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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 E
-
mail

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

Accessing E
-
mail

Figure 15
-
20:
Specifying
user
information

Accessing E
-
mail

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

Accessing E
-
mail

Figure 15
-
22:
Specifying a
user name

Accessing E
-
mail

Figure 15
-
23:
Specifying an
account name

Accessing E
-
mail

Figure 15
-
24:
The Mozilla
e
-
mail client

Common 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 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 e
-
mail 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