Understanding duplex conflicts

What is duplex, and what is the difference between half and full duplex? What is a duplex mismatch? How can auto-negotiation help or hurt your network? How can you resolve duplex conflicts? Here's some help.

Duplex mismatch

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In this tip, David Davis helps networking engineers and newcomers understand the issues behind one of the most troublesome problems in today's networks.

Why duplex conflicts plague the network
Duplex mismatch problems -- caused by two ends of the Ethernet attempting a full-duplex connection, resulting in packet loss -- simply will not go away. After a decade of plaguing IP networks, duplex conflicts still seem to be the single worst source of performance degradation. Trivial to fix but ridiculously hard to identify and localize, mismatches recur frequently, as interfaces go up and down over time and network hosts are updated and changed. In this column, Loki Jorgensen explores why duplex mismatches are difficult to conquer using auto-negotiation.

Stop the conflicts
Today, the majority of modern cabling supports full-duplex, and there is a significantly diminished need for half-duplex -- or at least, that is what one would like to think. This column by Loki Jorgenson examines extenuating circumstances where half-duplex may be appropriate and offers best practices where its use may still be needed.

Detecting duplex mismatches
Learn how to detect and solve one of the more annoying performance issues on an Ethernet network.

This was first published in September 2006

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