TABLE OF CONTENTS This chapter discusses the implications of the IPv6 extension headers, how they work, and how they differ from the IP option headers used with IPv4. Particular attention will be paid to the proper order and use of header extensions, as well as discussion of the use of jumbograms, hop-by-hop options, destination options, routing, and fragmentation headers.
The most important IPv6 options, the IP Security Protocol (IPsec) headers, have already been introduced in Chapter 6. The ESP and AH headers look the same, whether used in IPv4 or IPv6, but the way those headers are attached to the IP header differs significantly. This chapter introduces the concept of using extension headers to carry optional Internet-layer data information about handling packets at the Internet layer that is not always needed but often required for particular applications. Security headers provide one set of examples. Not all packets need to be authenticated or encrypted, but when nonrepudiation or privacy is required, packets must carry additional security information.
Rather than making the length of the IPv6 headers variable, depending on whether optional Internet-layer data must be carried along with the packet (as in IPv4), IPv6 optional data is carried in these supplementary extension headers that are inserted in the packet after the main IPv6 headers.
This chapter provides an introduction to the concept of extension headers, along with the following.
IPv6 extension header placement in the packet
IPv6 extension header ordering in the packet
IPv6 extension header format
IPv6...
