Administrator Guide

Spanning Tree Protocol (STP)

The spanning tree protocol (STP) is a Layer 2 protocol — specied by IEEE 802.1d — that eliminates loops in a bridged topology by

enabling only a single path through the network.

Topics:

• Protocol Overview

• Congure Spanning Tree

• Important Points to Remember

• Conguring Interfaces for Layer 2 Mode

• Enabling Spanning Tree Protocol Globally

• Adding an Interface to the Spanning Tree Group

• Modifying Global Parameters

• Modifying Interface STP Parameters

• Enabling PortFast

• Preventing Network Disruptions with BPDU Guard

• Selecting STP Root

• STP Root Guard

• Enabling SNMP Traps for Root Elections and Topology Changes

• STP Loop Guard

• Displaying STP Guard Conguration

Protocol Overview

By eliminating loops, STP improves scalability in a large network and allows you to implement redundant paths, which can be activated after

the failure of active paths. Layer 2 loops, which can occur in a network due to poor network design and without enabling protocols like

xSTP, can cause unnecessarily high switch CPU utilization and memory consumption.

The system supports three other versions of spanning tree, as shown in the following table.

Table 103. Dell Networking OS Supported Spanning Tree Protocols

Dell Networking Term IEEE Specication

Spanning Tree Protocol (STP) 802.1d

Rapid Spanning Tree Protocol (RSTP) 802.1w

Multiple Spanning Tree Protocol (MSTP) 802.1s

Per-VLAN Spanning Tree Plus (PVST+) Third Party

Congure Spanning Tree

Conguring spanning tree is a two-step process.

• Conguring Interfaces for Layer 2 Mode

970 Spanning Tree Protocol (STP)