Protocol Tutorial

Ethernet II Header Format

Guide to Ethernet II frame structure: preamble, SFD, destination MAC address, source MAC address, EtherType, payload, and FCS. Understand data link layer framing.

Protocol Overview

Ethernet II Frame Format (IEEE 802.3)

Header Size: 14 bytes (112 bits)
Fields: 3
Endianness: big
Spec: IEEE 802.3

Header Fields

FieldOffsetSizeTypeDescription
Destination MAC
dest_mac
0 bits48 bitsuint64macDestination MAC address (6 bytes)
Source MAC
source_mac
48 bits48 bitsuint64macSource MAC address (6 bytes)
EtherType
ethertype
96 bits16 bitsuint16hexProtocol type of payload
Known values: 2048=IPv4 (0x0800), 2054=ARP (0x0806), 33024=802.1Q VLAN (0x8100), 34525=IPv6 (0x86DD)

Common Ethernet Mistakes

  • 1Confusing Ethernet II (EtherType ≥ 1536) with IEEE 802.3 (Length ≤ 1500)
  • 2Forgetting that MAC addresses are 48 bits (6 bytes), not 32 or 64
  • 3Misreading byte order: MAC addresses are typically shown in big-endian (network order)
  • 4Not accounting for the 4-byte FCS (Frame Check Sequence) at the end
  • 5Assuming all frames have a payload (minimum frame size is 64 bytes including FCS)

Try It Yourself

Parse real Ethernet II packets in the interactive visualizer

Open Visualizer

Related Resources

Ethernet Frame Parser - Decode Ethernet II Frames Online | ByteLensEthernet II Basic Frame Example - ByteLens

Quick Facts

ProtocolEthernet II
Header Size14 bytes
Fields3
Endiannessbig
SpecificationIEEE 802.3