DIX Ethernet Frame Format

 

Preamble The alternating pattern of ones and zeros tells receiving stations that a frame is coming (Ethernet or IEEE 802.3). The Ethernet frame includes an additional byte that is the equivalent of the Start of Frame (SOF) field specified in the IEEE 802.3 frame.

Destination and Source Addresses The first 3 bytes of the addresses are specified by the IEEE on a vendor-dependent basis. The last 3 bytes are specified by the Ethernet or IEEE 802.3 vendor. The source address is always a unicast (single-node) address. The destination address can be unicast, multicast (group), or broadcast (all nodes).

Type (Ethernet) The type specifies the upper-layer protocol to receive the data after Ethernet processing is completed.

Data (Ethernet) After physical-layer and link-layer processing is complete, the data contained in the frame is sent to an upper-layer protocol, which is identified in the Type field. Although Ethernet Version 2 does not specify any padding (in contrast to IEEE 802.3), Ethernet expects at least 46 bytes of data.

Frame Check Sequence (FCS) This sequence contains a 4-byte cyclic redundancy check (CRC) value, which is created by the sending device and is recalculated by the receiving device to check for damaged frames.