Linux+ Guide to Linux Certification

Chapter Fifteen

Linux Networking

ObjectivesObjectives

• Describe the purpose and types of networks, protocols, and media access methods

• Understand basic configuration of TCP/IP protocol• Configure a NIC interface to use TCP/IP protocol• Configure a modem, ISDN, and DSL interface to use the PPP

and TCP/IP protocols• Understand the purpose of hostnames and how they are

resolved to IP addresses• Use common network utilities to interact with network

services• Identify and configure common network services

Networks and TCP/IPNetworks and TCP/IP

• Two or more computers connected with media that can exchange information are called a network

• Networks 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 another

Networks and TCP/IPNetworks and TCP/IP

• Protocols– Set of rules of communication used between

computers on a network

• Packets– Packages of data formatted by a network protocol

• Media access method– A system that defines how computers on a

network share access to the physical medium

Networks and TCP/IPNetworks and TCP/IP

• LAN 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)

– Appletalk

– DLC (Data Link Control)

– DECnet (Digital Equipment Corporation network)

Networks and TCP/IPNetworks and TCP/IP

• Ethernet– The most common media access method used in

networks today

• Token Ring– Popular media access method

• The media access method is usually contained within the hardware on the NIC or modem

The TCP/IP ProtocolThe TCP/IP Protocol

• Internet Protocol (IP) address– Series of four 8-bit numbers that represent a computer on

a network– Used by a computer on the network to identify itself to

other computers

• Subnet mask– Series of four 8-bit numbers that determine the network

and host portions of an IP address

• Default gateway– IP address on router that sends packets to remote

networks

The TCP/IP ProtocolThe TCP/IP Protocol

Figure 15-1: A sample IP address and subnet mask

Configuring a NIC InterfaceConfiguring a NIC Interface

• ifconfig command– Can be used to assign a TCP/IP configuration to a

NIC as well as view the configuration of all network interfaces in the computer

• packet internet groper (ping) command– Used to check the connectivity on a network

Configuring a NIC InterfaceConfiguring a NIC Interface

Figure 15-2: Configuring network hardware

Configuring a NIC InterfaceConfiguring a NIC Interface

Figure 15-3: Configuring a network device

Configuring a NIC InterfaceConfiguring a NIC Interface

Figure 15-4: Network device properties

Configuring a NIC InterfaceConfiguring a NIC Interface

Figure 15-5: Configuring a network protocol

Configuring a NIC InterfaceConfiguring a NIC Interface

Figure 15-6: Network protocol properties

Configuring a NIC InterfaceConfiguring a NIC Interface

• Linuxconf– Common graphical configuration program that

can configure network interfaces

• netconfig– Graphical utility used to configure the network

card settings of a computer

Configuring a NIC InterfaceConfiguring a NIC Interface

Figure 15-7: The Linuxconf utility

Configuring a NIC InterfaceConfiguring a NIC Interface

Figure 15-8: The netconfig utility

Configuring a PPP InterfaceConfiguring a PPP Interface

• There are three common technologies that use Point-to-Point Protocol (PPP) today to connect computers to a network such as the Internet:– Modems– ISDN– DSL

Configuring a PPP InterfaceConfiguring a PPP Interface

Figure 15-9: Configuring a new PPP device

Configuring a PPP InterfaceConfiguring a PPP Interface

Figure 15-10: Configuring a modem device

Configuring a PPP InterfaceConfiguring a PPP Interface

Figure 15-11: Configuring user account information

Configuring a PPP InterfaceConfiguring a PPP Interface

Figure 15-12: Configuring ISDN hardware

Configuring a PPP InterfaceConfiguring a PPP Interface

Figure 15-13: Configuring user account information

Configuring a PPP InterfaceConfiguring a PPP Interface

Figure 15-14: Configuring a DSL connection

Configuring a PPP InterfaceConfiguring a PPP Interface

Figure 15-15: Activating a PPP connection

Configuring a PPP InterfaceConfiguring a PPP Interface

Figure 15-16: The kppp utility

Name ResolutionName Resolution

• Hostnames– User-friendly name assigned to a computer

• Fully Qualified Domain Name (FQDN)– Hostname that follows DNS convention

• Domain Name Space (DNS)– Network device used t resolve FQDNs to the

appropriate IP address

Name ResolutionName Resolution

Figure 15-17: The Domain Name Space

Downloading Files Using FTPDownloading Files Using FTP

Figure 15-18: Using a Web browser FTP client

Downloading Files Using FTPDownloading Files Using FTP

Table 15-1: Common FTP commands

Downloading Files Using FTPDownloading Files Using FTP

Table 15-1 (continued): Common FTP commands

Accessing Files with NFSAccessing Files with NFS

• Network File System (NFS) is another common method for transferring files amongst UNIX and Linux computers– Not as common as FTP– To 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 directory

Accessing Windows FilesAccessing Windows Files

• smbmount command– Used to mount directories from Windows

computers to mount points from the Internet Super Daemon

• smbclient utility– Used to connect to shared resources on a

Windows system

Running Remote ApplicationsRunning Remote Applications

• On large Linux systems, users typically gain access to a BASH shell by using the utility that connects to the server across the network– The most common utility used to obtain a BASH

shell from a remote Linux utility computer on the network is telnet

• Trusted access– Configuration where computers are allowed to access

a given computer without having to provide a password first

Accessing E-mailAccessing E-mail

Figure 15-19: Configuring a new e-mail account

Accessing E-mailAccessing E-mail

Figure 15-20: Specifying user information

Accessing E-mailAccessing E-mail

Figure 15-21: Configuring a POP, IMAP, and SMTP server

Accessing E-mailAccessing E-mail

Figure 15-22: Specifying a user name

Accessing E-mailAccessing E-mail

Figure 15-23: Specifying an account name

Accessing E-mailAccessing E-mail

Figure 15-24: The Mozilla e-mail client

Common Network ServicesCommon Network Services

• Port– Number that uniquely identifies a network service

• Well-known port– Of the 65535 possible ports, the ones from 0 to

1024 used by common networking services

• Internet Super Daemon (xinetd)– Responsible for initializing and configuring many

networking services on a Linux computer

Common Network ServicesCommon Network Services

Figure 15-25: Interacting with network services

Common Network ServicesCommon Network Services

• Standalone daemons– Daemons normally started at boot-up that

configure themselves without assistance from the Internet Super Daemon

– The ntsysv utility can be used to configure most standalone daemons to start in various runlevel

Common Network ServicesCommon Network Services

Table 15-2: Common network services

Common Network ServicesCommon Network Services

Table 15-2 (continued): Common network services

Common Network ServicesCommon Network Services

Table 15-2 (continued): Common network services

Common Network ServicesCommon Network Services

• Another example of a network service that is provided directly by the Linux kernel is routing

• Route table– Table of information used to indicate which

networks are connected to network interfaces

Common Network ServicesCommon Network Services

• Multihomed hosts– Computer that has more than one network

interface

• IP forwarding– Act of forwarding TCP/IP packets from one

network to another

• Routing– Act of forwarding data packets from one network

to another

Common Network ServicesCommon Network Services

• traceroute command– Common utility used to troubleshoot routing– Displays all routers between the current computer

and a remote computer

• Some network services involve a large number of daemons and require a great deal of configuration

Chapter SummaryChapter Summary

• A network is a collection of computers that are connected together and share information

• Protocols define the format of information that is transmitted across a network

• Each computer on a TCP/IP network must have a valid IP address and subnet mask

• The /etc/sysconfig/network-scripts directory contains the configuration for NIC and PPP interfaces

Chapter SummaryChapter Summary

• The TCP/IP configuration of a network interface may be specified manually, or obtained automatically from a DHCP or BOOTP server

• Hostnames are used to identify computers on a network easily

• Hostnames must be resolved to an IP address before network communication can take place

• Files, applications, and e-mail may be accessed across the network with the appropriate network utility

Chapter SummaryChapter Summary

• Network services are typically provided by daemons that listen to network ports

• Some network services, such as firewall and routing services, are provided by the Linux kernel

• NIS can be used to share key configuration files across Linux computers that participate in an NIS domain