OmniSwitch AOS Release 6 Network Configuration Guide September 2009 page 12-1
12 Using 802.1Q 2005
Multiple Spanning Tree
The Alcatel-Lucent Multiple Spanning Tree (MST) implementation provides support for the Multiple
Spanning Tree Protocol (MSTP) as defined in the IEEE 802.1Q 2005 standard. In addition to the 802.1D
Spanning Tree Algorithm and Protocol (STP) and the 802.1w Rapid Spanning Tree Algorithm and Proto-
col (RSTP), MSTP also ensures that there is always only one data path between any two switches for a
given Spanning Tree instance to prevent network loops.
MSTP is an enhancement to the 802.1Q Common Spanning Tree (CST), which is provided when an
Alcatel-Lucent switch is running in the flat Spanning Tree operating mode. The flat mode applies a single
spanning tree instance across all VLAN port connections on a switch. MSTP allows the configuration of
Multiple Spanning Tree Instances (MSTIs) in addition to the CST instance. Each MSTI is mapped to a set
of VLANs. As a result, flat mode can support the forwarding of VLAN traffic over separate data paths.
In addition to MSTP support, the STP and RSTP are still available in either the flat or 1x1 mode.
However, if using STP or RSTP in the flat mode, the single Spanning Tree instance per switch algorithm
applies.
In This Chapter
This chapter describes MST in general and how MSTP works on the switch. It provides information about
configuring MSTP through the Command Line Interface (CLI). For more details about the syntax of
commands, see the OmniSwitch CLI Reference Guide. For more information about Spanning Tree
configuration commands as they apply to all supported protocols (STP, RSTP, and MSTP), see
Chapter 13, “Configuring Spanning Tree Parameters.”
The following topics are included in this chapter as they relate to the Alcatel-Lucent implementation of the
MSTP standard:
• “MST General Overview” on page 12-4.
• “MST Configuration Overview” on page 12-10.
• “Using Spanning Tree Configuration Commands” on page 12-10.
• “MST Interoperability and Migration” on page 12-12.
• “Quick Steps for Configuring an MST Region” on page 12-14.
• “Quick Steps for Configuring MSTIs” on page 12-16.
• “Verifying the MST Configuration” on page 12-19.
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