IP and IPv6
For decades, the keystone of the TCP/IP protocol architecture has been the Internet Protocol (IP). Figure 5 part (a) shows the IP header format, which is a minimum of 20 octets, or 160 bits. The header includes 32-bit source and destination addresses. The Header Checksum field is used to detect errors in the header to avoid misdelivery. The Protocol field indicates whether TCP, UDP, or some other higher-layer protocol is using IP. The Flags and Fragment Offset fields are used in the fragmentation and reassembly process.
In 1995, the Internet Engineering Task Force (IETF), which develops protocol standards for the Internet, issued a specification for a next-generation IP, known then as IPng. This specification was turned into a standard in 1996 known as IPv6. IPv6 provides a number of functional enhancements over the existing IP, designed to accommodate the higher speeds of today's networks and the mix of data streams, including graphic and video, that are becoming more prevalent. But the driving force behind the development of the new protocol was the need for more addresses. The current IP uses a 32-bit address to specify a source or destination. With the explosive growth of the Internet and of private networks attached to the Internet, this address length became insufficient to accommodate all of the systems needing addresses. As Figure 5 part (b) shows, IPv6 includes 128-bit source and destination address fields.
Figure 5 IP headers.
Ultimately, all of the installations using TCP/IP are expected to migrate from the current IP to IPv6, but this process will take many years, if not decades.