Blade ICE G8000 - Manual (Page 86)

RackSwitch G8000 Application Guide
86 „ Chapter 5: Spanning Tree BMD00041, November 2008
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.