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Gary C. Kessler
The only way to cope with the changes on the Internet the number of hosts, types of applications, and growing security concerns is to implement a new version of the Internet protocol to succeed IPv4. The IETF formed the IPng Working Group to define this transitional protocol, and the result was IPv6 designed as an evolution from IPv4, rather than as a radical change.
The Internet is historically linked to the ARPANET, the pioneering packet-switched network built for the U.S. Department of Defense in 1969. Starting with four nodes that year, the ARPANET slowly grew to encompass many systems across the US, and connected to hosts in Europe and Asia by the end of the 1970s. By the early 1980s, many regional and national networks across the globe started to become interconnected, and their common communications protocols were based on the TCP/IP suite. By the late 1980s, the number of host systems on these primarily academic and research networks could be counted in the hundreds or thousands. In addition, most of the traffic was supporting simple text-based applications, such as E-mail, file transfers, and login.
By the 1990s, however, users discovered the Internet and commercial use, previously prohibited or constrained on the Internet, was actively encouraged. Since the beginning of this decade, new host systems are being added to the Internet at rates of up to 10% per month, and the Internet has been doubling in size every 10-12 months for several years. By January 1997, there were more than 16 million hosts on the Internet, ranging from PC-class systems to supercomputers, on more than 100,000 networks worldwide.
The number of connected hosts is only one measure of the Internets growth. Another way to quantify the change, however, is in the changing applications. On todays Internet it is common to see hypermedia, audio, video, animation, and other types of traffic that were once thought to be anathema to a packet-switching environment. As the Internet provides better service support, new applications will spark even more growth and changing demographics. In addition, nomadic access has become a major issue with the increased use of laptop computers, and security concerns have grown as a result of the increased amount of sensitive information accessible via the Internet.
The IP was introduced in the ARPANET in the mid-1970s. The version of IP commonly used today is IPv4, described in RFC 791.
Although several protocol suites (including OSI) were proposed over the years to replace IPv4, none succeeded because of IPv4s large and continually growing installed base. Nevertheless, IPv4 was never intended for todays Internet in terms of the number of hosts, types of applications, or security concerns.
In the early 1990s, the IETF recognized that the only way to cope with these changes was to design a new version of IP to become the successor to IPv4. The IETF formed the IPng Working Group to define this transitional protocol, ensuring long-term compatibility between the current and new IP versions and support for current and emerging IP-based applications.
Work started on IPng in 1991 and several IPng proposals were subsequently drafted. The result of this effort was IPv6, described in RFCs 1883 to 1886; these four RFCs were officially entered into the Internet Standards Track in December 1995.
IPv6 is designed as an evolution from IPv4 rather than as a radical change. Useful features of IPv4 were carried over in IPv6 and less useful features were dropped. According to the IPv6 specification, the changes from IPv4 to IPv6 fall primarily into the following categories:
IPv6 also introduces and formalizes terminology that, in the IPv4 environment, are loosely defined, ill-defined, or undefined. The new and improved terminology includes:
The format of an IPv6 header is shown in Exhibit 1. Although IPv6 addresses are four times the size of IPv4 addresses, the basic IPv6 header is only twice the size of an IPv4 header, thus decreasing the impact of the larger address fields. The fields of the IPv6 header are:
Exhibit 1. IPv6 Header Format | |||
---|---|---|---|
Version | Priority | Flow Label | |
Payload Length | Next Header | Hop Limit | |
Source Address | |||
Destination Address |
Exhibit 2. Sample Values of Next Header Field | |
---|---|
Value | Contents of the next header |
1 | Internet Control Message Protocol (ICMP) |
6 | Transmission Control Protocol (TCP) |
17 | User Datagram Protocol (UDP) |
43 | Routing header |
44 | Fragment header |
58 | Internet Control Message Protocol version 6 (ICMPv6) |
59 | Nothing; this is the final header |
60 | Destination Options header |
89 | Open Shortest Path First (OSPF) |
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