The IPv6 protocol evolved from years of operational experiences with the IPv4 protocol. In defining the IPv6 protocol, the networking industry and the IETF community tried to overcome real and perceived shortcomings of IPv4. A number of IETF RFCs cover currently defined capabilities of IPv6. Each RFC was defined after rigorous and long debate in the IETF. In this chapter we highlight some of the basics of IPv6 protocol, such as operations, addressing, and provisioning, all of which are important for engineers and architects who plan, design, and deploy IPv6 in access broadband networks. In this chapter we set the stage for technical deployment issues discussed in later chapters.
In this section we briefly review the differences and similarities between the IPv4 and IPv6 headers and discuss the rationale behind the changes introduced into IPv6. IPv6 has a fixed 40-byte header encompassing eight fields. A quick look at Figure 2.1 shows that the IPv6 header inherits some fields from IPv4. Also, some fields are simply renamed, whereas others have been eliminated and new one(s) added.
The following fields in the IPv6 header are passed on from IPv4, including their original functions.
Version This is a 4-bit field that contains (0110) to indicate IPv6 instead of (0100), which was used for the IPv4 version.
Source Address A 32-bit field for IPv4, this is now a 128-bit field, to represent the larger IPv6 source address. ...