Layer 2 Troubleshooting - STP Loops, MAC Tables, Duplex Mismatch - Network+ N10-009
Watch on YouTube Layer 2 failures break entire network segments in seconds, and this Network+ N10-009 walkthrough covers the five families every candidate must recognize. Spanning Tree Protocol loops and broadcast storms, MAC table flooding and port security lockouts, duplex mismatch with its late collision and FCS error signature, VLAN mis-assignment on access and trunk ports, and ARP problems including gratuitous ARP and cache poisoning. Includes the exact show commands on Cisco IOS, Juniper Junos, Arista EOS, and Linux bridges so you can prove which failure family you are facing on any vendor. Watch the next video in the playlist for Layer 3 troubleshooting - routing loops, ACL denies, and MTU problems.
▶ Watch next: Layer 3 Troubleshooting - Routing Loops, ACLs, and MTU Blackholes - Network+ N10-009 https://www.youtube.com/watch?v=6veLbsau8tw
📺 Full playlist: CompTIA Network+ N10-009 (2026) https://www.youtube.com/playlist?list=PLlIAFxS29649uKqbaM7zlD_I6e9GazVaQ
Chapters
- 0:00 Layer Two Symptoms Look Like the Apocalypse
- 2:48 STP Failures and the BPDU Trust Problem
- 5:43 MAC Tables, Flooding, and Port Security Lockouts
- 8:19 Duplex Mismatch, the Silent Throughput Killer
- 10:32 VLAN Mis-Assignment and ARP Trouble
- 13:20 Troubleshooting Commands Across Vendors
- 16:31 Quiz Time
Layer 2 failures break entire network segments in seconds, and this Network+ N10-009 walkthrough covers the five families every candidate must recognize. Spanning Tree Protocol loops and broadcast storms, MAC table flooding and port...
Key Topics
- Layer Two Symptoms Look Like the Apocalypse
- STP Failures and the BPDU Trust Problem
- MAC Tables, Flooding, and Port Security Lockouts
- Duplex Mismatch, the Silent Throughput Killer
- VLAN Mis-Assignment and ARP Trouble
- Troubleshooting Commands Across Vendors