The Ethernet II frame consists of seven fields:
| Preamble | Start Frame Delimiter | Destination MAC | Source MAC | Length or Type | Data | Frame Check Sequence |
|---|---|---|---|---|---|---|
| 7 bytes | 1 byte | 6 bytes | 6 bytes | 2 bytes | 46–1500 bytes | 4 bytes |
- PREAMBLE: synchronises the NIC with the incoming bits.
- START FRAME DELIMITER: tells the NIC that the actual frame starts after this (plus framing info).
- DESTINATION MAC ADDRESS: self-explanatory.
- SOURCE MAC ADDRESS: self-explanatory.
- LENGTH OR TYPE: length of the data (payload) – how many bytes are in the DATA portion; or type – whether the payload is IPv4 or IPv6.
- DATA: encapsulated data + protocol information.
- FRAME CHECK SEQUENCE (FCS): used by the receiving device for error-checking – detects errors in the transmission.