2 © 2004, Cisco Systems, Inc. All rights reserved. IT Essentials I v. 3.1 Module 10 Networking Fundamentals

Module 10 Networking Fundamentals 10.1 – Introduction to PC Networking 10.2 – Types of Networks 10.3 – Adding a Network Interface Card (NIC) 10.4 – Physical Components of a Network 10.5 – LAN Architectures 10.6 – Networking Protocols and the OSI Model 10.7 – TCP/IP Utilities 10.8 – Connecting to the Internet

Introduction to PC Networking

Defining a Computer Network A computer network allows users to communicate with other users on the same network by transmitting data on the cables used to connect them. A computer network is defined as having two or more devices (such as workstations, printers, or servers) that are linked together for the purpose of sharing information, resources, or both.

Defining a Computer Network A network consists of many overlapping systems, such as cabling, addressing schemes, or applications. The layers work together to transmit and receive data. The Open Systems Interconnection (OSI) reference model, was created to define these multiple layers.

File, Print, and Application Services Computer networks offer file and print services. In networks, different computers take on specialized roles or functions. Once connected, one or more computers in the network can function as network file servers. The server is a repository for files that can be accessed and shared across the network by many users.

File, Print, and Application Services All network operating systems offer file and print services. Sharing information, collaborating on projects, and providing access to input and output devices are common services of computer networks.

Mail Services services work like the postal system, with one computer taking on the function of post office. The user account operates like a post office box, where mail is held for the user until it is picked up over the network by an client program running in the user system. The is sent from the client computer to the server, which acts as the post office. The server sends it to the address.

Directory and Name Services To enable users and systems on the network to find the services they require, computer networks make use of directories and name services.

Directory and Name Services Directory and name services make a network easier to use. After the initial setup of the directory or name service, this translation takes place transparently. In addition to their ease of use, they also make the network more flexible.

The Internet The Internet is a worldwide public network of networks, interconnecting thousands of smaller networks to form one large “web” of communication. The Internet functions like a highway to facilitate exchange between geographically separated users, organizations, and branches of companies.

The Internet The phrase “information superhighway” describes the benefit of the Internet to business and private communication. The Internet breaks down barriers of time and space, enabling the sharing of information around the globe almost instantaneously.

Network Administration The ongoing task of network administration is to maintain and adapt the network to changing conditions. Network administrator responsibilities include: –Setting up new user accounts and services –Monitoring network performance –Repairing network failures

Simplex, Half-Duplex, and Full-Duplex Transmission Simplex transmission is a single one-way baseband transmission. It is also called unidirectional because the signal travels in only one direction. An example of simplex transmission is the signal sent from the cable TV station to the home television.

Simplex, Half-Duplex, and Full-Duplex Transmission This means that only one side can transmit at a time. Two-way radios, such as Citizens Band (CB) and police/emergency communications mobile radios, work with half- duplex transmissions.

Simplex, Half-Duplex, and Full-Duplex Transmission Traffic can travel in both directions at the same time. A regular telephone conversation is an example of full-duplex communication. Both parties can talk at the same time, and the person talking on the other end can still be heard by the other party while they are talking.

Types of Networks

Overview By using local-area network (LAN) and wide-area network (WAN) technologies, many computers are interconnected to provide services to their users. In providing services, networked computers take on different roles or functions in relation to each other. Some types of applications require computers to function as equal partners. Other types of applications distribute work so that one computer functions to serve a number of others in an unequal relationship.

Peer-to-Peer Networks In a peer-to-peer network, the networked computers act as equal partners, or peers, to each other. As peers, each computer can take on the client function or the server function alternately.

Client/Server Networks In a client/server network arrangement, network services are located in a dedicated computer whose only function is to respond to the requests of clients. The server contains the file, print, application, security, and other services in a central computer that is continuously available to respond to client requests.

Local-Area Networks (LANs) A local-area network (LAN) can connect many computers in a relatively small geographical area such as a home, an office, or a campus. It allows users to access high bandwidth media like the Internet and allows users to share devices such as printers.

Local-Area Networks (LANs) The general shape or layout of a LAN is called its topology. Topology defines the structure of the network. This includes the physical topology which is the actual layout of the wire or media, and the logical topology which is how the media is accessed by the hosts.

Wide-Area Networks (WANs) A WAN, as the name implies, is designed to work over a larger area than a LAN. A WAN uses point-to-point or point to multipoint, serial communications lines. Point-to-point lines connect only two locations, one on each side of the line. Point-to-multipoint lines connect one location on one side of the line to multiple locations on the other side.

Wide-Area Networks (WANs) The following are some of the more common WAN technologies: –Modems –Integrated Services Digital Network (ISDN) –Digital subscriber line (DSL) –Frame Relay –Asynchronous Transfer Mode (ATM) –The T (US) and E (Europe) Carrier series (T1, E1, T3, E3, and so on) –Synchronous Optical Network (SONET)

Wide-Area Networks (WANs) Connections across WAN lines may be temporary or permanent. Telephone or dialup lines, might make a temporary connection to a remote network from a computer in a home or small office. In both temporary and permanent cases, computers that connect over wide area circuits must use a modem or channel service unit/data service unit (CSU/DSU) at each end of the connection.

Wide-Area Networks (WANs) The public telephone system, sometimes referred to as plain old telephone service (POTS), is a circuit-switched communications network. When a telephone call is placed in this type of network, only one physical path is used between the telephones for the duration of that call. This pathway is maintained for the exclusive use of the call, until the connection is ended and the telephone is hung up.

Wide-Area Networks (WANs) In a packet-switched network, each individual packet of data can take a different route and no dedicated pathway or circuit is established.

Adding a Network Interface Card (NIC)

What is a NIC? A network interface card (NIC) is a device that plugs into a motherboard and provides ports for the network cable connections. It is the computer interface with the LAN. The NIC communicates with the network through serial connections and communicates with the computer through parallel connections.

Setting the IP Address In a (TCP/IP)-based LAN, PCs use an IP address to identify each other. These addresses allow computers that are attached to the network to locate each other. IP addresses for hosts on a LAN can be assigned in two ways: 1.Manually assigned by the network administrator 2.Assigned by a Dynamic Host Configuration Protocol (DHCP) server

DHCP Servers The most common and efficient way for computers on a large network to obtain an IP address is through a Dynamic Host Configuration Protocol (DHCP) server. DHCP is a software utility that runs on a computer and is designed to assign IP addresses to PCs. When the DHCP server receives a request from a host, it selects IP address information from a set of predefined addresses that are stored in its database.

Default Gateway A computer located on one network segment that is trying to talk to another computer on a different segment sends the data through a default gateway. The default gateway is the “near side” interface of the router, the interface on the router to which the network segment or wire of the local computer is attached.

Domain Name System Most hosts are identified on the Internet by friendly computer names known as domain names. The Domain Name System (DNS) is used to translate computer names such as cisco.com to their corresponding unique IP address. The DNS server keeps records that map computer (host) names and their corresponding IP address. These record types are all combined in the DNS table.

Physical Components of a Network

Network Topologies The network topology defines the way in which computers, printers, and other devices are connected. A network topology describes the layout of the wire and devices as well as the paths used by data transmissions. Commonly referred to as a linear bus, all the devices on a bus topology are connected by one single cable.

Network Topologies The star topology is the most commonly used architecture in Ethernet LANs. When installed, the star topology resembles spokes in a bicycle wheel. Larger networks use the extended star topology. When used with network devices that filter frames or packets, like bridges, switches, and routers, this topology significantly reduces the traffic on the wires by sending packets only to the wires of the destination host.

Network Topologies A frame travels around the ring, stopping at each node. If a node wants to transmit data, it adds the data as well as the destination address to the frame. The frame then continues around the ring until it finds the destination node, which takes the data out of the frame. –Single ring – All the devices on the network share a single cable –Dual ring – The dual ring topology allows data to be sent in both directions although only one ring is used at a time.

Network Topologies The mesh topology connects all devices (nodes) to each other for redundancy and fault tolerance. It is used in WANs to interconnect LANs and for mission critical networks like those used by governments. Implementing the mesh topology is expensive and difficult.

Physical versus Logical Topology Networks have both a physical and logical topology: –Physical topology –the layout of the devices and media. –Logical topology – the paths that signals travel from one point on the network to another. –The way in which data accesses media and transmits packets across it.

Networking Media Networking media can be defined simply as the means by which signals (data) are sent from one computer to another (either by cable or wireless means). Coaxial cable is a copper-cored cable surrounded by a heavy shielding and is used to connect computers in a network. There are several types of coaxial cable, including thicknet, thinnet, RG-59 (standard cable for cable TV), and RG-6 (used in video distribution).

Networking Media Twisted-pair is a type of cabling that is used for telephone communications and most modern Ethernet networks. A pair of wires forms a circuit that can transmit data. The pairs are twisted to provide protection against crosstalk, the noise generated by adjacent pairs. There are two basic types, shielded twisted-pair (STP) and unshielded twisted-pair (UTP).

Networking Media UTP comes in several categories that are based on the number of wires and number of twists in those wires. Category 3 is the wiring used primarily for telephone connections. Category 5 and Category 5e are currently the most common Ethernet cables used.

Networking Media Fiber-optic cable is a networking medium capable of conducting modulated light transmissions. Fiber-optic refers to cabling that has a core of strands of glass or plastic (instead of copper), through which light pulses carry signals. Signals that represent data are converted into beams of light.

Networking Media If the cost of running cables is too high or computers need to be movable without being tethered to cables, wireless is an alternative method of connecting a LAN. Wireless networks use radio frequency (RF), laser, infrared (IR), and satellite/microwaves to carry signals from one computer to another without a permanent cable connection.

Common Networking Devices A hub is a device that is used to extend an Ethernet wire to allow more devices to communicate with each other. Hubs are most commonly used in Ethernet 10BASE-T or 100BASE-T networks, although there are other network architectures that use them.

Common Networking Devices Bridges connect network segments. The basic functionality of the bridge resides in its ability to make intelligent decisions about whether to pass signals on to the next segment of a network. A switch is a more sophisticated device than a bridge, although the basic function of the switch is deceptively simple. Ethernet switches are becoming popular connectivity solutions because they increase network performance.

Common Networking Devices Routers are slower than bridges and switches, but make “smart” decisions on how to route (or send) packets received on one port to a network on another port. Routers contain tables of network addresses along with optimal destination routes to other networks.

Server Components Server components are those components that are used exclusively with the network server. End users depend on the server to provide the services required. To keep the server running at it is optimal performance, a higher level of preventive maintenance must be maintained.

LAN Architectures

Ethernet The Ethernet architecture is based on the IEEE standard. The IEEE standard specifies that a network implements the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access control method. Standard transfer rates are 10 Mbps or 100 Mbps, but new standards provide for gigabit Ethernet, which are capable of attaining speeds up to 1 Gbps over fiber-optic cable or other high-speed media.

Ethernet 10BASE-T uses a star topology. The 10 stands for the common transmission speed of 10 MBps, the "BASE" stands for baseband mode, and the "T" stands for twisted pair cabling.

Ethernet 100BASE-X comes in several different varieties. It can be implemented over 4-pair Category 3, 4, or 5 UTP (100BASE-T). It can also be implemented over 4-pair Category 5 UTP or Shielded Twisted Pair (STP) (100BASE-TX), or as Ethernet over 2-strand fiber- optic cable (100BASE-FX).

Ethernet 1000BASE-T is Gigabit Ethernet. This architecture supports data transfer rates of 1 Gbps.

Token Ring The Token Ring standards are defined in IEEE A Token Ring network uses a token (that is, a special signal) to control access to the cable. –A token is initially generated when the first computer on the network comes online. –When a computer wants to transmit, it waits for and then takes control of the token when it comes its way. –The token can travel in either direction around the ring, but only in one direction at a time.

Fiber Distributed Data Interface (FDDI) FDDI is a type of Token Ring network. It runs on fiber-optic cable, and thus combines high- speed performance with the advantages of the token- passing ring topology. It runs at 100 Mbps, and its topology is a dual ring. The outer ring is called the primary ring and the inner ring is called the secondary ring.

Networking Protocols and the OSI Model

OSI Model Overview The Open Systems Interconnection (OSI) reference model is an industry standard framework that is used to divide the functions of networking into seven distinct layers. Each layer provides specific services to the layers above and below it in order for the network to work effectively.

OSI Model Overview A message begins at the top application layer and moves down the OSI layers to the bottom physical layer. As the message descends, each successive OSI model layer adds a header to it. A header is layer-specific information that basically explains what functions the layer carried out. Conversely, at the receiving end, headers are striped from the message as it travels up the corresponding layers.

What is a Protocol? Protocol is a controlled sequence of messages that is exchanged between two or more systems to accomplish a given task. Protocol specifications define this sequence together with the format or layout of the messages that are exchanged.

Transmission Control Protocol/Internet Protocol The Transmission Control Protocol/Internet Protocol (TCP/IP) suite of protocols has become the dominant standard for inter- networking. TCP/IP represents a set of public standards that specify how packets of information are exchanged between computers over one or more networks.

Transmission Control Protocol/Internet Protocol

Internetwork Packet Exchange/Sequenced Packet Exchange Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX) is the protocol suite employed originally by Novell®. It delivers functions similar to those included in TCP/IP.

NetBEUI NetBIOS Extended User Interface (NetBEUI) is a protocol used primarily on small Windows NT networks. NetBEUI is a simple protocol that lacks many of the features that enable protocol suites such as TCP/IP to be used on networks of almost any size.

AppleTalk AppleTalk is comprised of a e set of protocols that span the seven layers of the OSI reference model. AppleTalk protocols were designed to run over the major LAN types, notably Ethernet and Token Ring, and also Apple's own LAN physical topology, LocalTalk.

TCP/IP Utilities

Overview TCP/IP is a complex collection of protocols. Most vendors implement the suite to include a variety of utilities for viewing configuration information and troubleshooting problems.

Ping Ping works by sending an ICMP echo request to the destination computer. The receiving computer then sends back an ICMP echo reply message It is also possible to use Ping to find the IP address of a host when the name is known.

ARP, RARP, NSLOOKUP Address Resolution Protocol (ARP) is the means by which networked computers map Internet Protocol (IP) addresses to physical hardware (MAC) addresses that are recognized in a local network. Machines that do not know their IP addresses use Reverse Address Resolution Protocol (RARP). It is used to obtain IP address information based on the physical or MAC address.

ARP, RARP, NSLOOKUP Nslookup returns the IP address for a given hostname. It will also do the reverse and find the host name for a specified IP address.

Netstat/tpcon The netstat command is used in Windows and UNIX/Linux to display TCP/IP connection and protocol information. The netstat command provides a list of connections that are currently active. Netstat statistics can be useful in troubleshooting TCP/IP connectivity problems.

Nbtstat The Microsoft TCP/IP stacks included in Windows operating systems provide the nbtstat utility, which is used to display NetBIOS information.

Ipconfig, winipcfg, config, and ifconfig TCP/IP configuration information can be displayed using different utilities Ipconfig – Windows NT and Windows 2000 (command-line) Winipcfg –- Windows 95, 98, and ME (graphical interface) Ifconfig – UNIX and Linux (command-line

Tracert, iptrace, and traceroute It is often useful to trace the route a packet takes on its journey from source computer to destination host. TCP/IP stacks include a route tracing utility that enables users to identify the routers through which the message passes. The options depend on the operating system: –Tracert –Iptrace –Traceroute

Connecting to the Internet

Synchronous and Asynchronous Serial lines Synchronous serial transmission – Data bits are sent together with a synchronizing clock pulse. Built- in timing mechanism coordinates the clocks of the sending and receiving devices. Asynchronous serial transmission – Data bits are sent without a synchronizing clock pulse. Uses a start bit at the beginning of each message. When the receiving device gets the start bit, it can synchronize its internal clock with the sender clock.

Modems The modem is an electronic device that is used for computer communications through telephone lines. It allows data transfer between one computer and another. There are four main types of modems: –Expansion cards –PCMCIA –External modems –Built-in modems

Dial-Up Networking, Modem Standards, AT Commands When computers use the public telephone system or network to communicate, it is called Dial-Up Networking (DUN). All modems require software to control the communication session. The set of commands that most modem software uses are known as the Hayes- compatible command set. The Hayes command set is based on a group of instructions that always begins with a set of attention characters (AT).

ISPs and Internet Backbone Providers Services of an Internet Service Provider (ISP) are required to surf the Internet. An ISP is a company that connects computers to the Internet and World Wide Web. The actual connection to the Internet is tiered. The ISP may link to a larger regional ISP, which in turn might connect to one of a number of nationwide computer centers.

ISPs and Internet Backbone Providers The current U.S. Internet infrastructure consists of a commercial backbone and a high-speed service known as the Very High-Speed Backbone Network Service (vBNS). The vBNS connects five supercomputer networks across the country: –UUNET - a division of WorldCom –Cable & Wireless USA –Sprint –AT&T –BBN Planet

ISPs and Internet Backbone Providers The ISP that cannot connect directly to the national backbone is charged a fee to connect to a regional provider that links to the national backbone through a Network Access Point (NAP). Not all the Internet traffic goes through NAPs. Some ISPs that are in the same geographic area make their own interconnections and peering agreements.

Digital Subscriber Line (DSL) Digital Subscriber Line (DSL) is an always-on technology. This means there is no need to dial up each time to connect to the Internet. DSL comes in several varieties: –Asymmetric DSL (ADSL) –High Data Rate DSL (HDSL) –Symmetric DSL (SDSL) –Very High Data Rate DSL (VDSL)

Cable Modems A cable modem acts like a LAN interface by connecting a computer to the Internet. The cable modem connects a computer to the cable company network through the same coaxial cabling that feeds cable TV (CATV) signals to a television set.

Cable Modem versus DSL Internet Technologies When it comes to comparing cable modem and DSL Internet technologies, both have their pros and cons.

ISDN Another alternative to using analog telephones lines to establish a connection is ISDN. Speed is one advantage ISDN has over telephone line connections. ISDN uses a pair of 64Kbps digital lines to connect, which provides a total of 128Kbps throughput. A telephone line connects at a maximum speed of 56Kbps, and in some areas, doesn’t even reach that.

Satellite Satellite is an option for users in rural areas or with no other access to high speed Internet service. Satellite Internet does not require a phone line or cable. Two ‑ way communication, for upload and download, is achieved with the use of a satellite dish. Download speed is up to 500 kbps while the upload speed is one ‑ tenth of that of that.