Linux+ Guide to Linux Certification Chapter Fifteen Linux Networking.

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ObjectivesDescribe the purpose and types of networks, protocols, and media access methodsUnderstand basic configuration of TCP/IP protocolConfigure a NIC interface to use TCP/IP protocolConfigure a modem, ISDN, and DSL interface to use the PPP and TCP/IP protocolsUnderstand the purpose of hostnames and how they are resolved to IP addressesUse common network utilities to interact with network servicesIdentify and configure common network servicesNetworks and TCP/IPTwo or more computers connected with media that can exchange information are called a networkNetworks that connect computers within close proximity are called Local Area Networks (LANs)Networks that connect computers separated by large distances are Wide Area Networks (WANs)Special computers called routers transfer information from one network to anotherNetworks and TCP/IPProtocolsSet of rules of communication used between computers on a networkPacketsPackages of data formatted by a network protocolMedia access methodA system that defines how computers on a network share access to the physical mediumNetworks and TCP/IPLAN protocols you may configure in Linux include:TCP/IP (Transfer Control Protocol/Internet Protocol)UDP/IP (User Datagram Protocol/Internet Protocol)IPX/SPX (Internetwork Packet Exchange/Sequence Packet Exchange)AppletalkDLC (Data Link Control)DECnet (Digital Equipment Corporation network)Networks and TCP/IPEthernetThe most common media access method used in networks todayToken RingPopular media access methodThe media access method is usually contained within the hardware on the NIC or modemThe TCP/IP ProtocolInternet Protocol (IP) addressSeries of four 8-bit numbers that represent a computer on a networkUsed by a computer on the network to identify itself to other computersSubnet maskSeries of four 8-bit numbers that determine the network and host portions of an IP addressDefault gatewayIP address on router that sends packets to remote networksThe TCP/IP ProtocolFigure 15-1: A sample IP address and subnet maskConfiguring a NIC Interfaceifconfig commandCan be used to assign a TCP/IP configuration to a NIC as well as view the configuration of all network interfaces in the computerpacket internet groper (ping) commandUsed to check the connectivity on a networkConfiguring a NIC InterfaceFigure 15-2: Configuring network hardwareConfiguring a NIC InterfaceFigure 15-3: Configuring a network deviceConfiguring a NIC InterfaceFigure 15-4: Network device propertiesConfiguring a NIC InterfaceFigure 15-5: Configuring a network protocolConfiguring a NIC InterfaceFigure 15-6: Network protocol propertiesConfiguring a NIC InterfaceLinuxconfCommon graphical configuration program that can configure network interfacesnetconfigGraphical utility used to configure the network card settings of a computerConfiguring a NIC InterfaceFigure 15-7: The Linuxconf utilityConfiguring a NIC InterfaceFigure 15-8: The netconfig utilityConfiguring a PPP InterfaceThere are three common technologies that use Point-to-Point Protocol (PPP) today to connect computers to a network such as the Internet:ModemsISDNDSLConfiguring a PPP InterfaceFigure 15-9: Configuring a new PPP deviceConfiguring a PPP InterfaceFigure 15-10: Configuring a modem deviceConfiguring a PPP InterfaceFigure 15-11: Configuring user account informationConfiguring a PPP InterfaceFigure 15-12: Configuring ISDN hardwareConfiguring a PPP InterfaceFigure 15-13: Configuring user account information Configuring a PPP InterfaceFigure 15-14: Configuring a DSL connectionConfiguring a PPP InterfaceFigure 15-15: Activating a PPP connectionConfiguring a PPP InterfaceFigure 15-16: The kppp utilityName ResolutionHostnamesUser-friendly name assigned to a computerFully Qualified Domain Name (FQDN)Hostname that follows DNS conventionDomain Name Space (DNS)Network device used t resolve FQDNs to the appropriate IP addressName ResolutionFigure 15-17: The Domain Name SpaceDownloading Files Using FTPFigure 15-18: Using a Web browser FTP clientDownloading Files Using FTPTable 15-1: Common FTP commandsDownloading Files Using FTPTable 15-1 (continued): Common FTP commandsAccessing Files with NFSNetwork File System (NFS) is another common method for transferring files amongst UNIX and Linux computersNot as common as FTPTo access files using NFS, you simply mount a directory from a remote computer on the network that has the NFS daemons started to a local directoryAccessing Windows Filessmbmount commandUsed to mount directories from Windows computers to mount points from the Internet Super Daemonsmbclient utilityUsed to connect to shared resources on a Windows systemRunning Remote ApplicationsOn large Linux systems, users typically gain access to a BASH shell by using the utility that connects to the server across the networkThe most common utility used to obtain a BASH shell from a remote Linux utility computer on the network is telnetTrusted accessConfiguration where computers are allowed to access a given computer without having to provide a password firstAccessing E-mailFigure 15-19: Configuring a new e-mail accountAccessing E-mailFigure 15-20: Specifying user informationAccessing E-mailFigure 15-21: Configuring a POP, IMAP, and SMTP serverAccessing E-mailFigure 15-22: Specifying a user nameAccessing E-mailFigure 15-23: Specifying an account nameAccessing E-mailFigure 15-24: The Mozilla e-mail clientCommon Network ServicesPortNumber that uniquely identifies a network serviceWell-known portOf the 65535 possible ports, the ones from 0 to 1024 used by common networking servicesInternet Super Daemon (xinetd)Responsible for initializing and configuring many networking services on a Linux computerCommon Network ServicesFigure 15-25: Interacting with network servicesCommon Network ServicesStandalone daemonsDaemons normally started at boot-up that configure themselves without assistance from the Internet Super DaemonThe ntsysv utility can be used to configure most standalone daemons to start in various runlevelCommon Network ServicesTable 15-2: Common network servicesCommon Network ServicesTable 15-2 (continued): Common network servicesCommon Network ServicesTable 15-2 (continued): Common network servicesCommon Network ServicesAnother example of a network service that is provided directly by the Linux kernel is routingRoute tableTable of information used to indicate which networks are connected to network interfacesCommon Network ServicesMultihomed hostsComputer that has more than one network interfaceIP forwardingAct of forwarding TCP/IP packets from one network to anotherRoutingAct of forwarding data packets from one network to anotherCommon Network Servicestraceroute commandCommon utility used to troubleshoot routingDisplays all routers between the current computer and a remote computerSome network services involve a large number of daemons and require a great deal of configurationChapter SummaryA network is a collection of computers that are connected together and share informationProtocols define the format of information that is transmitted across a networkEach computer on a TCP/IP network must have a valid IP address and subnet maskThe /etc/sysconfig/network-scripts directory contains the configuration for NIC and PPP interfacesChapter SummaryThe TCP/IP configuration of a network interface may be specified manually, or obtained automatically from a DHCP or BOOTP serverHostnames are used to identify computers on a network easilyHostnames must be resolved to an IP address before network communication can take placeFiles, applications, and e-mail may be accessed across the network with the appropriate network utilityChapter SummaryNetwork services are typically provided by daemons that listen to network portsSome network services, such as firewall and routing services, are provided by the Linux kernelNIS can be used to share key configuration files across Linux computers that participate in an NIS domain


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