There is a lot of confusion about auto negotiation. Here is a chart that will help bring things into perspective.
Autonegotiation Valid Configuration
|
Configuration NIC (Speed/Duplex) |
Configuration Switch (Speed/Duplex) |
Resulting NIC Speed/Duplex |
Resulting Catalyst Speed/Duplex |
Comments |
|---|---|---|---|---|
|
AUTO |
AUTO |
1000 Mbps, Full-duplex |
1000 Mbps, Full-duplex |
Assuming maximum capability of Catalyst switch, and NIC is 1000 |
|
1000 Mbps, Full-duplex |
AUTO |
1000 Mbps, Full-duplex |
1000 Mbps, Full-duplex |
Link is established, but the switch does not see any |
|
AUTO |
1000 Mbps, Full-duplex |
1000 Mbps, Full-duplex |
1000 Mbps, Full-duplex |
Assuming maximum capability of NIC is 1000 Mbps, |
|
1000 Mbps, Full-duplex |
1000 Mbps, Full-duplex |
1000 Mbps, Full-duplex |
1000 Mbps, Full-duplex |
Correct Manual Configuration |
|
100 Mbps, Full-duplex |
1000 Mbps, Full-duplex |
No Link |
No Link |
Neither side establishes link, due to speed |
|
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 |
Correct Manual |
|
100 Mbps, Half-duplex |
AUTO |
100 Mbps, Half-duplex |
100 Mbps, Half-duplex |
Link is established, but switch does not see any |
|
10 Mbps, Half-duplex |
AUTO |
10 Mbps, Half-duplex |
10 Mbps, Half-duplex |
Link is established, but switch does not see Fast Link Pulse |
|
10 Mbps, Half-duplex |
100 Mbps, Half-duplex |
No Link |
No Link |
Neither side establishes link, due to speed |
|
AUTO |
100 Mbps, Half-duplex |
100 Mbps, Half-duplex |
100 Mbps, Half-duplex |
Link is established, but NIC does not see any autonegotiation |
|
AUTO |
10 Mbps, Half-duplex |
10 Mbps, Half-duplex |
10 Mbps, Half-duplex |
Link is established, but NIC does not see FLP and defaults to |
