How do Ethernet II frames differ from 802.3 frames with LLC?

• A. Ethernet II frames use a Length field and an LLC header.
• B. Ethernet II uses a Type field to indicate the protocol; 802.3 with LLC uses a Length field and an LLC header.
• C. Ethernet II frames require an LLC header; 802.3 frames do not.
• D. Ethernet II uses a Type field, and 802.3 frames always include an IP header.

Answer: (B)

The key idea is how the frame identifies the next protocol. In Ethernet II, the field that appears after the source MAC is EtherType, which directly indicates the upper-layer protocol (for example, 0x0800 means IPv4, 0x0806 means ARP). That lets devices immediately know how to interpret the payload without an LLC header.

In contrast, 802.3 frames that use the LLC sublayer have a Length field after the source MAC, not EtherType. The payload begins with an LLC header (and often a SNAP header) that describes the protocol via DSAP/SSAP and control fields. So the protocol isn’t signaled by a dedicated EtherType value, but by the LLC/SNAP information that follows.

That’s why the correct description is that Ethernet II uses a Type field to indicate the protocol, while 802.3 with LLC uses a Length field and an LLC header. The other statements misstate which field is used or add requirements that don’t hold (for example, Ethernet II does not require an LLC header, and 802.3 with LLC does not imply that IP must always be present).