652 | Multiple Spanning Tree Protocolw w w . d e l l . c o m | s u p p o r t . d e l l . c o mConfigure a Root GuardUse the Root Guard feature in a Layer 2 MSTP network to avoid bridging loops.You enable root guard on a per-port or per-port-channel basis.To enable a root guard on an MSTP-enabled port or port-channel interface, enter the spanning-tree mstprootguard command. Refer to STP Root Guard on page 1060 for more information on how to use the rootguard feature.To disable MSTP root guard on a port or port-channel interface, enter the no spanning-tree mstp rootguardcommand in an interface configuration mode.To verify the MSTP root guard configuration on a port or port-channel interface, enter the showspanning-tree msti [instance-number] guard command in global configuration mode.FTOS Behavior: The following conditions apply to a port enabled with root guard:• Root guard is supported on any MSTP-enabled port or port-channel interface except when used as astacking port.• Root guard is supported on a port in any Spanning Tree mode:• Spanning Tree Protocol (STP)• Rapid Spanning Tree Protocol (RSTP)• Multiple Spanning Tree Protocol (MSTP)• Per-VLAN Spanning Tree Plus (PVST+)• When enabled on a port, root guard applies to all VLANs configured on the port.• Root guard and loop guard cannot be enabled at the same time on an MSTP port. For example, if youconfigure loop guard on a port on which root guard is already configured, the following error message isdisplayed:% Error: RootGuard is configured. Cannot configure LoopGuard.• When used in an MSTP network, if root guard blocks a boundary port in the CIST, the port is also blockedin all other MST instances.Task Command Syntax Command ModeEnable root guard on a port or port-channel interface. spanning-tree mstp rootguard INTERFACEINTERFACEPORT-CHANNEL
