3Com Switch 8800 Configuration Guide
Chapter 38 MSTP Region-configuration
38-1
Chapter 38 MSTP Region-configuration
38.1 Introduction to MSTP
MSTP stands for Multiple Spanning Tree Protocol, which is compatible with Spanning
Tree Protocol (STP) and Rapid Spanning Tree Protocol (RSTP).
STP is not fast in state transition. Even on a point-to-point link or a edge port, it has to
take an interval twice as long as forward delay before the port transits to the forwarding
state.
RSTP converges fast, but has the following drawback like STP: all the network bridges
in a LAN share one spanning tree and the redundant links cannot be blocked based on
VLANs. Packets of all VLANs are forwarded along one spanning tree.
MSTP makes up for the drawback of STP and RSTP. It not only converges fast, but also
allows the traffic of different VLANs to be distributed along their respective paths, which
provides a better load-balance mechanism for the redundant links.
MSTP keeps a VLAN mapping table to associate VLANs with their spanning trees.
Using MSTP, you can divide one switching network into multiple regions, each of which
can have multiple spanning trees with each one independent of others. MSTP prunes
the ring network into a loopfree tree to avoid the generation of loops and infinite
circulations. It also provides multiple redundant paths for data forwarding to implement
the load-balance mechanism of the VLAN data.
38.1.1 MSTP Concepts
There are 4 MST regions in Figure 38-1. Each region consists of four switches, all of
which run MSTP. The following introduces the concept of MSTP with the help of this
figure.
