enable loop guard on all the VLANs associated with the specified port: Switch(config)# interface gigabitethernet0/2 Switch(config-if)# spanning-tree guard loop You can verify your settings by entering the show running-config privileged EXEC command. Related Commands Command show running-config spanning-tree cost spanning-tree loopguard default spanning-tree mst cost spanning-tree mst port-priority spanning-tree mst root spanning-tree port-priority spanning-tree vlan priority Description Displays the current operating configuration. For syntax information, select Cisco IOS Configuration Fundamentals Command Reference, Release 12.2 > File Management Commands > Configuration File Management Commands. Sets the path cost for spanning-tree calculations. Prevents alternate or root ports from becoming designated ports because of a failure that leads to a unidirectional link. Configures the path cost for MST calculations. Configures an interface priority. Configures the MST root switch priority and timers based on the network diameter. Configures an interface priority. Sets the switch priority for the specified spanning-tree instance. 78-16405-05 Catalyst 3560 Switch Command Reference 2-573