Skip to content

Grading Checklist

A good response must include:

  • Identifies the root cause: duplex mismatch -- server forced to full-duplex, switch auto-negotiated to half-duplex
  • Explains the IEEE 802.3 auto-negotiation fallback behavior: when one side forces, the other side cannot negotiate and defaults to half-duplex
  • Notes that collisions and late collisions on the server are classic duplex mismatch indicators
  • Explains why the link comes up despite the mismatch (speed can be detected, duplex cannot without autoneg)
  • Shows how to verify settings using ethtool on the server and show interface on the switch
  • Correctly identifies that the fix is to set BOTH sides to auto-negotiate, or force BOTH sides to the same settings
  • Recommends auto-negotiation as the best practice (IEEE standard, required for 1000BASE-T)
  • Mentions that for Gigabit Ethernet, auto-negotiation is mandatory per spec and forcing can cause issues
  • Explains the performance impact: half-duplex side waits for carrier sense, causing collisions with full-duplex side that transmits without checking
  • Notes that "auto-negotiation is unreliable" is a myth that applies mainly to older 10/100 equipment
  • Suggests clearing interface counters after the fix and monitoring for new errors