New Training: Fundamentals of STP (Spanning Tree Protocol)

In this 9-video skill, CBT Nuggets trainer Keith Barker explains how switches prevent Layer 2 loops in networks that have redundant links. Gain an understanding of root bridges, designated ports, how non-root bridges select root ports, and how blocked ports are verified in spanning tree. Watch this new Cisco training.

Watch the full course: Cisco CCNP Enterprise Core

This training includes:

• 9 videos

• 1.3 hours of training

You’ll learn these topics in this skill:

• Welcome to STP Fundamentals

• The Challenge of Layer 2 Redundancy

• A Strategy for Solving Layer 2 Loops

• STP Tools of the Trade

• How STP Elects the Root Bridge

• Selecting the Root Port

• Selecting Designated Ports

• Blocking

• Review

Spanning Tree Protocol Prevents the Dangers of Infinite Loops

Say you wanted to create a text message chain for your group of Ultimate Frisbee friends so that everyone always knew when games and practices were happening. You collected everyone’s phone numbers and then made a chart with the team coach at the top. She texts three people. They each text three people, they each text three more people, and then one of the people at the bottom texts the coach to say “everyone got the message”.

A while later, a clever programmer comes along and says, “I can automate that!” They write a program that automatically forwards any message each phone receives about scheduling and uses the same chart of phone numbers. But that programmer didn’t account for the confirmation message the coach gets at the end. So the computer program takes that message and sends it through the chart again. And then when it receives the confirmation of that, it sends it all over again — and over and over again infinitely.

This is a simple, and maybe silly, metaphor for a networking problem from the past: what can happen when you try to map a network with a redundancy or failover port assigned. Humans can spot a problem like that quickly, but computers struggle to differentiate between network traffic and false positives. It was Spanning Tree Protocol that fixed it. It’s an ingenious and complicated mathematical solution that basically made wide area networks much, much easier to configure and map.