Ethernet Frame Format

Ethernet Frames

The original 10 Mbps Ethernet specification defined a simple frame format where each frame is composed of five fields.

0. The Ethernet frame starts with a preamble (not shown in the figure below) that’s used by the physical layer of the receiver to synchronise its clock with the sender’s clock.

1. The first field of the frame is the destination address. As this address is placed at the beginning of the frame, an Ethernet interface can quickly verify whether it’s the frame recipient and if not, cancel the processing of the arriving frame.

2. The second field is the source address. While the destination address can be either a unicast or a multicast/broadcast address, the source address must always be a unicast address.

3. The third field is a 16 bit integer that indicates which type of network layer packet is ...