Duplex Mismatch Explained: Why Your Network Is Slow
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Your network is slow. No obvious reason. No red alarms.
That's a duplex mismatch — and it's more common than you think.
Here's how to find it and kill it in minutes.
📌 In this video:
We cover the three essential Cisco troubleshooting commands every
network engineer reaches for first: ping to test reachability and
measure round-trip time, traceroute to follow the exact path of an
IP packet hop by hop using the TTL mechanism, and telnet to test
remote connectivity on port 23. Then we go deep on duplex mismatch
— one of the most silent and damaging issues on any Cisco network
— explaining how half duplex, full duplex, and auto-negotiation
failures cause slowness and connection drops between switches,
routers, and workstations. You'll learn to use the show interfaces
command to check duplex and speed settings, read CDP error messages
directly on the console, and apply the duplex command to fix
mismatches at the interface level. Core CCNA 200-301 troubleshooting
knowledge, straight to the point.
⏱️ Chapters:
0:00 — Is Your Network Slow? (Intro)
0:41 — Why You Must Document Every Troubleshooting Step
1:00 — Ping Command: Test Reachability & RTT
1:17 — Traceroute Command: Follow the IP Packet Path (TTL)
1:51 — Telnet Command: Remote Connectivity on Port 23
2:00 — Duplex Modes: Half, Full & Auto Explained
2:29 — How Duplex Mismatch Silently Kills Your Network
3:01 — show interfaces: Check Duplex & Speed Settings
3:08 — CDP Protocol: Detect Duplex Errors on the Console
3:30 — Interface Down Messages on the Console
3:50 — Fix It: The duplex Command in Interface Mode
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