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OmniSwitch 6600 Family Network Configuration Guide April 2006 page 5-1
5 Configuring Spanning Tree
Parameters
The Spanning Tree Algorithm and Protocol (STP) is a self-configuring algorithm that maintains a loop-
free topology while providing data path redundancy and network scalability. Based on the IEEE 802.1D
standard, the Alcatel STP implementation distributes the Spanning Tree load between the Chassis
Management Module (CMM) and the Network Interface modules (NIs). This ensures a Spanning Tree that
continues to respond to STP Bridge Protocol Data Units (BPDU) received on switch ports and port link up
and down states in the event of a CMM fail over to a backup CMM. In addition, the Alcatel distributed
implementation incorporates the following Spanning Tree features:
• Configures a physical topology into a single Spanning Tree to ensure that there is only one data path
between any two switches.
• Supports fault tolerance within the network topology. The Spanning Tree is reconfigured in the event
of a data path or bridge failure or when a new switch is added to the topology.
• Supports two Spanning Tree operating modes; flat (single STP instance per switch) and 1x1 (single
STP instance per VLAN).
• Supports three Spanning Tree Algorithms; 802.1D (STP), 802.1w (RSTP), and 802.1s (MSTP).
• Allows 802.1Q tagged ports and link aggregate logical ports to participate in the calculation of the STP
topology.
The Distributed Spanning Tree software is active on all switches by default. As a result, a loop-free
network topology is automatically calculated based on default Spanning Tree switch, bridge, and port
parameter values. It is only necessary to configure Spanning Tree parameters to change how the topology
is calculated and maintained.
In This Chapter
This chapter provides an overview about how Spanning Tree works and how to configure Spanning Tree
parameters through the Command Line Interface (CLI). CLI commands are used in the configuration
examples; for more details about the syntax of commands, see the OmniSwitch CLI Reference Guide.
Configuration procedures described in this chapter include:
• Selecting the switch Spanning Tree operating mode (flat or 1x1) on page 5-9.
• Configuring Spanning Tree bridge parameters on page 5-12.
• Configuring Spanning Tree port parameters on page 5-19.
• Configuring an example Spanning Tree topology on page 5-29