IPv6 Header Format
Internet Protocol v6 address:
Internet Protocol version 6 (IPv6) is also known as Internet Protocol next generation (IPng). It also accommodates more features to meet the global requirement of the growing Internet.
To allocate a sufficient number of network addresses, IPv6 allows 128 bits of IP address separated into 8 sections of 2 bytes each. Unlike IPv4 where the address is represented as dotted-decimal notation, IPv6 uses hexadecimal numbers, and the colon (“:”) is used as a delimiter between the sections.
Version: This field is 4 bits long and it defines the version of the IP packet. The value of it for IPv6 is 6 and for IPv4 its value is 4. During the transition period from IPv4 to IPv6, the routers will be able to distinguish the two versions of the IP packets.
Traffic Class: This field is 20 bits long and it is used to distinguish between the different requirements for real-time delivery services.
Flow Label: This field is 20 bits long and it is used to allow the source and destination nodes to set up a pseudo connection with particular properties and requirements. It is designed to provide special handling of a particular flow of data.
Payload Length: It is 2 bytes in length and signifies the number of bytes that follow the 40 bytes base header. It is the length of the IP datagram excluding the base header.
Next Header: This field is of 1 bye length and it defines one of the extension headers that follow the base header. The extension headers also contain this field to indicate the next header. if this is the last IP header then the Next header field tells which of the transport protocols (TCP or UDP) the packet is to be passed.
Hop Limit: This field contains 1 byte and it signifies the maximum number of hops a packet can travel. The time to live field in the IPv4 header did the same task, except that in IPv4 it was counted in time and in IPv6 it is counted in terms of the number of routers.
Source Address: It is 16 bytes long and contains the IP address of the source machine to the network interface.
Destination Address: It is 16 bytes long and usually contains the IP address of the ultimate destination machine to the network interface. In the case of specific routing, it may contain the IP address of the next router.
Extension Header: Some of the fields Ipv4 that are missing in IPv6 are necessary in some of the cases. To handle this problem, IPv6 has introduced the concept of the extension header. There are be one or more of the six possible extension headers. These headers appear directly after the base header.