lsg28.htm

linux-unix130.linux.and.unix.ebooks130 linux and unix ebookslinuxLearning Linux - Collection of 12 E

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<FONT SIZE=4 COLOR="#FF0000"><B>Network Operating System</B></FONT></CENTER></H4>



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<P>A network operating system&#151;often called a NOS&#151;controls the interactions between all the machines on the network. The NOS is responsible for controlling the way information is sent over the network medium (a coaxial or twisted pair cable, for example). It handles the way in which data from a machine is packaged and sent to others, as well as what happens when two or more machines try to send information at the same time. The NOS can also handle shared peripherals, such as a laser printer, scanner, or CD-ROM drive that is on one machine but is accessible by other machines on the network.



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<P>With local area networks that have a single server and many clients hanging off it, the NOS resides on the server. This is the way Novell's NetWare works. The main part of the NOS sits on the server, while smaller client software packages are loaded onto each client.



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<P>With larger networks that don't use a single server, such as a Linux network running TCP/IP, the NOS may be part of each machine's software. Linux, for example, has the networking code for TCP/IP built into the operating system kernel so it is always available. A PC that wants to connect to the TCP/IP network must have a software package installed that handles the TCP/IP protocol.



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<P>Networks such as Microsoft Windows for Workgroups and Artisoft's LANtastic do not use a single primary server (although they can). Instead, each machine acts as its own server, containing all the NOS that is needed to talk to any other machine on the network.



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<FONT SIZE=4 COLOR="#FF0000"><B>Network Protocols</B></FONT></CENTER></H4>



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<P>The network protocol is the name of the communications system by which machines on the network interact. On a UNIX system, for example, TCP/IP (Transmission Control Protocol/Internet Protocol) is the most common. TCP/IP is the network protocol. (Actually, TCP/IP is a whole family of protocols, but we'll deal with that later.) Novell NetWare usually uses a network protocol called IPX (InterPacket Exchange).



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<P>The different protocols mostly use the same approach to communications: they assemble information into blocks of data called a packet, and send that across the network. However, the way the packet is made up, and the type of information attached to control its routing, differs with each NOS.



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<FONT SIZE=4 COLOR="#FF0000"><B>Network Interface Card</B></FONT></CENTER></H4>



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<P>The network interface card (NIC) is an adapter that usually sits in a slot inside your PC. Some NICs now plug into parallel or SCSI ports on the back of your system. These are very useful for portable machines, although they are still rare for desktops.



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<P>The network interface card handles the connection to the network itself through one or more connectors on the backplane of the card. The most common network connectors are similar to telephone jacks, with coaxial cable (like cable TV) a close second. You must make sure that the network interface card you are using in your machine works with the network operating system.



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<FONT SIZE=4 COLOR="#FF0000"><B>Bridges, Routers, and Brouters</B></FONT></CENTER></H4>



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<P>You may hear the terms bridge and router often. They are simply machines that connect two or more networks together. The difference between a bridge and a router is that a bridge simply connects two local area networks running the same network operating system (it acts as a bridge between two LANs primarily to reduce traffic on the larger network), while a router connects LANs that may be running different operating systems. The router can have special software that converts one NOS' packets to the other's.



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<P>A router is more complicated than a bridge, in that it can make decisions about where and how to send packets of information (routing it, hence the name) to its destination. A brouter is a relatively new device that combines the capabilities of both bridges and routers (hence its name).



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<FONT SIZE=4 COLOR="#FF0000"><B>Gateways</B></FONT></CENTER></H4>



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<P>In common usage terms, a gateway is a machine that acts as an interface between a small network and a much larger one, such as a local area network connecting to the Internet. Gateways are also used in large corporations, for example, to connect small, office-based LANs to the larger corporate mainframe network. Usually, the gateway connects to a high-speed network cable or medium called the backbone. More formally, a gateway can perform protocol translations between two networks.



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<FONT SIZE=5 COLOR="#FF0000"><B>What Is TCP/IP?</B></FONT></CENTER></H3>



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<P>Put in simple terms, TCP/IP is the name of a networking protocol family. Protocols are sets of rules that all companies and software products must adhere to in order to make their products compatible with each other. A protocol defines how software will communicate with each other. A protocol also defines how each part of the overall package manages the transfer of information.



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<P>In essence, a protocol is a written set of guidelines that defines how two applications or machines can communicate with each other, each conforming to the same standards. TCP/IP is not restricted to the Internet. It is the most widely used networking software protocol in the world, used for large, multi-site, corporate local area networks as well as small, three- or four-PC LANs.



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<P>TCP/IP stands for Transmission Control Protocol/Internet Protocol, which are really two separate protocols. Despite what many people think, the term TCP/IP refers to a whole family of related protocols, all designed to transfer information across a network. TCP/IP is designed to be the software component of a network. The parts of the TCP/IP protocol family all have dedicated tasks, such as sending electronic mail, transferring files, providing remote logon services, routing messages, or handling network crashes.



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<P>The different services involved with TCP/IP and their functions can be grouped according to purpose. Transport protocols control the movement of data between two machines and include the following:



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<LI><B>TCP (Transmission Control Protocol)</B>  A connection-based service, meaning that the sending and receiving machines are connected and communicating with each other at all times.



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<LI><B>UDP (User Datagram Protocol)</B>  A connectionless service, meaning that the data is sent without the sending and receiving machines being in contact with each other. It's like sending snail-mail (regular postal service) with an address but with no way of knowing whether the mail will ever be delivered.



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<P>Routing protocols handle the addressing of the data and determine the best means of getting to the destination. They can also handle the way large messages are broken up and reassembled at the destination:



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<LI><B>IP (Internet Protocol)</B>  Handles the actual transmission of data.



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<LI><B>ICMP (Internet Control Message Protocol)</B>  Handles status messages for IP, such as error and changes in network hardware that affect routing.



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<LI><B>RIP (Routing Information Protocol)</B>  One of several protocols that determine the best routing method to deliver a message.



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<LI><B>OSPF (Open Shortest Path First)</B>  An alternate protocol for determining routing.



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<P>Network Address protocols handle the way machines are addressed, both by a unique number and a name:



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<LI><B>ARP (Address Resolution Protocol)</B>  Determines the unique numeric addresses of machines on the network.



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<LI><B>DNS (Domain Name System)</B>  Determines numeric addresses from machine names.



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<LI><B>RARP (Reverse Address Resolution Protocol)</B>  Determines addresses of machines on the network, but in a backwards manner from ARP.



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<P>User Services are applications a user (or a machine) can use:



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<LI><B>BOOTP (Boot Protocol)</B>  Starts up a network machine by reading the boot information from a server.



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<LI><B>FTP (File Transfer Protocol)</B>  Transfers files from one machine to another.



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<LI><B>TELNET</B>  Allows remote logins, which means a user on one machine can connect to another and behave as through he or she were sitting at the remote machine's keyboard.



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<P>Gateway Protocols help the network communicate routing and status information, as well as handle data for local networks:



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<LI><B>EGP (Exterior Gateway Protocol)</B>  Transfers routing information for external networks.



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<LI><B>GGP (Gateway-to-Gateway Protocol)</B>  Transfers routing information between gateways.



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<LI><B>IGP (Interior Gateway Protocol)</B>  Transfers routing information for internal networks.



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