When two devices using auto-negotiation are connected at different capabilities, what is the outcome?

• A. They fail to negotiate and use 10 Mbps half duplex
• B. Each device operates at its own fastest speed
• C. They negotiate to the highest common speed and duplex
• D. The link remains undefined until manual configuration

Answer: (C)

Auto-negotiation lets two Ethernet interfaces determine the best operating parameters they can both support. Each side advertises its capabilities (speed and duplex), and they exchange this information to agree on the fastest common mode. So when two devices with different capabilities are connected, they don’t each run at their own maximum; they settle on the highest speed and duplex that both ends can handle. For example, if one side can do 100 Mbps full or half and the other can do 100 Mbps full and 10 Mbps, they will negotiate to 100 Mbps full duplex. If there’s no overlap at all, the link may fail to negotiate and require manual configuration, but in typical cases they choose the best common option.