Which statement describes the role of the LLC sublayer in Ethernet?

• A. The data link layer uses LLC to communicate with the upper layers of the protocol suite
• B. LLC is implemented only in hardware
• C. LLC provides the physical addressing for Ethernet
• D. LLC adds a second header to the frame

Answer: (A)

The main idea is that the LLC sublayer acts as the interface between the data link layer and the network layer, allowing multiple network-layer protocols to share the same link by using service access points to identify the upper-layer protocol. In Ethernet (IEEE 802.2), LLC sits between the MAC sublayer and the network layer and helps the receiver determine whether the payload should be delivered to IP, ARP, or another protocol by using DSAP/SSAP values. This is why the statement describing LLC as the mechanism the data link layer uses to communicate with upper-layer protocols is the best fit.

Remember that the MAC sublayer handles physical addressing (MAC addresses) and frame delimiting, and that LLC is not restricted to hardware-only implementations. Also, in many Ethernet deployments, EtherType in the MAC header is used instead of LLC for protocol identification, so LLC isn’t visible in every frame.