User Guide for the Avaya P580 and P882 Multiservice Switches, v6.1 7-1
7Configuring Rapid

Spanning Tree

Overview
Contents This chapter contains the following sections:
■How RSTP Achieves Rapid Recovery
■Spanning Tree Configurations
■Configuring Global Spanning Tree Options
■Viewing Global Spanning Tree Information
■Configuring Spanning Tree Bridges
■Viewing Bridge Port Information
■Configuring a Bridge Port
■Configuring Spanning Tree Settings for Switch Ports

Purpose of

Spanning Tree STP prevents loops in layer 2 networks that have redundant paths. Loops in
layer 2 networks can result in duplicate frames and switches learning the
same MAC addresses on multiple interfaces.
To prevent loops, STP calculates a single path through the n etwork and th en
blocks any redundant paths. STP first identifies a root switch and then
identifies the most efficient path from the root switch to each switch in the
network. Any redundant paths that exist enter a blocked state.
If a network segment in the spanning tree becomes unreachable or if you
change the cost of a path, Spanning Tree recalculates a path through the
network and then activates the new best path.
RSTP vs. STP In application software v6.0 and later, the Rapid Spanning Tree Protocol
(RSTP) replaces the 802.1D Spanning Tree Protocol (STP). STP is
relatively slow at recovering from a failure in the network. RSTP was
created to decrease this recovery time.
When a switch is running RSTP, a port can change from blocking to
forwarding more quickly than when the switch is running STP. This
decrease in transition time makes it possible for RSTP to recover more
quickly from failures in the network.