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ICMPv6 | IPv6 address | IPv6 header |
IPv6 header

The IPv6 header has been created simpler than the IPv4 header. Several fields have been removed or renamed. The following fields are defined in IPv6:
  • Version: the 4 bits version field must be equal to 6 for IPv6
  • Traffic Class: is used for Quality of Service (QoS). Traffic classes with different QoS requirements can be distinguished in the network
  • Flow Label: identifies an end-to-end flow. This field is used for QoS purposes
  • Payload Length: this is 16 bit field gives the length of the IPv6 payload in bytes
  • Next Header: this 8 bits field identifies the protocol to which the contents of this datagram will be delivered (e.g. TCP or UDP). The field uses the same values as the protocol field in IPv4
  • Hop Limit: the value of this 8 bit field is decremented by one in each router that forwards the datagram. If the hop limit reaches zero, the datagram is discarded. Hop limit replaces the TTL (Time To Live) field of IPv4
  • Source & Destination Address: to support IPv6 addresses the size of the fields has changed from 32 in IPv4 to 128 bits in IPv6
The application shows the differences between the IPv4 and the IPv6 header format. Starting with the IPv4 header, the IPv6 header is derived step-by-step. See it by yourself!