Spanning-Tree Operation

802.1s Multiple Spanning Tree Protocol (MSTP)

Syntax: spanning-tree < port-list> root-guard

MSTP only. When a port is enabled as root-guard, it cannot be selected as the root port even if it receives superior STP BPDUs. The port is assigned an “alternate” port role and enters a blocking state if it receives superior STP BPDUs. The BPDUs received on a port enabled as root-guardare ignored. All other BPDUs are accepted and the external devices may belong to the spanning tree as long as they do not claim to be the Root device.

Syntax: spanning-tree < port-list> tcn-guard

When tcn-guardis enabled for a port, it causes the port to stop propagating received topology change notifications and topology changes to other ports.

(Default: No - disabled)

Configuring MST Instance Parameters

Command

 

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spanning-tree instance < 1..16

> vlan < vid> [ vid..vid ]

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no spanning-tree instance < 1..16 >

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spanning-tree instance < 1..16

> priority < 0..15 >

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spanning-tree priority < 0..15 >

 

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Syntax: spanning-tree instance < 1..16 > vlan < vid [ vid..vid ] > no spanning-tree instance < 1..16 >

Configuring MSTP on the switch automatically configures the IST instance and places all statically configured VLANs on the switch into the IST instance. This command creates a new MST instance (MSTI) and moves the VLANs you specify from the IST to the MSTI. At least one VLAN must be mapped to a MSTI when you create it. (A VLAN cannot be mapped to more than one instance at a time.) You can create up to 16 MSTIs in a region. Use the no form of the command to remove a VLAN from an MSTI. (Removing a VLAN from an MSTI returns the VLAN to the IST instance, where it can either remain or be re­ assigned to another MSTI configured in the region.)

The no form of the command deletes the specified MSTI and returns all VLAN assignments to the region’s IST instance.

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