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19 Spanning Tree Protocol
19.1 Overview of Spanning Tree Protocols
19.1.1 Overview
The Spanning Tree Protocol is a Layer 2 loop prevention protocol. The Spanning Tree
Protocol can be used to make Layer 2 networks redundant, and prevent loops.
The following figure provides an overview of a network with a Spanning Tree Protocol
applied.
Figure 19-1 Overview of a network with a Spanning Tree Protocol applied
In the configuration in the diagram, the switches responsible for the network core are made
redundant, as are the communication paths from the edge switch handling the terminals.
By making the switches and communication paths redundant, transmission can carry over
to an alternate path when a fault occurs on the normal communication path.
A Layer 2 loop configuration is one in which a Layer 2 network is made redundant. Layer 2
loops cause broadcast storms and destabilize MAC address learning. Spanning Tree
Protocols prevent loops on Layer 2 networks in redundant loop configurations, by choosing
locations in which to stop communication, and putting them in the Blocking status.
19.1.2 Types of Spanning Tree Protocols
The Switch supports three types of Spanning Tree Protocols: PVST+, Single Spanning
Tree, and Multiple Spanning Tree. Each Spanning Tree Protocol is built differently. The
following table provides an overview of the types of Spanning Tree Protocols.
Table 19-1 Types of Spanning Tree Protocols
Model name
PVST+
Single Spanning Tree
296
Build unit
Per-VLAN
At the switch level
Overview
This kind of tree is built per VLAN. If multiple VLANs
belong to a single port, different tree build results
are applied to each VLAN.
This kind of tree is built with all ports on the switch
as targets. The tree build results are applied to all
ports on the switch regardless of the VLAN
configuration.
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