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_____________________________________________________ / Oblivion Underground Magazine \ / Issue 2 15/04/2000 \ ▌ History, Present and Future of TCP/IP ▌ \ by Slider / \_____________________________________________________/ - SOF - Introduction to TCP/IP - History, Present and the Future. Today, the Internet, World Wide Web, and Information Super Highway are familiar terms to millions of people all over the world. Transmission Control Protocol/Internet Protocol (TCP/IP) is the protocol suite developed for the Internet. In this file I describe how the Internet was formed, how it developed and how it is likely to develop in the future. - Internet History - Where It All Came From Networks have become a fundamental, if not the most important, part of today's information systems. They form the backbone for information sharing in enterprises, governmental and scientific groups. That information can take several forms. It can be notes and documents, data to be processed by another computer, files sent to colleagues, and even more exotic forms of data. Most of these networks were installed in the late 60s and 70s, when network design was the "state of the art" topic of computer research and sophisticated implementers. It resulted in multiple networking models such as packet-switching technology, collision-detection local area networks, hierarchical enterprise networks, and many other excellent technologies. From the early 70s on, another aspect of networking became important: protocol layering, which allows applications to communicate with each other. A complete range of architectural models were proposed and implemented by various research teams and computer manufacturers. The result of all this great know-how is that today any group of users can find a physical network and an architectural model suitable for their specific needs. This ranges from cheap asynchronous lines with no other error recovery than a bit-per-bit parity function, through full-function wide area networks (public or private) with reliable protocols such as public packet-switching networks or private SNA networks, to high-speed but limited-distance local area networks. The down side of this exploding information sharing is the rather painful situation when one group of users wants to extend its information system to another group of users who happen to have a different network technology and different network protocols. As a result, even if they could agree on a type of network technology to physically interconnect the two locations, their applications (such as mailing systems) still would not be able to communicate with each other because of the different protocols. This situation was recognized rather early (beginning of the 70s) by a group of researchers in the U.S. who came up with a new principle: internetworking. Other official organizations became involved in this area of interconnecting networks, such as ITU-T (formerly CCITT) and ISO. All were trying to define a set of protocols, layered in a well-defined suite, so that applications would be able to talk to other applications, regardless of the underlying network technology and the operating systems where those applications run. - Internetworks Those original designers, funded by the Defense Advanced Research Projects Agency (DARPA), of the ARPANET protocol suite introduced fundamental concepts such as layering and virtualizing in the world of networking, well before ISO even took an interest in networking. The official organization of those researchers was the ARPANET Network Working Group, which had its last general meeting in October 1971. DARPA continued its research for an internetworking protocol suite, from the early NCP (Network Control Program) host-to-host protocol to the TCP/IP protocol suite, which took its current form around 1978. At that time, DARPA was well known for its pioneering of packet-switching over radio networks and satellite channels. The first real implementations of the Internet were found around 1980 when DARPA started converting the machines of its research network (ARPANET) to use the new TCP/IP protocols. In 1983, the transition was completed and DARPA demanded that all computers willing to connect to its ARPANET use TCP/IP. DARPA also contracted Bolt, Beranek, and Newman (BBN) to develop an implementation of the TCP/IP protocols for Berkeley UNIX on the VAX and funded the University of California at Berkeley to distribute that code free of charge with their UNIX operating system. The first release of the Berkeley Software Distribution to include the TCP/IP protocol set was made available in 1983 (4.2BSD). From that point on, TCP/IP spread rapidly among universities and research centers and has become the standard communications subsystem for all UNIX connectivity. The second release (4.3BSD) was distributed in 1986, with updates in 1988 (4.3BSD Tahoe) and 1990 (4.3BSD Reno). 4.4BSD was released in 1993. Due to funding constraints, 4.4BSD was the last release of the BSD by the Computer Systems Research Group of the University of California at Berkeley. As TCP/IP internetworking spread rapidly, new wide area networks were created in the U.S. and connected to ARPANET. In turn, other networks in the rest of the world, not necessarily based on the TCP/IP protocols, were added to the set of interconnected networks. The result is what is described as The Internet. Some examples of the different networks that have played key roles in this development are described in the next sections. - The Internet What exactly is the Internet? First, the word internet (also internetwork) is simply a contraction of the phrase interconnected network. However, when written with a capital *I* the Internet refers to a worldwide set of interconnected networks, so the Internet is an internet, but the reverse does not apply. The Internet is sometimes called the connected Internet. The Internet consists of the following groups of networks (see the following sections for more information on some of these): * Backbones: large networks that exist primarily to interconnect other networks. Currently the backbones are NSFNET in the US, EBONE in Europe, and large commercial backbones. * Regional networks connecting, for example, universities and colleges. * Commercial networks providing access to the backbones to subscribers, and networks owned by commercial organizations for internal use that also have connections to the Internet. * Local networks, such as campus-wide university networks. In many cases, particularly for commercial, military and government networks, traffic between these networks and the rest of the Internet is restricted. - ARPANET Sometimes referred to as the *grand-daddy of packet networks*, the ARPANET was built by DARPA (which was called ARPA at that time) in the late 60s to accommodate research equipment on packet-switching technology and to allow resource sharing for the Department of Defense's contractors. The network interconnected research centers, some military bases and government locations. It soon became popular with researchers for collaboration through electronic mail and other services. It was developed into a research utility run by the Defense Communications Agency (DCA) by the end of 1975 and split in 1983 into MILNET for interconnection of military sites and ARPANET for interconnection of research sites. This formed the beginning of the *capital I* Internet. In 1974, the ARPANET was based on 56 Kbps leased lines that interconnected packet-switching nodes (PSN) scattered across the continental U.S. and western Europe. These were minicomputers running a protocol known as 1822 (after the number of a report describing it) and dedicated to the packet-switching task. Each PSN had at least two connections to other PSNs (to allow alternate routing in case of circuit failure) and up to 22 ports for user computer (host) connections. These 1822 systems offered reliable, flow-controlled delivery of a packet to a destination node. This is the reason why the original NCP protocol was a rather simple protocol. It was replaced by the TCP/IP protocols, which do not assume reliability of the underlying network hardware and can be used on other-than-1822 networks. This 1822 protocol did not become an industry standard, so DARPA decided later to replace the 1822 packet switching technology with the CCITT X.25 standard. Data traffic rapidly exceeded the capacity of the 56 Kbps lines that made up the network, which were no longer able to support the necessary throughput. Today the ARPANET has been replaced by new technologies in its role of backbone on the research side of the connected Internet (see NSFNET later in this chapter), whereas MILNET continues to form the backbone of the military side. - NSFNET NSFNET, the National Science Foundation Network, is a three-level internetwork in the United States consisting of: * The backbone: a network that connects separately administered and operated mid-level networks and NSF-funded supercomputer centers. The backbone also has transcontinental links to other networks such as EBONE, the European IP backbone network. * Mid-level networks: of three kinds (regional, discipline-based and supercomputer consortium networks). * Campus networks: whether academic or commercial, connected to the mid-level networks. First Backbone Originally established by the National Science Foundation (NSF) as a communications network for researchers and scientists to access the NSF supercomputers, the first NSFNET backbone used six DEC LSI/11 microcomputers as packet switches, interconnected by 56 Kbps leased lines. A primary interconnection between the NSFNET backbone and the ARPANET existed at Carnegie Mellon, which allowed routing of datagrams between users connected to each of those networks. Second Backbone The need for a new backbone appeared in 1987, when the first one became overloaded within a few months (estimated growth at that time was 100% per year). The NSF and MERIT, Inc., a computer network consortium of eight state-supported universities in Michigan, agreed to develop and manage a new, higher-speed backbone with greater transmission and switching capacities. To manage it they defined the Information Services (IS) which is comprised of an Information Center and a Technical Support Group. The Information Center is responsible for information dissemination, information resource management and electronic communication. The Technical Support Group provides support directly to the field. The purpose of this is to provide an integrated information system with easy-to-use-and-manage interfaces accessible from any point in the network supported by a full set of training services. Merit and NSF conducted this project in partnership with IBM and MCI. IBM provided the software, packet-switching and network-management equipment, while MCI provided the long-distance transport facilities. Installed in 1988, the new network initially used 448 Kbps leased circuits to interconnect 13 nodal switching systems (NSS) supplied by IBM. Each NSS was composed of nine IBM RISC systems (running an IBM version of 4.3BSD UNIX) loosely coupled via two IBM Token-Ring Networks (for redundancy). One Integrated Digital Network Exchange (IDNX) supplied by IBM was individual at each of the 13 locations, to provide: * Dynamic alternate routing * Dynamic bandwidth allocation Third Backbone In 1989, the NSFNET backbone circuits topology was reconfigured after traffic measurements and the speed of the leased lines increased to T1 (1.544 Mbps) using primarily fiber optics. Due to the constantly increasing need for improved packet switching and transmission capacities, three NSSs were added to the backbone and the link speed was upgraded. The migration of the NSFNET backbone from T1 to T3 (45Mbps) was completed in late 1992. The subsequent migration to gigabit levels has already started and will continue through the late 1990s. In April 1995 the US government discontinued its funding of NSFNET. This was in part a reaction to growing commercial use of the network. About the same time, NSFNET gradually migrated the main backbone traffic in the U.S. to commercial network service providers, and NSFNET reverted to being a network for the research community. The main backbone network is now run in cooperation with MCI and is known as the vBNS (very high speed Backbone Network Service). NSFNET has played a key role in the development of the Internet. However, many other networks have also played their part and/or also make up a part of the Internet today. - Commercial Use of the Internet In recent years the Internet has grown in size and range at a greater rate than anyone could have predicted. A number of key factors have influenced this growth. Some of the most significant milestones have been the free distribution of Gopher in 1991, the first posting, also in 1991, of the specification for hypertext and, in 1993, the release of Mosaic, the first graphics-based browser. Today the vast majority of the hosts now connected to the Internet are of a commercial nature. This is an area of potential and actual conflict with the initial aims of the Internet, which were to foster open communications between academic and research institutions. However, the continued growth in commercial use of the Internet is inevitable so it will be helpful to explain how this evolution is taking place. One important initiative to consider is that of the Acceptable Use Policy (AUP). The first of these policies was introduced in 1992 and applies to the use of NSFNET. A copy of this can be obtained at nic.merit.edu/nsfnet/acceptable.use.policy. At the heart of this AUP is a commitment "to support open research and education". Under "Unacceptable Uses" is a prohibition of "use for for-profit activities", unless covered by the General Principle or as a specifically acceptable use. However, in spite of this apparently restrictive stance the NSFNET was increasingly used for a broad range of activities, including many of a commercial nature, before reverting to its original objectives in 1995. The provision of an AUP is now commonplace among Internet Service Providers, although the AUP has generally evolved to be more suitable for commercial use. Some networks still provide services free of any AUP. Let us now focus on the Internet service providers who have been most active in introducing commercial uses to the Internet. Two worth mentioning are PSINet and UUNET, which began in the late 80s to offer Internet access to both businesses and individuals. The California-based CERFnet provided services free of any AUP. An organization to interconnect PSINet, UUNET and CERFnet was formed soon after, called the Commercial Internet Exchange (CIX), based on the understanding that the traffic of any member of one network may flow without restriction over the networks of the other members. As of July 1997, CIX had grown to more than 146 members from all over the world connecting member internets. At about the same time that CIX was formed, a non-profit company, Advance Network and Services (ANS), was formed by IBM, MCI and Merit, Inc. to operate T1 (subsequently T3) backbone connections for NSFNET. This group was active in increasing the commercial presence on the Internet. ANS formed a commercially oriented subsidiary called ANS CO+RE to provide linkage between commercial customers and the research and education domains. ANS CO+RE provides access to NSFNET as well as being linked to CIX. In 1995 ANS was acquired by America Online. In 1995, as the NSFNET was reverting to its previous academic role, the architecture of the Internet changed from having a single dominant backbone in the U.S. to having a number of commercially operated backbones. In order for the different backbones to be able to exchange data, the NSF set up four Network Access Points (NAPs) to serve as data interchange points between the backbone service providers. Another type of interchange is the Metropolitan Area Ethernet (MAE). Several MAEs have been set up by Metropolian Fiber Systems (MFS), who also have their own backbone network. NAPs and MAEs are also referred to as public exchange points (IXPs). Internet Service Providers (ISPs) typically will have connections to a number of IXPs for performance and backup. Similar to CIX in the United States, European Internet providers formed the RIPE (RΘseaux IP EuropΘens) organization to ensure technical and administrative coordination. RIPE was formed in 1989 to provide a uniform IP service to users throughout Europe. Currently, more than 1000 organizations participate in RIPE, and close to 6 million hosts (as of February 1998) could be reached via RIPE-coordinated networks. Today, the largest Internet backbones run at OC3 (155 Mbps) or OC12 (622 Mbps). By late 1998 OC12 should be the standard speed for major backbones. - Information Superhighway One recent and important initiative was the creation of the U.S. Advisory Council on the National Information Infrastructure (NIIAC) headed by U.S. Vice President Al Gore (who has been credited with coining the phrase *information superhighway*). The Advisory Council, which was made up of representatives from many areas of industry, government, entertainment and education, met for a period of two years from 1994-6. At the end of their term, they concluded their work with the publishing of two major reports: * Kickstart Initiative: Connecting America's Communities to the Information Superhighway * A Nation of Opportunity: Realizing the Promise of the Information Superhighway Among the findings in these reports are the goal that every person in the U.S. should have access to the Internet by the year 2005, with all schools and libraries being connected by the year 2000. Although the reports do not specify direct government funding for expansion of the Internet, preferring "commercial and competitive initiatives" to be the driving force, it does give a responsibility to all levels of government to ensure fair access and remove regulatory obstacles. The most recent and substantive government affirmation for the Internet came, in 1996, in the form of the Next Generation Internet initiative. This was launched by the Clinton administration with the goals of: * Connecting universities and national labs with networks that are 100-1000 times faster than today's (as of October 1996) Internet. * Promote expermentation with the next generation of networking technologies. * Demonstrate new applications that meet important national goals and missions. The initiative included funding of $100 million for 1998. - Internet2 The success of the Internet and the subsequent frequent congestion of the NSFNET and its commercial replacement led to some frustration among the research community who had previously enjoyed exclusive use of the Internet. The university community, therefore, together with government and industry partners, and encouraged by the funding component of the NGI, have formed the Internet2 project. Internet2 has the following principle objectives: * To create a high bandwidth, leading-edge network capability for the research community in the U.S. * To enable a new generation of applications and communication technologies to fully exploit the capabilities of broadband networks. * To rapidly transfer newly developed technologies to all levels of education and to the broader Internet community, both in the U.S. and abroad. - The Open Systems Interconnect (OSI) Model Around the same time that DARPA was researching for an internetworking protocol suite in response to the requirement for the establishment of networking standards, which eventually led to TCP/IP and the Internet, an alternative standards approach was being led by the CCITT (ComitΘ Consultatif International Telephonique et Telegraphique, or Consultative Committee on International Telephony and Telegraphy), and the ISO (International Organization for Standardization ). The CCITT has since become the ITU-T (International Telecommunications Union - Telecommunication Standardization Sector). This effort resulted in the OSI (Open Systems Interconnect) Reference Model (ISO 7498), which defined a seven-layer model of data communication with physical transport at the lower layer and application protocols at the upper layers. This model, is widely accepted as a basis for the understanding of how a network protocol stack should operate and as a reference tool for comparing network stack implementations. The OSI Reference Model has seven layers; each layer provides a set of functions to the layer above and, in turn, relies on the functions provided by the layer below. Although messages can only pass vertically through the stack from layer to layer, from a logical point of view, each layer communicates directly with its peer layer on other nodes. The seven layers are: Application Network applications such as terminal emulation and file transfer Presentation Formatting of data and encryption Session Establishment and maintenance of sessions Transport Provision of reliable and unreliable end-to-end delivery Network Packet delivery, including routing Data Link Framing of units of information and error checking Physical Transmission of bits on the physical hardware The two standards processes approach standardization from two different perspectives. The OSI approach started from a clean slate and defined standards, adhering tightly to their own model, using a formal committee process without requiring implementations. The Internet uses a less formal engineering approach, where anybody can propose and comment on RFCs, and implementations are required to verify feasibility. The OSI protocols developed slowly, and because running the full protocol stack is resource intensive, they have not been widely deployed, especially in the desktop and small computer market. In the meantime, TCP/IP and the Internet were developing rapidly and being put into use. - X.500: The Directory Service Standard The OSI protocols did, however, address issues important in large distributed systems that were developing in an ad hoc manner in the desktop and Internet marketplace. One such important area was directory services. The CCITT created the X.500 standard in 1988, which became ISO 9594, Data Communications Network Directory, Recommendations X.500-X.521 in 1990, though it is still commonly referred to as X.500. X.500 organizes directory entries in a hierarchical name space capable of supporting large amounts of information. It also defines powerful search capabilities to make retrieving information easier. Because of its functionality and scalability, X.500 is often used together with add-on modules for interoperation between incompatible directory services. X.500 specifies that communication between the directory client and the directory server uses the Directory Access Protocol (DAP). - The IP Address Exhaustion Problem The number of networks on the Internet has been approximately doubling annually for a number of years. However, the usage of the Class A, B and C networks differs greatly. Nearly all of the new networks assigned in the late 1980s were Class B, and in 1990 it became apparent that if this trend continued, the last Class B network number would be assigned during 1994. On the other hand, Class C networks were hardly being used. The reason for this trend was that most potential users found a Class B network to be large enough for their anticipated needs, since it accommodates up to 65534 hosts, whereas a class C network, with a maximum of 254 hosts, severely restricts the potential growth of even a small initial network. Furthermore, most of the class B networks being assigned were small ones. There are relatively few networks that would need as many as 65,534 host addresses, but very few for which 254 hosts would be an adequate limit. In summary, although the Class A, Class B and Class C divisions of the IP address are logical and easy-to-use (because they occur on byte boundaries), with hindsight they are not the most practical because Class C networks are too small to be useful for most organizations while Class B networks are too large to be densely populated by any but the largest organizations. In May 1996, there were all of Class A addresses either allocated or assigned, as well as 61.95 percent of Class B and 36.44 percent of Class C IP network addresses. The terms assigned and allocated in this context have the following meanings: Assigned The number of network numbers in use. The Class C figures are somewhat inaccurate, because the figures do not include many class C networks in Europe, which were allocated to RIPE and subsequently assigned but which are still recorded as allocated. Allocated This includes all of the assigned networks and additionally, those networks that have either been reserved by IANA (for example, the 63 class A networks are all reserved by IANA) or have been allocated to regional registries by IANA and will subsequently be assigned by those registries. Another way to look at these numbers is to examine the proportion of the address space that has been used. The figures in the table do not show for example that the Class A address space is as big as the rest combined, or that a single Class A network can theoretically have as many hosts as 66,000 Class C networks. Since 1990, the number of assigned Class B networks has been increasing at a much lower rate than the total number of assigned networks and the anticipated exhaustion of the Class B network numbers has not yet occurred. The reason for this is that the policies of the InterNIC on network number allocation were changed in late 1990 to preserve the existing address space, in particular to avert the exhaustion of the Class B address space. The new policies can be summarized as follows. - The upper half of the Class A address space (network numbers 64 to 127) is reserved indefinitely to allow for the possibility of using it for transition to a new numbering scheme. - Class B networks are only assigned to organizations that can clearly demonstrate a need for them. The same is, of course, true for Class A networks. The requirements for Class B networks are that the requesting organization: * Has a subnetting plan that documents more than 32 subnets within its organizational network * Has more than 4096 hosts Any requirements for a Class A network would be handled on an individual case basis. * Organizations that do not fulfill the requirements for a Class B network are assigned a consecutively numbered block of Class C network numbers. * The lower half of the Class C address space (network numbers 192.0.0 through 207.255.255) is divided into eight blocks, which are allocated to regional authorities as follows: 192.0.0 - 193.255.255 Multi-regional 194.0.0 - 195.255.255 Europe 196.0.0 - 197.255.255 Others 198.0.0 - 199.255.255 North America 200.0.0 - 201.255.255 Central and South America 202.0.0 - 203.255.255 Pacific Rim 204.0.0 - 205.255.255 Others 206.0.0 - 207.255.255 Others The ranges defined as Others are to be where flexibility outside the constraints of regional boundaries is required. The range defined as multi-regional includes the Class C networks that were assigned before this new scheme was adopted. The 192 networks were assigned by the InterNIC and the 193 networks were previously allocated to RIPE in Europe. The upper half of the Class C address space (208.0.0 to 223.255.255) remains unassigned and unallocated. * Where an organization has a range of class C network numbers, the range provided is assigned as a bit-wise contiguous range of network numbers, and the number of networks in the range is a power of 2. That is, all IP addresses in the range have a common prefix, and every address with that prefix is within the range. For example, a European organization requiring 1500 IP addresses would be assigned eight Class C network numbers (2048 IP addresses) from the number space reserved for European networks (194.0.0 through 195.255.255) and the first of these network numbers would be divisible by eight. A range of addresses satisfying these rules would be 194.32.136 through 194.32.143, in which case the range would consist of all of the IP addresses with the 21-bit prefix 194.32.136, or B'110000100010000010001'. The maximum number of network numbers assigned contiguously is 64, corresponding to a prefix of 18 bits. An organization requiring more than 4096 addresses but less than 16,384 addresses can request either a Class B or a range of Class C addresses. In general, the number of Class C networks assigned is the minimum required to provide the necessary number of IP addresses for the organization on the basis of a two-year outlook. However, in some cases, an organization can request multiple networks to be treated separately. For example, an organization with 600 hosts would normally be assigned four class C networks. However, if those hosts were distributed across 10 token-ring LANs with between 50 and 70 hosts per LAN, such an allocation would cause serious problems, since the organization would have to find 10 subnets within a 10-bit local address range. This would mean at least some of the LANs having a subnet mask of 255.255.255.192 which allows only 62 hosts per LAN. The intent of the rules is not to force the organization into complex subnetting of small networks, and the organization should request 10 different Class C numbers, one for each LAN. The use of Class C network numbers in this way has averted the exhaustion of the Class B address space, but it is not a permanent term solution to the overall address space constraints that are fundamental to IP. A long-term solution is needed and its called IP Version 6. But, this will be included in a later text for Oblivion Mag. Slider. - EOF - Shouts : Anyone that knows me.