At what layer does Ethernet operate and what are common LAN speeds?

• A. Physical layer; common speeds include 10 Mbps and 100 Mbps.
• B. Data Link layer; common speeds include 100 Mbps (Fast Ethernet), 1 Gbps (Gigabit), and 10 Gbps (10GBASE-T).
• C. Network layer; common speeds include 1000 Mbps and 10,000 Mbps.
• D. Transport layer; common speeds include 1 Gbps and 100 Gbps.

Answer: (B)

Ethernet operates at the Data Link layer, where data is organized into frames and MAC addresses control delivery on a local network. This layer handles how frames are formed, addressed, and placed onto the local medium, as well as how access to the shared medium is coordinated.

Common LAN speeds defined by Ethernet are 100 Mbps (Fast Ethernet), 1 Gbps (Gigabit Ethernet), and 10 Gbps (10GBASE-T). These speeds describe the data rate of the link between devices and are supported by Ethernet standards over copper or fiber cabling.

Note that the Physical layer covers the actual signaling and cabling, while the Network layer deals with IP addressing and routing, which is why the Data Link layer is the correct choice for describing Ethernet's main function and typical speeds.