RSTP and MSTP
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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 status STP port state RSTP port state
Enabled Blocking Discarding
Enabled Listening Discarding
Enabled Learning Learning
Enabled Forwarding Forwarding
Disabled Disabled Discarding
