Multiple Spanning Tree - Cisco Catalyst 4500 Series Configuration Manual

Chapter 1 Product Overview

Multiple Spanning Tree

IEEE 802.1s Multiple Spanning Tree (MST) allows for multiple spanning tree instances within a single
802.1Q or Inter-Switch Link (ISL) VLAN trunk. MST extends the IEEE 802.1w Rapid Spanning Tree
(RST) algorithm to multiple spanning trees. This extension provides both rapid convergence and load
balancing within a VLAN environment.
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).
For information on configuring MST, see
Per-VLAN Rapid Spanning Tree
Per-VLAN Rapid Spanning Tree (PVRST+) is the implementation of 802.1w on a per-VLAN basis. It is
the same as PVST+ with respect to STP mode and runs RSTP protocol based on 802.1w.
For information on configuring PVRST+, see
Quality of Service
Note QoS functionality on Catalyst 4900M, Catalyst 4948E, Supervisor Engine 6-E and Supervisor
Engine 6L-E are equivalent.
The quality of service (QoS) feature prevents congestion by selecting network traffic and prioritizing it
according to its relative importance. Implementing QoS in your network makes network performance
more predictable and bandwidth use more effective.
The Catalyst 4500 series switch supports the following QoS features:
•
•
•
Catalyst 4500 series switch supports trusted boundary, which uses the Cisco Discovery Protocol (CDP)
to detect the presence of a Cisco IP phone (such as the Cisco IP Phone 7910, 7935, 7940, and 7960) on
a switch port. If the telephone is not detected, the trusted boundary feature disables the trusted setting
on the switch port and prevents misuse of a high-priority queue.
The Catalyst 4500 series switch also supports QoS Automation (Auto QoS), which simplifies the
deployment of existing QoS features through automatic configuration.
Cisco Modular QoS Command-Line-Interface
Cisco Modular QoS CLI (MQC) is the framework that implements Cisco IOS software QoS. MQC
allows the user to define a traffic class, create a traffic policy (containing the QoS feature to be applied
to the traffic class), and attach the traffic policy to an interface. MQC is a cross-Cisco baseline that
provides a consistent syntax and behavior of QoS features across multiple product families. Cisco IOS
OL-25340-01
Classification and marking
Ingress and egress policing, including per-port per-VLAN policing
Sharing and shaping
Chapter 20, "Configuring STP and MST."
Chapter 20, "Configuring STP and MST."
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
Layer 2 Software Features
1-7