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Switching loops and Spanning Tree

Why Layer 2 loops take networks down, how Spanning Tree elects a root and blocks redundant paths, and how edge-port protections stop the loop someone plugs in at a desk.

Level
Intermediate
Length
About 50 minutes
Contents
3 lessons · 1 video · final exam
Status
Published · updated 1 Oct 2026
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Skills you'll practise

  • Recognize the symptoms of a switching loop in logs and monitoring
  • Predict the root bridge, root ports and blocked ports from bridge IDs and path costs
  • Configure edge ports with PortFast and BPDU guard and explain what each does
  • Contain a live loop safely and remove its cause

Course outline

  1. 1.Switching loops and Spanning TreeVideo · 2 min
  2. 2.Why loops are so destructiveLesson · 15 min
  3. 3.How Spanning Tree builds the treeLesson · 15 min
  4. 4.Protecting the edge and containing a loopLesson · 15 min
  5. 5.Switching loops and Spanning Tree: knowledge checkKnowledge check · 18 questions
  6. 6.Switching loops and Spanning Tree: practical exerciseKnowledge check · 1 question
  7. 7.The whole third floor froze at 10:41Scenario
  8. 8.Final exam6 questions · passing it completes the course, so people who already know the material can test out

Sources it draws on

The lessons and questions are written from these references, so learners can go back to the original.

  • IEEE 802.1D: MAC Bridges (Spanning Tree Protocol; RSTP incorporated in the 2004 edition)
  • IEEE 802.1w: Rapid Reconfiguration of Spanning Tree
  • IEEE 802.1Q: Bridges and Bridged Networks (includes MSTP)

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