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IPv6 header

IPV6

  • An IPv6 packet has two parts: a header and a payload.

IPv6 header

The header consists of a fixed portion with minimal functionality required for all packets and may be followed by optional extensions to implement particular features. The fixed header occupies the first 40 octets (320 bits) of the IPv6 packet.

An IPv6 Header Contains the Following Components: - Version(4-bits)     - Indicates the version of Internet Protocol, which contains bit sequence 0110. - Traffic Class(8-bits)     The Traffic Class field indicates the class or priority of an IPv6 packet, similar to the Service Field in an IPv4 packet. It helps routers handle traffic based on the priority of the packet. - Flow Label (20-bits)     The Flow Label field is used by a source to label the packets belonging to the same flow and request special handling by intermediate IPv6 routers, such as non-default quality of service or real-time service. - Payload Length (16-bits)     - It is a 16-bit field that indicates the total size of the payload, which tells routers about the amount of information a particular packet contains in its payload. - Next Header (8-bits)     The Next Header indicates the type of extension header immediately following the IPv6 header. In some cases, it indicates the protocols contained within upper-layer packets, such as TCP and UDP. - Hop Limit (8-bits)     The hop Limit field is the same as TTL in IPv4 packets. It indicates the maximum number of intermediate nodes an IPv6 packet is allowed to travel. - Source  Address (128-bits)     - Source Address is the 128-bit IPv6 address of the packet's source. - Destination Address (128-bits)     The destination Address field indicates the IPv6 address of the final destination(in most cases). All the intermediate nodes can use this information to correctly route the packet.

Extension Headers

To rectify the limitations of the IPv4 Option Field, Extension Headers are introduced in IP version 6. The extension header mechanism is an essential part of the IPv6 architecture. The next Header field of an IPv6 fixed header points to the first Extension Header, and this first extension header points to the second extension header, and so on.

EXTheader

The IPv6 packets may contain zero, one, or more extension headers, but these should be in their recommended order.

nxtheader