Simplified header format. IPv6 has a fixed length header, which does not include most of the options an IPv4 header can include. Even though the IPv6 header contains two 128 bit addresses (source and destination IP address) the whole header has a fixed length of 40 bytes only. This allows for faster processing. Options are dealt with in extension headers, which are only inserted after the IPv6 header if needed. So for instance if a packet needs to be fragmented, the fragmentation header is inserted after the IPv6 header. The basic set of extension headers is defined in RFC 2460.
next header
IPv6 includes an improved option mechanism over IPv4. IPv6 options are placed in separate extension headers that are located between the IPv6 header and the transport-layer header in a packet. Most IPv6 extension headers are not examined or processed by any router along a packet's delivery path until it arrives at its final destination. This facilitates a major improvement in router performance for packets containing options
cookie
Frame Header - Network Header - Transport Header - Data - Frame Trailer
By configuring an IPv6 Unicast routing command on a router you are allowing the router to communicate with the IPv6 interface. This is needed if you intend to send or receive data over an IPv6 network.
SPI field
It reads the protocol/bit stream/header
data link header
Example of a stream cipher
header, packet(data), and trailer
Virtual Private Network (VPN)