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Cisco Small Business SG200 Series 8-port Smart Switch 118
Spanning Tree
This chapter describes how to configure the Spanning Tree Protocol (STP) on the
switch.
It includes the following topics:
• Overview of Spanning Tree
• Configuring STP Status and Global Settings
• Configuring STP Interface Settings
• RSTP Interface Settings
Overview of Spanning Tree
STP enables efficient communication on a network that includes multiple bridges.
Devices on these networks can learn multiple (that is, redundant) paths to the
same endpoint. While path redundancy is desirable for maintaining traffic flow
when particular links are down, it can lead to a traffic loops that affect network
performance and confuse forwarding algorithms.
Each STP-enabled bridge exchanges Bridge Protocol Data Units (BPDUs) with
other bridges. BPDUs identify the bridge port MAC addresses and the priority and
cost associated with each port. STP uses this information to build a topology that
provides one active path between any two stations on the network. Duplicate
paths between those stations are placed in a stand-by state for use only when the
active path becomes unavailable.
BPDU exchanges also facilitate the election of a root bridge and root port for the
network. The root bridge provides a reference point that each other bridge uses to
calculate a lowest-cost path by summing the cost of the ports in each path and
choosing the one with the lowest total. The port that connects a bridge to the
lowest-cost path is called the bridge’s root port.