freeCodeCamp/guide/english/network-engineering/ipv6-header/index.md

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IPv6 Header

IPv6 Header Format

Below is the IPv6 header format according to RFC2460:

Image of IPv6 Header

Version [4-bits]
  • Internet Protocol (IP) version number (decimal 6, binary 0110)
Traffic Class [8-bits]
  • Identifies different classes or priorities of IPv6 packets
Flow Label [20-bits]
  • Services that require special handling can utilize this field (defaults to all 0's)
Payload Length [16-bits]
  • Specifies the size of the payload including extension headers. Value is measured in Octets (8-bit values)
Next Header [8-bits]
  • Specifies the type of the next header after the IPv6 header
Hop Limit [8-bits]
  • Number of hops before the packet is discarded
  • Value is decremented by each forwarding node in the network. When the value reaches 0, the packet is discarded
  • Maximum hops using 8-bits is 2^8 or 256 hops
Source Address [128-bits]
  • The IPv6 address of the device sending the packet
Destination Address [128-bits]
  • The IPv6 address of the device(s) destined to receive the packet
  • Destination may be more than one host/device when using Multicast/Anycast

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