switch>(enable) set spantree backbonefast

Commands to Use for Troubleshooting The Configuration：

show spantree vlan_id - Shows the current state of the spanning tree for the ”vlan_id” entered from the perspective of the switch on which it is entered.

show spantree summary - Provides a summary of connected spanning tree ports by VLAN.

show spantree statistics - Shows spanning tree statistical information.

show spantree backbonefast - Displays whether the spanning tree Backbone Fast Convergence feature is enabled.

show spantree blockedports - Displays only the blocked ports.

show spantree portstate - Determines the current spanning tree state of a Token Ring port within a spanning tree.

show spantree portvlancost - Shows the path cost for the VLANs on a port.

show spantree uplinkfast - Shows the uplinkfast settings.

IEEE 802.1s MST Overview

Releases 12.1(11b)EX and later releases support MST. MST in this release is based on the draft version of the IEEE standard. 802.1s for MST is an amendment to 802.1Q. MST extends the IEEE 802.1w rapid spanning tree (RST) algorithm to multiple spanning trees. This extension provides both rapid convergence and load balancing

in a VLAN environment. MST converges faster than PVST+. MST is backward compatible with 802.1D STP, 802.1w (rapid spanning tree protocol [RSTP]：There are only three port states left in RSTP：Learning, Forwarding, Discarding corresponding to the three possible operational states. The 802.1dstates disabled, blocking, and listening have been merged into a unique 802.1w discarding state.), and the Cisco PVST+ architecture.

MST allows you to build multiple spanning trees over trunks. You can group and associate VLANs to spanning tree instances. Each instance can have a topology independent of other spanning tree instances. This new architecture provides multiple forwarding paths for data traffic and enables load balancing. Network fault

tolerance is improved because a failure in one instance (forwarding path) does not affect other instances(forwarding paths).

In large networks, you can more easily administer the network and use redundant paths by locating different VLAN and spanning tree instance assignments in different parts of the network. A spanning tree instance can exist only on bridges that have compatible VLAN instance assignments. You must configure a set of bridges

with the same MST configuration information, which allows them to participate in a specific set of spanning tree instances. Interconnected bridges that have the same MST configuration are referred to as an MST region.