Multiple Spanning Tree Protocol

Multiple Spanning Tree Protocol (MSTP), based on IEEE 802.1Q-2003 (formerly known as IEEE 802.1s), allows the bundling of multiple VLANs into one spanning tree topology.

MSTP logically divides a Layer 2 network into regions. Each region has a unique identifier and contains multiple spanning tree instances (MSTIs). An MSTI is a spanning tree domain that operates within and is bounded by a region. MSTIs control the topology inside the regions. The Common and Internal Spanning Tree (CIST) is a single spanning tree domain that interconnects MSTP regions. The CIST is responsible for creating a loop-free topology by exchanging and propagating BPDUs across regions to form a Common Spanning Tree (CST).

MSTP treats each switch as its own region, identified by the switch's MAC address. A single Common and Internal Spanning Tree (CIST) is built across all of your sites.

ExtremeCloud-enabled switches implement standard MSTP for network loop protection. By default, MSTP is disabled but can be enabled in the Administration section of the user interface. Enabling MSTP enables it on all of the cloud-enabled switches in a ExtremeCloud-enabled network.

The bridge priority for switches is set to defaults that are based on the switch model. These defaults are selected to discourage cloud-enabled switches from becoming the root of a spanning tree. More powerful cloud-enabled switches are assigned priorities that will cause them to be more likely to be selected as a spanning tree root node than a pure edge switch. However, the defaults can be overridden.

Port is automatically classified as edge if the port's function is set to AP or Host. Edge-Safeguard and BDPU-Restrict (or BDPU Guard) are applied to edge ports automatically. If a port's function is inter-switch, the port is classified as point-to-point and loop protect (or loop guard) is applied. For more information about these Extreme EXOS features, see the EXOS documentation at http://extremenetworks.com/support/documentation.