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Ethernet Frame Format

Unit: 3 Lesson: 1

grr ethernet packet header formatting

  • preamble
  • start frame delimiter
  • destination MAC address
  • source MAC address
  • EtherType
  • Payload
  • frame check sequence (error checking)

preamble & sfd

used for clock syncing and part of the CSMA/CD protocol for collision detection. preamble is just 8 bytes of alternating 1s and 0s, with the sfd being two 1s at the end

EtherType

two bytes to indicate what type of packet is being sent, 0x0800 for IPv4 and 0x86DD for IPv6.

packet type is only valid of the byte value is less than 0x0600 if not, then it's used to indicate the length of the packet frame

error checking

4 byte checksum thats either a CRC or something called a Frame Check Sequence (FCS)

big boi ethernet packets

ethernet frame has a standard max size of 1518 bytes, where each frame has an 18 byte header

  • 6 bytes source/destination MAC address
  • 4 byte error check
  • 2 byte ethertype upper size limit is referred to as the Maximum Transmission Unit (MTU)

jumbo frames are huge boi ethernet packets with a max size of 9216 bytes, but it requires every single node in the network to support these huge boi ethernet packets. you can toggle support for huge boi ethernet packets in the switch's UI or using terminal mtu [size|9216]

#Netplus

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