Ethernet speed and duplex configuration

Ethernet Speed and Duplex Configuration

Understanding Speed and Duplex Settings

In networking, the speed and duplex settings of Ethernet interfaces are crucial for optimal performance. Speed can be set to 10 Mbps, 100 Mbps, or 1000 Mbps, while duplex settings can be either half-duplex or full-duplex.

  • Half-Duplex: Communication occurs in one direction at a time.
  • Full-Duplex: Communication occurs simultaneously in both directions.

Common Speed and Duplex Configurations

 

NIC
(Speed
/Duplex)
Switch
(Speed
/Duplex)
Result on
NIC
Result on
Switch
Comments
AUTO AUTO 1000 Mbps,
Full-duplex
1000 Mbps,
Full-duplex
Gigabit port support only Fullduplex
1000 Mbps
/Full-duplex
AUTO 1000 Mbps
/Full-duplex
1000 Mbps
/Full-duplex
Link is established, but the switch does not see any autonegotiation information from NIC.
Since Switch supports only full-duplex operation with 1000 Mbps, they default to full-duplex, and this happens only when operating at 1000 Mbps.
1000 Mbps
/Full-duplex
1000 Mbps
/Full-duplex
1000 Mbps
/Full-duplex
1000 Mbps
/Full-duplex
Manually Configured
100 Mbps
/Full-duplex
1000 Mbps
/Full-duplex
No Link No Link Speed mismatch
100 Mbps
/Full-duplex
AUTO 100 Mbps
/Full-duplex
100 Mbps
/Half-duplex
Duplex Mismatch
AUTO 100 Mbps
/Full-duplex
100 Mbps
/Half-duplex
100 Mbps
/Full-duplex
Duplex Mismatch
100 Mbps
/Full-duplex
100 Mbps
/Full-duplex
100 Mbps
/Full-duplex
100 Mbps
/Full-duplex
Manually Configured
100 Mbps
/Half-duplex
AUTO 100 Mbps
/Half-duplex
100 Mbps
/Half-duplex
Switch does not see any autonegotiation information from NIC and defaults to halfduplex when operating at 10/100 Mbps.
10 Mbps /Halfduplex AUTO 10 Mbps /Halfduplex 10 Mbps /Halfduplex switch does not see Fast Link Pulse (FLP) and defaults to 10 Mbps half-duplex.
10 Mbps /Halfduplex 100 Mbps
/Half-duplex
No Link No Link Speed mismatch.
AUTO 100 Mbps
/Half-duplex
100 Mbps
/Half-duplex
100 Mbps
/Half-duplex
NIC does not see any autonegotiation information and
defaults to 100 Mbps, half-duplex.
AUTO 10 Mbps /Halfduplex 10 Mbps /Halfduplex 10 Mbps /Halfduplex NIC does not see Fast Link Pulse(FLP) and defaults to 10 Mbps, half-duplex.

Configuring Speed and Duplex

  1. Auto-Negotiation: Allows devices to automatically select the best speed and duplex.
    • Recommended for most scenarios.
    • Ensure both NIC and switch are set to auto.
  2. Manual Configuration: Set specific speed and duplex settings manually.
    • Useful for troubleshooting specific issues.
    • Ensure settings match on both NIC and switch to avoid mismatches.

Troubleshooting Speed and Duplex Issues

  1. Check Configuration: Verify both NIC and switch settings.
  2. Monitor Performance: Look for signs of duplex mismatches like slow network speeds or collisions.
  3. Adjust Settings: Manually configure matching speed and duplex settings if auto-negotiation fails.

Conclusion

Proper configuration of speed and duplex settings is essential for maintaining network performance and reliability. Whether using auto-negotiation or manual settings, ensuring compatibility between devices will help avoid common network issues.

 

Reference: http://www.cisco.com/warp/public/473/46.html

Leave a Reply