Blade ICE G8000 manual Multiple Spanning Tree Protocol, Mstp Region, Common Internal Spanning Tree

RackSwitch G8000 Application Guide

Multiple Spanning Tree Protocol

Multiple Spanning Tree extends Rapid Spanning Tree Protocol through multiple Spanning Tree Groups, using multiple VLANs in each STG. MSTP supports up to 32 Spanning-Tree instances, that correspond to STP Groups 1-32.

For more information about Spanning Tree Protocol, see Chapter 5, “Spanning Tree.”

In Multiple Spanning Tree Protocol (MSTP), several VLANs can be mapped to each Span- ning-Tree instance. Each Spanning-Tree instance is independent of other instances. MSTP allows frames assigned to different VLANs to follow separate paths, each path based on an independent Spanning-Tree instance. This approach provides multiple forwarding paths for data traffic, enabling load-balancing, and reducing the number of Spanning-Tree instances required to support a large number of VLANs.

MSTP Region

A group of interconnected bridges that share the same attributes is called an MST region. Each bridge within the region must share the following attributes:

„Alphanumeric name

„Revision number

„VLAN-to STG mapping scheme

MSTP provides rapid re-configuration, scalability and control due to the support of regions, and multiple Spanning-Tree instances support within each region.

Common Internal Spanning Tree

The Common Internal Spanning Tree (CIST) provides a common form of Spanning Tree Pro- tocol, with one Spanning-Tree instance that can be used throughout the MSTP region.

CIST allows the switch to interoperate with legacy equipment, including devices that run IEEE 802.1D (1998).

CIST allows the MSTP region to act as a virtual bridge to other bridges outside of the region, and provides a single Spanning-Tree instance to interact with them.

CIST port configuration includes Hello time, path-cost, and interface priority. These parame- ters do not affect Spanning Tree Groups 1-32. They apply only when the CIST is used.

86 „ Chapter 5: Spanning Tree BMD00041, November 2008