Multiple Spanning Tree Protocol
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The Multiple Spanning Tree network protocol and algorithm provides a loop free topology for any LAN or bridged network. If there is only one Virtual LAN (VLAN) in the network, single (traditional) STP works appropriately. If the network contains more than one VLAN, the logical network configured by single STP would work, but it is possible to make better use of the redundant links available by using an alternate spanning tree for different (groups of) VLANs.
The Per-VLAN Multiple Spanning Tree Protocol configures a separate Spanning Tree for each VLAN and blocks the links that are redundant within each Spanning Tree. The Multiple Spanning Tree Protocol, which is also referred to as MSTP, is defined in the 2003 edition of IEEE Standard 802.1Q.
MSTP allows formation of MST regions which can run multiple MST instances (MSTI). Multiple regions and other STP bridges are interconnected using one single common spanning tree (CST).
MSTP was inspired by Cisco Systems' Multiple Instances Spanning Tree Protocol, and is an evolution of the Spanning Tree Protocol and the Rapid Spanning Tree Protocol. It was introduced in IEEE 802.1s as amendment to 802.1Q, 1998 edition. Standard IEEE 802.1Q-2003 now includes MSTP.
