Why Does STP Block a Port? | Cisco STP Explained | CCNA Lab 05

Why does a Cisco switch block a port even when the physical link is connected? 🤔 In this hands-on Cisco Packet Tracer lab, we'll understand Spanning Tree Protocol (STP), learn how the Root Bridge is elected, identify Root Ports, Designated Ports and Alternate Ports, and see what happens when a network link fails. If you're preparing for the CCNA certification or learning Cisco switching, this practical STP tutorial will help you understand how switches prevent Layer 2 loops while maintaining redundant paths. 🔹 *WHAT YOU'LL LEARN* ✅ Why Layer 2 switching loops occur ✅ What is Spanning Tree Protocol (STP) and why it is required ✅ How the Root Bridge election works ✅ Understanding Bridge ID, priority and MAC address ✅ Root Port vs Designated Port vs Alternate Port ✅ Classic STP port states: Blocking, Listening, Learning, Forwarding and Disabled ✅ Configure STP priority in Cisco switches ✅ Verify STP using `show spanning-tree vlan 10` ✅ Understand how STP responds to a link failure ✅ Observe alternate path activation and network recovery 💻 *COMMANDS COVERED* `vlan 10` `switchport mode access` `switchport access vlan 10` `spanning-tree vlan 10 priority 4096` `spanning-tree vlan 10 priority 8192` `show spanning-tree vlan 10` `show spanning-tree root` `show spanning-tree blockedports` `shutdown` `no shutdown` 🧪 *ABOUT THIS PACKET TRACER LAB* We use three Cisco switches connected in a triangle topology, with two PCs connected at the edge. All inter-switch links are configured as access ports in VLAN 10. We deliberately create a redundant Layer 2 topology and observe how STP selects the forwarding and non-forwarding paths. We then simulate a link failure and verify how the alternate path takes over after STP convergence. 🎯 *WHO SHOULD WATCH?* CCNA 200-301 students Beginners learning Cisco switching Networking students practising Packet Tracer Junior network engineers learning STP fundamentals 📌 *IMPORTANT NOTE* This tutorial demonstrates classic STP (IEEE 802.1D) terminology and behaviour. RSTP uses different port-state terminology and convergence behaviour. 💬 *TEST YOUR CCNA KNOWLEDGE* Why does STP place one port into the Blocking state when multiple redundant Layer 2 paths exist? And what happens to an Alternate Port when the active Root Port fails? Share your answers in the comments! 📚 *ABOUT QUERYIT NETWORKS* Enterprise Networking Simplified. Practical Cisco networking, routing, switching, cloud and firewall security tutorials. Subscribe for more CCNA Packet Tracer labs and real-world networking concepts. #STP #CCNA #CiscoNetworking #queryitnetwork #cisco