乙太網 Auto-Negotiation 和手動設定等連接組合的結果，從Cisco官網資訊整理

自動協商(Auto Negotiation) 是乙太網的一個很棒的功能，任何網路口接上線以後，我們不需要擔心任何速度(Speed)、雙工(Duplex)的設定內容，硬體自動就幫我們找到最好的設定。

EW線地鐵橋下的Upper Changi Road景觀。新加坡。

有趣的是，如果交換器端設定成手動，結果電腦端忘了做任何設定(預設是自動協商)，或者是兩者設定對調，結果竟然是速度很差的 半雙工！

截自Cisco網站內容，Table 1—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 Mbps, full-duplex.
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 Catalyst switches support only full-duplex operation with 1000 Mbps, they default to full-duplex, and this happens only when operating at 1000 Mbps.
AUTO	1000 Mbps, Full-duplex	1000 Mbps, Full-duplex	1000 Mbps, Full-duplex	Assuming maximum capability of NIC is 1000 Mbps, full-duplex.
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 mismatch
100 Mbps, Full-duplex	AUTO	100 Mbps, Full-duplex	100 Mbps, Half-duplex	Duplex Mismatch 1
AUTO	100 Mbps, Full-duplex	100 Mbps, Half-duplex	100 Mbps, Full-duplex	Duplex Mismatch 1
100 Mbps, Full-duplex	100 Mbps, Full-duplex	100 Mbps, Full-duplex	100 Mbps, Full-duplex	Correct Manual Configuration2
100 Mbps, Half-duplex	AUTO	100 Mbps, Half-duplex	100 Mbps, Half-duplex	Link is established, but switch does not see any autonegotiation information from NIC and defaults to half-duplex when operating at 10/100 Mbps.
10 Mbps, Half-duplex	AUTO	10 Mbps, Half-duplex	10 Mbps, Half-duplex	Link is established, but switch does not see Fast Link Pulse (FLP) and defaults to 10 Mbps half-duplex.
10 Mbps, Half-duplex	100 Mbps, Half-duplex	No Link	No Link	Neither side establishes link, due to speed mismatch.
AUTO	100 Mbps, Half-duplex	100 Mbps, Half-duplex	100 Mbps, Half-duplex	Link is established, but NIC does not see any autonegotiation information and defaults to 100 Mbps, half-duplex.
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 10 Mbps, half-duplex.

其中，黃色代表最佳設定，橘色代表效能不好的設定，紅色代表完全不能使用的設定。