Quiz Entry - updated: 2026.07.14
What are duplex settings and what problems can duplex mismatch cause?
Full-duplex sends and receives simultaneously; half-duplex only one direction at a time. A duplex mismatch (one side full, one side half) is a top cause of slow 10/100 links, late collisions and CRC errors.
Duplex Settings:
| Mode | Description | Usage |
|---|---|---|
| Full-duplex | Both ends can send and receive simultaneously | Modern switches, point-to-point links |
| Half-duplex | Only one end can send at a time | Legacy hubs, wireless |
Autonegotiation:
- Switches and NICs automatically negotiate speed and duplex
- Enabled by default on most modern devices
Duplex Mismatch Problem:
- Occurs when one side is full-duplex and other is half-duplex
- One of the most common causes of performance issues on 10/100 Mbps links
- Symptoms: slow performance, late collisions, CRC errors
Best practice:
- Either enable autonegotiation on BOTH sides
- Or manually configure BOTH sides to the same settings
- Gigabit Ethernet ports only operate in full-duplex
Go deeper:
-
Autonegotiation — incl. duplex mismatch (Wikipedia) — how link partners agree on speed and duplex, and why a mismatch produces late collisions and FCS errors. -
Duplex — telecommunications (Wikipedia) — the full- vs half-duplex distinction underlying the whole problem.