3Com 3 What is STP?

34 CHAPTER 4: USING RESILIENCE FEATURES
Rapid Spanning Tree
Protocol (RSTP)
The Rapid Spanning Tree (RSTP) is an enhanced Spanning Tree feature.
RSTP implements the Spanning Tree Algorithm and Protocol, as defined in
the IEEE 802.1w standard.
3Com recommends that you use the Rapid S panning Tree Protocol
feature (enabled by default) to provide opt imum performance for your
network and ease of use.
Some of the benefits of RSTP are:
■Faster determination of the Active Spann ing Tree topology throughout
a bridged network.
■Support for bridges with more than 256 ports.
■Standard support for the Fast-Forwarding configur ation of edge ports.
This is currently supported by the 'Fast Start' implementation.
■Easy deployment throughout a legacy network, through backward
compatibility :
■it will default to sending 802.1D style BPDU's on a port if it receives
packets of this fo rmat.
■it is possible for some ports on a Switch to operate in RSTP
(802.1w) mode, and other ports, for example those connected to a
legacy Switch, to operate in STP (802.1D) mode.
■you have an option to force your Switch to use the legacy 802.1D
version of Spanning Tree, if required.
What is STP? STP is a bridge-based system that allows you to implement parallel paths
for network traffic and uses a loop-detection proce ss to:
■Find and disable the less efficient paths (that is, the paths that have a
lower bandwidth).
■Enable one of the less efficient paths if the most efficient path fails.
RSTP provides the same functionality as STP. For details on how the two
systems differ, see “How RSTP Differs to STP” on page38.
As an example, Figure 5 shows a network containing three LAN segments
separated by three bridges. With this config uration, each segment can
communicate with the others using two paths. W ithout STP enabled, this
configuration creates loops that cause the network to overload.