Ethernet Frame General Information

The Preamble + SFD (which is 8 bytes total, 7 bytes in the Preamble and 1 byte in the SFD) is usually not calculated whe
n counting bits in the Ethernet header

• So, instead of the Ethernet header being 26 bytes (Preamble + SFD + DST MAC + SRC MAC + Type/Length + CRC)
  • (8 + 6 + 6 + 2 + 4) = 26 bytes
• The actual size of the Ethernet header + trailer is 18 bytes (DST MAC + SRC MAC + Type/Length + CRC)
  • (6 + 6 + 2 + 4) = 18 bytes

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• The minimum size for an Ethernet frame (Header + Payload [Packet] + Trailer) is 64 bytes
  • 64 bytes – 18 bytes (header + trailer size) = 46 bytes
  • Therefore, the minimum payload (packet) size is 46 bytes
• If the payload is less than 46 bytes, padding bytes are added
  • ie. 34-byte payload packet + 12-byte padding = 46 bytes