Which statement best describes auto-negotiation on Ethernet links?

• A. It always selects 100 Mbps full duplex
• B. It enables devices to automatically configure speed and duplex to the best common settings
• C. It disables negotiation of duplex settings
• D. It requires manually setting speed first

Answer: (B)

Auto-negotiation lets two Ethernet devices advertise their supported speeds and duplex modes and then agree on the best common combination. The goal is to operate at the highest speed and most capable duplex that both ends can support. If both sides can do 100 Mbps full duplex, that’s what they’ll use; if one side can only do 10 Mbps or half duplex, they’ll settle on the highest common option, typically still preferring full duplex whenever possible. This mechanism avoids mismatches like one side using 100 Mbps full while the other uses 10 Mbps half.

It’s not fixed to 100 Mbps full duplex, and it doesn’t disable negotiation or require you to set speed manually first. Manual settings are only needed if auto-negotiation is disabled or overridden to force a specific configuration.