RSTP and MSTP

RSTP and MSTP

Introduction

Rapid Spanning Tree Protocol (IEEE 802.1w) enhances the Spanning Tree Protocol (IEEE 802.1d) to provide rapid convergence on Spanning Tree Group 1. Multiple Spanning Tree Protocol (IEEE 802.1s) extends the Rapid Spanning Tree Protocol to provide both rapid convergence and load balancing in a VLAN environment.

The following topics are discussed in this chapter:

•Rapid Spanning Tree Protocol (RSTP)

•Multiple Spanning Tree Protocol (MSTP)

Rapid Spanning Tree Protocol

Rapid Spanning Tree Protocol (RSTP) provides rapid convergence of the spanning tree and provides for fast reconfiguration critical for networks carrying delay-sensitive traffic such as voice and video. RSTP significantly reduces the time to reconfigure the active topology of the network when changes occur to the physical topology or its configuration parameters. RSTP reduces the bridged-LAN topology to a single Spanning Tree.

For more information about Spanning Tree Protocol, see the “Spanning Tree Protocol” chapter in this guide.

RSTP parameters are configured in Spanning Tree Group 1. STP Groups 2-128 do not apply to RSTP, and must be cleared. There are new STP parameters to support RSTP, and some values to existing parameters are different.

RSTP is compatible with devices that run 802.1d Spanning Tree Protocol. If the switch detects 802.1d BPDUs, it responds with 802.1d-compatible data units. RSTP is not compatible with Per VLAN Spanning Tree (PVST) protocol.

Port state changes

The port state controls the forwarding and learning processes of Spanning Tree. In RSTP, the port state has been consolidated to the following: discarding, learning, and forwarding.

Table 13 RSTP vs. STP port states

Port operational statusSTP port stateRSTP port state

 

 

 

Enabled

Blocking

Discarding

 

 

 

Enabled

Listening

Discarding

 

 

 

Enabled

Learning

Learning

 

 

 

Enabled

Forwarding

Forwarding

 

 

 

Disabled

Disabled

Discarding

 

 

 

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