Content Overview The Internet was developed to provide a communication network that could continue to function in wartime. Although the Internet has evolved in ways very different from those imagined by its architects, it is still based on the TCP/IP protocol suite. The design of TCP/IP is ideal for the decentralized and robust network that is the Internet. Many protocols used today were designed using the four-layer TCP/IP model. It is useful to know both the TCP/IP and OSI networking models. Each model offers its own structure for explaining how a network works but there is much overlap between the two. Without an understanding of both, a system administrator may not have sufficient insight into why a network functions the way it does. Any device on the Internet that wants to communicate with other Internet devices must have a unique identifier. The identifier is known as the IP address because routers use a layer three protocol, the IP protocol, to find the best route to that device. IPv4, the current version of IP, was designed before there was a large demand for addresses. Explosive growth of the Internet has threatened to deplete the supply of IP addresses. Subnetting, Network Address Translation (NAT) and private addressing are used to extend IP addressing without exhausting the supply. Another version of IP known as IPv6 improves on the current version providing a much larger address space, integrating or eliminating the methods used to work with the shortcomings of IPv4. In addition to the physical MAC address, each computer needs a unique IP address, sometimes called logical address, to be part of the Internet. There are several methods of assigning an IP address to a device. Some devices always have a static address, while others have a temporary address assigned to them every time they connect to the network. When a dynamically assigned IP address is needed, the device can obtain it using several methods. For efficient routing to occur between devices, other issues must be resolved. For example, duplicate IP addresses can stop efficient routing of data. Students completing this module should be able to:

Explain why the Internet was developed and how TCP/IP fits the design of the Internet.
List the four layers of the TCP/IP model.
Describe the functions of each layer of the TCP/IP model.
Compare the OSI model and the TCP/IP model.
Describe the function and structure of IP addresses.
Understand why subnetting is necessary.
Explain the difference between public and private addressing.
Understand the function of reserved IP addresses.
Explain the use of static and dynamic addressing for a device.
Understand how dynamic addressing can be done using RARP, BootP and DHCP.
Use ARP to obtain the MAC address to send a packet to another device.
Understand the issues related to addressing between networks.

Content 9.1 Introduction to TCP/IP 9.1.1 History and future of TCP/IP The U.S. Department of Defense (DoD) created the TCP/IP reference model because it wanted a network that could survive any conditions. To illustrate further, imagine a world, crossed by multiple cable runs, wires, microwaves, optical fibers, and satellite links. Then imagine a need for data to be transmitted without regard for the condition of any particular node or network. The DoD required reliable data transmission to any destination on the network under any circumstance. The creation of the TCP/IP model helped to solve this difficult design problem. The TCP/IP model has since become the standard on which the Internet is based. In reading about the layers of the TCP/IP model layers, keep in mind the original intent of the Internet. Remembering the intent will help reduce confusion. The TCP/IP model has four layers: the application layer, transport layer, Internet layer, and the network access layer. Some of the layers in the TCP/IP model have the same name as layers in the OSI model. It is critical not to confuse the layer functions of the two models because the layers include different functions in each model. The present version of TCP/IP was standardized in September of 1981. As shown in Figure , IPv4 addresses are 32 bits long, written in dotted decimal, and separated by periods. IPv6 addresses are 128 bits long, written in hexadecimal, and separated by colons. Colons separate 16-bit fields. Leading zeros can be omitted in each field as can be seen in the Figure where the field :0003: is written :3:. In 1992 the standardization of a new generation of IP, often called IPng, was supported by the Internet Engineering Task Force (IETF). IPng is now known as IPv6. IPv6 has not gained wide implementation, but it has been released by most vendors of networking equipment and will eventually become the dominant standard. Web Links History of the Internet http://www.itep.co.ae/itportal/english/ Content/EducationalCenter/ InternetConcepts/ history_future.asp

Content 9.1 Introduction to TCP/IP 9.1.2 Application layer The application layer of the TCP/IP model handles high-level protocols, issues of representation, encoding, and dialog control. The TCP/IP protocol suite combines all application related issues into one layer and assures this data is properly packaged before passing it on to the next layer. TCP/IP includes not only Internet and transport layer specifications, such as IP and TCP, but also specifications for common applications. TCP/IP has protocols to support file transfer, e-mail, and remote login, in addition to the following applications:

File Transfer Protocol (FTP) – FTP is a reliable, connection-oriented service that uses TCP to transfer files between systems that support FTP. It supports bi-directional binary file and ASCII file transfers.
Trivial File Transfer Protocol (TFTP) – TFTP is a connectionless service that uses the User Datagram Protocol (UDP). TFTP is used on the router to transfer configuration files and Cisco IOS images, and to transfer files between systems that support TFTP. It is useful in some LANs because it operates faster than FTP in a stable environment.
Network File System (NFS) – NFS is a distributed file system protocol suite developed by Sun Microsystems that allows file access to a remote storage device such as a hard disk across a network.
Simple Mail Transfer Protocol (SMTP) – SMTP administers the transmission of e-mail over computer networks. It does not provide support for transmission of data other than plaintext.
Terminal emulation (Telnet) – Telnet provides the capability to remotely access another computer. It enables a user to log in to an Internet host and execute commands. A Telnet client is referred to as a local host. A Telnet server is referred to as a remote host.
Simple Network Management Protocol (SNMP) – SNMP is a protocol that provides a way to monitor and control network devices, and to manage configurations, statistics collection, performance, and security.
Domain Name System (DNS) – DNS is a system used on the Internet for translating names of domains and their publicly advertised network nodes into IP addresses.

Interactive Media Activity Drag and Drop: The Application Layer After completing this activity, the student will be able to identify the protocols used in the application layer. Web Links Application Layer http://searchnetworking.techtarget.com/ sDefinition/ 0,,sid7_gci211579,00.html

Content 9.1 Introduction to TCP/IP 9.1.3 Transport layer The transport layer provides transport services from the source host to the destination host. The transport layer constitutes a logical connection between the endpoints of the network, the sending host and the receiving host. Transport protocols segment and reassemble upper-layer applications into the same data stream between endpoints. The transport layer