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
- 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.
- 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
- Check Configuration: Verify both NIC and switch settings.
- Monitor Performance: Look for signs of duplex mismatches like slow network speeds or collisions.
- 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