Jeremy's IT Lab: CCNA Spanning Tree Part 2

Introduction

• Continuation of spanning tree studies.
• Focus on the operation of spanning tree, spanning tree states, timers, BPDU, optional features (spanning tree toolkit), and configurations.

Spanning Tree States

• Stable States:
  • Blocking: Non-designated ports, prevents loops, does not forward traffic, receives BPDUs.
  • Forwarding: Sends and receives traffic and BPDUs, learns MAC addresses.
• Transitional States:
  • Listening: 15 seconds by default (Forward delay timer), only sends/receives BPDUs, no traffic or MAC learning.
  • Learning: 15 seconds by default, like Listening but learns MAC addresses.
• Other States:
  • Disabled: Administratively shut down.

Spanning Tree Timers

• Hello Timer: Determines BPDU send intervals, default every 2 seconds.
• Forward Delay Timer: Length of Listening and Learning states, default 15 seconds each.
• Max Age Timer: Time an interface waits without receiving BPDUs before reevaluating, default 20 seconds.

Bridge Protocol Data Unit (BPDU)

• Fields:
  • Protocol Identifier: 0000
  • Protocol Version Identifier
  • BPDU Type
  • Flags
  • Root Identifier: bridge priority, MAC address, etc.
  • Root Path Cost
  • Port Identifier
  • Timers: Message age, Max age, Hello, Forward Delay.

Optional Spanning Tree Features

• PortFast: Bypasses Listening and Learning states for ports connected to end hosts, risks loops if connected to another switch.
• BPDU Guard: Shuts down ports receiving BPDUs to prevent loops.
• Root Guard: Prevents a port from becoming a root port if superior BPDU is received.
• Loop Guard: Prevents interface from causing loops if it stops receiving BPDUs.

Spanning Tree Configuration

• Mode Configuration:
  • MST, PVST, Rapid-PVST.
  • Rapid-PVST is default on modern Cisco switches.
• Root Bridge Configuration:
  • Use SPANNING-TREE VLAN <number> ROOT PRIMARY/SECONDARY.
  • Helps with load balancing across VLANs.
• Port Settings:
  • Cost and Port Priority can be set per VLAN.

Practice and Quiz

• Suggested using Packet Tracer for practical labs.
• Key quiz questions reviewed, focusing on PortFast, BPDU Guard, and spanning tree timers.
• Recommended Boson ExSim for practice exams.

Conclusion

• Encourage studying and practicing with provided materials (flashcards, lab videos).
• Acknowledgement of supporters and call to action (subscribe, share, etc.).

Additional Resources

• Review flashcard deck available.
• Packet tracer lab for hands-on practice.