This chapter explains the structure of the IPv6 header and compares it to the IPv4 header. It also discusses Extension headers, which are new in IPv6.
Understanding the structure of a protocol header and the type of information that can be transported with it is the best foundation for working with a protocol. This understanding helps you to identify how the protocol can best be configured and what the options are. It also helps you to identify possible sources of problems and issues when troubleshooting.
The header structure of an IPv6 packet is specified in RFC 2460. The header has a fixed length of 40 bytes. The two fields for Source and Destination addresses each use 16 bytes (128 bits), so there are only 8 bytes for general header information. The IPv6 header is therefore much simpler and leaner than the IPv4 header, allowing for more efficient processing and, as we will see, more flexibility in extending the protocol to meet future needs.