Linux+ Guide to Linux Certification Chapter Fifteen Linux Networking

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

Configuring 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 Interface Figure 15-2: Configuring network hardware

Configuring a NIC Interface Figure 15-3: Configuring a network device

Configuring a NIC Interface Figure 15-4: Network device properties

Configuring a NIC Interface Figure 15-5: Configuring a network protocol

Configuring a NIC Interface Figure 15-6: Network protocol properties

Configuring 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 Interface Figure 15-7: The Linuxconf utility

Configuring a NIC Interface Figure 15-8: The netconfig utility

Configuring 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 Interface Figure 15-9: Configuring a new PPP device

Configuring a PPP Interface Figure 15-10: Configuring a modem device

Configuring a PPP Interface Figure 15-11: Configuring user account information

Configuring a PPP Interface Figure 15-12: Configuring ISDN hardware

Configuring a PPP Interface Figure 15-13: Configuring user account information

Configuring a PPP Interface Figure 15-14: Configuring a DSL connection

Configuring a PPP Interface Figure 15-15: Activating a PPP connection

Configuring a PPP Interface Figure 15-16: The kppp utility

Name 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 Resolution Figure 15-17: The Domain Name Space

Downloading Files Using FTP Figure 15-18: Using a Web browser FTP client

Downloading Files Using FTP Table 15-1: Common FTP commands

Downloading Files Using FTP Table 15-1 (continued): Common FTP commands

Accessing 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 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 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 Figure 15-19: Configuring a new account

Accessing Figure 15-20: Specifying user information

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

Accessing Figure 15-22: Specifying a user name

Accessing Figure 15-23: Specifying an account name

Accessing Figure 15-24: The Mozilla client

Common Network Services Port –Number that uniquely identifies a network service Well-known port –Of the 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 Services Figure 15-25: Interacting with network services

Common 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 Services Table 15-2: Common network services

Common Network Services Table 15-2 (continued): Common network services

Common Network Services Table 15-2 (continued): Common network services

Common 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 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 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 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 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 may be accessed across the network with the appropriate network utility

Chapter 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