Chapter 4 TCP/IP Networking 4.1 – History of TCP/IP 4.2 – IP Addressing 4.3 – Name Resolution 4.4 – TCP/IP Protocols

History of TCP/IP

Origins and Growth of TCP/IP The U.S. Defense Department Advanced Research Projects Agency (DARPA) produced the designs and experimental networks that evolved into the public Internet. DARPA also accelerated the spread of Transmission Control Protocol /Internet Protocol (TCP/IP) by including it in distributions of the UNIX operating system.

Origins and Growth of TCP/IP

It took 38 years for radio to achieve what is called "universal service". Television is now taken for granted as a source of news and entertainment. It took 59 years to achieve "universal service”. The Internet has achieved most of its explosive growth within the past ten years and is now beginning to absorb elements of the telephone and television systems. No other technology can match this achievement.

The TCP/IP Network Model The TCP/IP network model closely resembles the OSI reference model and is the predominant protocol suite used in networking today. The TCP/IP network model contains four layers, unlike the OSI model, which contains seven layers.

The TCP/IP Network Model The application layer of the TCP/IP model defines many of the applications that are used in networks. It determines protocol and data syntax rules at the application level. Transfer Protocol (FTP), Trivial File Transfer Protocol (TFTP), Simple Mail Transfer Protocol (SMTP), Internet Message Access Protocol (IMAP), Post Office Protocol version 3 (POP3), Simple Network Management Protocol (SNMP), and Telnet.

The TCP/IP Network Model TCP/IP transport layer defines only Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). It provides reliability and flow control. Reliability is achieved through a sequence of acknowledgements that guarantee the delivery of each packet. Flow control is achieved through the windowing.

The TCP/IP Network Model Both TCP and UDP use port numbers to pass data to the upper layers. Port numbers help define and keep track of all the different types of conversations that are taking place throughout the network.

The TCP/IP Network Model The Internet layer of the TCP/IP model defines addressing and path selection. This is the same function as the network layer in the OSI model. Routers use Internet layer protocols to identify an appropriate path for data packets as they travel from network to network. Protocols defined at this layer are IP, Internet Control Message Protocol (ICMP), Address Resolution Protocol (ARP), and Reverse Address Resolution Protocol (RARP).

The TCP/IP Network Model IP provides the routers with the ability, or addressing, to move data to the desired destination. ICMP provides control and messaging capabilities, which are used when there is a problem somewhere in the network. ICMP is used to send a message back to the host, informing it that the destination host was unreachable and is also the basis for the ping and traceroute commands. ARP is used to find the MAC address of a host, switch, or router, when given its IP address. RARP is used when the MAC address of a host is known, but the IP address is not known.

The TCP/IP Network Model The network interface layer maps to the data link and physical layers of the OSI model. This layer defines TCP/IP- specific functions related to the preparation of data for transmission over the physical media, including addressing. It also specifies what types of media can be used for the data transmission.

TCP/IP and Network Operating Systems Today, all NOS vendors have adopted the TCP/IP protocol suite for carrying data between client and server systems. Although the older proprietary protocols remain in use, TCP/IP is the standard that is implemented by all the NOS vendors.

IP Addressing

IPv4 Addressing For any two systems to communicate, they must be able to identify and locate each other. IP addresses are used to locate other computer systems when data must travel and be forwarded by other network hardware Each computer in a TCP/IP network must be given at least one unique identifier, or address.

IPv4 Addressing Overview By using the network identifier, IP can deliver a packet to the destination network. Once the packet arrives at a router connected to the destination network, IP must then locate the particular point where the destination computer is connected to that network.

IPv4 Addressing Overview Every IP address has two parts. –One part identifies the network to which the system is connected –Second part identifies that particular system on the network This kind of address is called a hierarchical address, because it contains different levels and because of the fact that the address can be broken down into two parts, with each parts being used as an identifier.

IPv4 Addressing Overview Inside a computer, an IP address is stored as a 32- bit sequence of 1s and 0s. To make the IP address easier to use, it is usually written as four decimal numbers. separated by periods. Each part of the address is called an octet because it is made up of eight binary characters.

IPv4 Addressing Overview IP addresses are divided into classes to define the large (Class A), medium (Class B), and small (Class C) networks. Knowing the class of an IP address is the first step in determining which part of the address identifies the network and which part identifies the host.

Class A Addresses In a Class A address, the first number (octet) is the network portion, and the last three numbers are the host portion. The format is Network.Host.Host.Host, or N.H.H.H. Only is valid for Class A networks because network is reserved. The IP address is known as the "local loopback" address, and is used to test the NIC of the local system.

Class B Addresses A Class B IP address divides the network portion from the host portion between the second and third octet. The format is N.N.H.H. If the first octet in an IP address is greater than 127 but less than 192, it is a Class B address.

Class C Addresses A Class C IP address divides the network portion from the host portion between the third and fourth octet. The format is N.N.N.H. If the first octet of the IP address is greater than 191 but less than 224, it is a Class C address.

Class D and E Addresses Class D and Class E addresses are used for special purposes. Class D is reserved for a technique called multicast, and Class E addresses are used for experimental purposes. Commercial organizations use classes A, B, or C addresses to identify networks and hosts.

The IPv4 Address Crisis The Internet faced the situation where it appeared that growth would be limited or even stopped because the Internet address space could become exhausted. In response, Internet engineers developed a set of techniques to make more efficient use of the Internet address space. Among these techniques was the subnetting. Subnetting is the process of splitting a network portion of an IP address, which allows an administrator to partition or divide a network.

The IPv4 Address Crisis Subnetting takes the IP address, which is divided into a network portion and a host portion, and then divides it further by adding a third part, the subnet number. The result is an address that has the form network number, subnet number, and host number.

The IPv4 Address Crisis It is important to know the difference between private IP addressing and public IP addressing. They are private addresses because they are only known to the company administrator and not known to the public.

The IPv4 Address Crisis NAT enables companies to keep their private addresses secure and not known to the public. NAT is enabled on a router or a gateway device, which translates all of the incoming and outgoing traffic through the known, or public IP addresses. The Internal IP address is different and kept private from the external public address that is exposed to others through the Internet. The public IP addresses are what allow people within the company to access networks outside of the LAN.

IPv6 Internet Protocol version 6 (IPv6) is the next generation protocol designed to replace the current version of the Internet Protocol, IPv4. IPv6 fixes a number of problems in IPv4, such as the limited number of available IPv4 addresses. It will also add many improvements to IPv4 in routing and in various network configuration tasks. IPv6 is expected to gradually replace IPv4, with the two coexisting for a number of years during a transition period.

Subnetting Subnets are similar to the American telephone numbering system. It is divided into area codes, which are divided into exchanges, and further divided into individual connections. Subnet addresses specify a network number, a subnet number, within the network, and a host number within the subnet.

Subnetting It is important to know how many subnet/networks are needed and how many hosts will be allowed to be on that network. With subnetting, the network is not limited to the standard Class A, B, or C subnet masks and there is more flexibility in the network design.

Name Resolution

Overview of Name Resolution By their numerical form addresses are difficult to remember and to manage. This is true when there is a need to change addresses to adapt to changing network conditions. Names are easy to work with. The technique that allows names to represent network addresses is called name resolution.

Hostnames and Host Tables On the network, each computer is given a unique name to identify it. This name is used to communicate with a particular computer. To reach another computer, the network needs to use the IP address of that computer. Host tables are lists that can be configured in each computer, associating the names of the computers in the network with the IP address host table. The table includes the IP address and the name that is mapped to that address.

The Domain Name System Specialized servers within the network accomplish the work of translating names into addresses. The DNS works like directory assistance in the phone system. Using the phone system, a person's name and address may be known, but not their phone number. A call to the directory assistance produces the phone number that matches the name and address.

Name Services and the NOS In a NOS, user programs can access network devices and services by name. All NOSs use DNS to translate computer names into IP addresses.

WINS To resolve or map the NETBIOS names used by applications into IP addresses, Microsoft added Windows Internet Naming Service (WINS) as an extension to DNS. WINS automates the process of translating NETBIOS names into IP addresses so packets can be properly delivered to devices or services.

TCP/IP Protocols

Overview of TCP/IP protocols A protocol is a set of messages that is exchanged between systems in a defined sequence in order to accomplish a specific networking task. TCP/IP is a "suite" or collection of different protocols, each one performing a specialized task. In a well-functioning network, the individual protocols are coordinated so that, taken together, they deliver network services to application programs.

Address Resolution Protocol (ARP) The first system knows that the second is located somewhere on the network but does not know its exact location on the network. The source will broadcast an ARP request to find the MAC address of the intended destinations MAC address. The signal sent is a broadcast message and all the devices in the LAN will hear it. Only the destination device will respond to the ARP request.

Internet Control Message Protocol (ICMP) ICMP provides a set of error and control messages to help track and resolve network problems. ICMP is used to send a “destination unreachable” message when there is an error somewhere in the network that is preventing the frame or packet from being forwarded to the destination device.

Internet Control Message Protocol (ICMP) It includes a type of message, called an Echo Request, which can be sent from one host to another to see if it is reachable on the network. If it is reachable, the destination host will reply with the ICMP Echo Reply message. The Ping program uses ICMP to send Echo Request messages and to receive the Echo Reply messages. An ICMP echo-request is generated by the Ping command.

Transmission Control Protocol (TCP) The Transmission Control Protocol (TCP) has the job of guaranteeing that messages arrive at their destination, or if they cannot be delivered, informing the application programs of the failure. Once a TCP connection is made between two applications, all the messages flow from the origin to the destination over that logical connection.

User Datagram Protocol (UDP) User Datagram Protocol (UDP) provides an "unreliable" service to applications that can tolerate a loss of some messages but still function. Streams of video or audio data fall into this category. UDP is: –fast –unreliable –assumes applications will retransmit on error –often use diskless workstations

DHCP Services Dynamic Host Configuration Protocol (DHCP) enables computers on an IP network to extract their configurations from a DHCP server. When a computer on the network needs an IP address, it sends a request to a DHCP server. The DHCP server can then provide the host computer with all the configuration information it needs.

Hypertext Transport Protocol (HTTP) The Hypertext Transport Protocol (HTTP) transfers World Wide Web pages between web browser client programs like Netscape Communicator or Internet Explorer, and web servers where web pages are stored. HTTP defines the exact format of the requests that the browser sends as well as the format of the replies that the server returns.

File Transfer Protocol (FTP) FTP is a general-purpose protocol that can be used to copy all types of files from one computer to another. FTP makes use of the TCP reliable transport services to establish a logical connection between the systems. FTP is one of the most heavily used protocols on the Internet.

Telnet Telnet enables interactive terminal communications with remote systems as if they were directly connected to the terminal, even though there may be many networks separating the terminal from the remote system. Users can type commands to the system as if they were directly connected to it.

SMTP Simple Mail Transfer Protocol (SMTP) is a protocol for sending messages between servers. The messages can then be retrieved with an client using either Post Office Protocol (POP) or Internet Message Access Protocol (IMAP).

POP3 Post Office Protocol version 3 (POP3) is a common mail service protocol that is used by ISPs that provide Internet and service to home customers. POP3 permits a workstation to retrieve mail that the server is holding.

IMAP Internet Message Access Protocol (IMAP) is a newer e- mail protocol that is more robust than POP3. It is a method for accessing electronic mail or bulletin board messages that are kept on a mail server. It is fully compatible with Multipurpose Internet Mail Extension (MIME) Internet messaging standards, and it allows message access and management from more than one computer.