Linux is increasingly popular in the computer networking/telecommunications industry.
Acquiring the Linux operating system is a relatively simple and inexpensive task
since virtually all of the source code can be downloaded from several different
FTP or HTTP sites on the Internet. In addition, the most recent version of Red Hat
Linux can be purchased from computer retail stores for between $25 and $50, depending
on whether you purchase the standard or full version. The retail brand is indeed
a worthwhile investment (vs. the free FTP or HTTP versions) since valuable technical
support is included directly from the Red Hat Linux engineers for at least a year.
This can be very helpful if, for instance, you can not resolve an installation/configuration
problem after consulting the Red Hat Linux manuals.
This article describes how to put together a Local Area Network (LAN) consisting
of two or more computers using the Red Hat Linux 6.2 operating system. A LAN
is a communications network that interconnects a variety of devices and provides
a means for exchanging information among those devices. The size and scope of a
LAN is usually small, covering a single building or group of buildings. In a LAN,
modems and phone lines are not required, and the computers should be close enough
to run a network cable between them.
For each computer that will participate in the LAN, you'll need a network interface
card (NIC) to which the network cable will be attached. You will also need to assign
a unique hostname and IP address to each computer in the LAN (described later in
this article), but this requires a basic understanding of TCP/IP (Transmission Control
Protocol/Internet Protocol).
Introduction to TCP/IP
TCP/IP is the suite of protocols used by the Internet and most LANs throughout the
world. In TCP/IP, every host (computer or other communications device) that is connected
to the network has a unique IP address. An IP address is composed of four octets
(numbers in the range of 0 to 255) separated by decimal points. The IP address is
used to uniquely identify a host or computer on the LAN. For example, a computer
with the hostname Morpheus could have an IP address of 192.168.7.127. You should
avoid giving two or more computers the same IP address by using the range of IP
addresses that are reserved for private, local area networks; this range of IP addresses
usually begins with the octets 192.168.
LAN network address The first three octets of an IP address should be the
same for all computers in the LAN. For example, if a total of 128 hosts exist in
a single LAN, the IP addresses could be assigned starting with 192.168.1.x,
where x represents a number in the range of 1 to 128. You could create consecutive
LANs within the same company in a similar manner consisting of up to another 128
computers. Of course, you are not limited to 128 computers, as there are other ranges
of IP addresses that allow you to build even larger networks.
There are different classes of networks that determine the size and total possible
unique IP addresses of any given LAN. For example, a class A LAN can have over 16
million unique IP addresses. A class B LAN can have over 65,000 unique IP addresses.
The size of your LAN depends on which reserved address range you use and the subnet
mask (explained later in the article) associated with that range (see Table 1.).
Table 1. Address ranges and LAN sizes
Address range | Subnet mask | Provides | Addresses per LAN |
10.0.0.0 - 10.255.255.255.255 | 255.0.0.0 | 1 class A LAN | 16,777,216 |
172.16.0.0 - 172.31.255.255 | 255.255.0.0 | 16 class B LANs | 65,536 |
192.168.0.0 - 192.168.255.255 | 25.255.255.0 | 256 class C LANs | 256 |
Network and broadcast addresses
Another important aspect of building a LAN is that the addresses at the two extreme
ends of the address range are reserved for use as the LAN's network address and
broadcast address. The network address is used by an application to represent
the overall network. The broadcast address is used by an application to send
the same message to all other hosts in the network simultaneously.
For example, if you use addresses in the range of 192.168.1.0 to 192.168.1.128,
the first address (192.168.1.0) is reserved as the network address, and the last
address (192.168.1.128) is reserved as the broadcast address. Therefore, you only
assign individual computers on the LAN IP addresses in the range of 192.168.1.1
to 192.168.1.127:
Network address: | 192.168.1.0 |
Individual hosts: | 192.168.1.1 to 192.168.1.127 |
Broadcast address: | 192.168.1.128 |
Subnet masks
Each host in a LAN has a subnet mask. The subnet mask is an octet that uses
the number 255 to represent the network address portion of the IP address and a
zero to identify the host portion of the address. For example, the subnet mask 255.255.255.0
is used by each host to determine which LAN or class it belongs to. The zero at
the end of the subnet mask represents a unique host within that network.
Domain name
The domain name, or network name, is a unique name followed by a standard
Internet suffixes such as .com, .org, .mil, .net, etc. You can pretty much name
your LAN anything if it has a simple dial-up connection and your LAN is not a server
providing some type of service to other hosts directly. In addition, our sample
network is considered private since it uses IP addresses in the range of 192.168.1.x.
Most importantly, the domain name of choice should not be accessible from the Internet
if the above constraints are strictly enforced. Lastly, to obtain an "official"
domain name you could register through InterNIC, Network Solutions or Register.com.
See the Resources section later in this article for the
Web sites with detailed instructions for obtaining official domain names.
Hostnames
Another important step in setting up a LAN is assigning a unique hostname to each
computer in the LAN. A hostname is simply a unique name that can be made up and
is used to identify a unique computer in the LAN. Also, the name should not contain
any blank spaces or punctuation. For example, the following are valid hostnames
that could be assigned to each computer in a LAN consisting of 5 hosts: hostname
1 - Morpheus; hostname 2 - Trinity; hostname 3 - Tank; hostname 4 - Oracle; and
hostname 5 - Dozer. Each of these hostnames conforms to the requirement that no
blank spaces or punctuation marks are present. Use short hostnames to eliminate
excessive typing, and choose a name that is easy to remember.
Table 2 summarizes what we have covered so far in this article. Every host in the
LAN will have the same network address, broadcast address, subnet mask, and domain
name because those addresses identify the network in its entirety. Each computer
in the LAN will have a hostname and IP address that uniquely identifies that particular
host. The network address is 192.168.1.0, and the broadcast address is 192.168.1.128.
Therefore, each host in the LAN must have an IP address between 192.168.1.1 to 192.168.127.
Table 2. Sample IP addresses for a LAN with 127 or fewer interconnected
computers
IP address | Example | Same/unique |
Network address | 192.168.1.0 | Same for all hosts |
Domain name | www.yourcompanyname.com | Same for all hosts |
Broadcast address | 192.168.1.128 | Same for all hosts |
Subnet mask | 255.255.255.0 | Same for all hosts |
Hostname | Any valid name | Unique to each host |
Host addresses | 192.168.1.x | x must be unique to each host |
Assigning IP addresses in a LAN
There are two ways to assign IP addresses in a LAN. You can manually assign a static
IP address to each computer in the LAN, or you can use a special type of server
that automatically assigns a dynamic IP address to each computer as it logs
into the network.
Static IP addressing
Static IP addressing means manually assigning a unique IP address to each computer
in the LAN. The first three octets must be the same for each host, and the last
digit must be a unique number for each host. In addition, a unique hostname will
need to be assigned to each computer. Each host in the LAN will have the same network
address (192.168.1.0), broadcast address (192.168.1.128), subnet mask (255.255.255.0),
and domain name (yourcompanyname.com). It's a good idea to start by visiting each
computer in the LAN and jotting down the hostname and IP address for future reference.
Dynamic IP addressing
Dynamic IP addressing is accomplished via a server or host called DHCP (Dynamic
Host Configuration Program) that automatically assigns a unique IP address to each
computer as it connects to the LAN. A similar service called BootP can also automatically
assign unique IP addresses to each host in the network. The DHCP/ BootP service
is a program or device that will act as a host with a unique IP address. An example
of a DHCP device is a router that acts as an Ethernet hub (a communications device
that allows multiple host to be connected via an Ethernet jack and a specific port)
on one end and allows a connection to the Internet on the opposite end. Furthermore,
the DHCP server will also assign the network and broadcast addresses. You will not
be required to manually assign hostnames and domain names in a dynamic IP addressing
scheme.
The LAN hardware
Assigning hostname and IP addresses will be useless if there is no hardware available
to connect all the computers together. There are several different types of hardware
schemes such as Ethernet, Token Ring, FDDI, Token Bus, etc. Since Ethernet is the
most widely used hardware scheme, we will focus our attention on it. Ethernet is
available from several different computer vendors, and it is relatively inexpensive.
Ethernet is a 10-Mbps baseband LAN specification developed by Xerox, Intel, and
Digital Equipment. In order to build an Ethernet hub you need the following: an
Ethernet Network Interface Card (NIC) for each computer, an Ethernet compatible
hub with at least the same number of ports as there will be computers in the LAN,
and Ethernet cables (or 10BaseT cables) to connect each computer's NIC to the Ethernet
hub.
Also make sure that the hardware of choice is compatible with the Red Hat Linux
operating system. This hardware/software compatibility information is usually found
in the Requirements section on the back of the box of each product. Alternatively,
you could ask a computer sales person about hardware/software requirements. You
can usually save money by purchasing LAN cards as a package vs. purchasing them
individually.
When choosing an Ethernet hub ensure that it contains at least as many ports as
there are computers that will participate in the LAN. It is always best to choose
a hub with additional ports to allow for expansion.
If you plan to use all of the computers in the LAN to access the Internet via a
local Internet Service Provider (ISP), the router/Ethernet combo is an ideal choice.
The router/Ethernet unit is normally configured using any computer that is connected
to the LAN. Assuming that all computers in the LAN will be running the Red Hat Linux
operating system, a router will be required that can be configured using a Linux
configuration program such as LinuxConf.
Finally, choose network cables to allow for expansion. Typically, most Ethernet
networks use 10BaseT cables with RJ45 jacks at each end. It's always a good idea
to purchase cables that are 1 or 2 times longer than the required length in case
the structure (topology) of the LAN changes in the future.
Installing the hardware
Assuming that all LAN hardware is available, the next step is to install it. First
turn off all the computers that will participate in the LAN. Next, open the case
on each computer and install each NIC in the appropriate slot on the motherboard,
being careful to follow the manufacturer's instructions.
Find a convenient but safe location for the Ethernet hub, preferably a centralized
location in the same building or room along with the computers. Next, run the cable
from the NIC in each computer to the Ethernet hub ensuring all cables are out of
the way of users who will need physical access to each computer in the LAN. Moreover,
make sure you follow all instructions provided with the LAN hardware before starting
up any of the computers that will participate in the LAN.
If you are using a router to connect the LAN to the Internet or using a DHCP server,
you will need to do some configuration as required by the user's manual. Lastly,
assuming all computers are attached to the Ethernet hub via the NIC and a specific
port on the hub, you can now begin the software configuration process using the
Red Hat operating system.
Configuring the LAN
How you configure the computers on the LAN will depend on whether the Red Hat OS
was installed before or after the LAN hardware. If you installed the LAN hardware
before installing Red Hat you will be prompted for network configuration during
the Red Hat installation process. However, if you installed the Red Hat OS after
the LAN hardware, a program called "Kudzu" will detect the newly installed Ethernet
card and initiate the configuration process automatically. Follow these steps when
configuring each Ethernet card using the "Kudzu" program:
- During the bootup process look for a dialog box titled "Welcome to Kudzu." Press
Enter to begin the configuration process. - Next, you should see another dialog
box that displays the brand name for the installed Ethernet card. Press Enter again
to continue. - After a brief delay you should see "Would You Like to Set up Networking".
- Select the NO option using the Tab key and then press Enter. I will describe setting
up networking using a utility called LinuxConf later in this article.
At this point, the bootup process should continue normally and you will be required
to log on to the computer as the root user. You should have been given the opportunity
to create a root account during the initial installation of Red Hat.
Using LinuxConf to configure your Ethernet card
You can use an application program called LinuxConf to configure or reconfigure
the NIC of each computer in the LAN. You can launch the LinuxConf utility by typing
linuxconf at the command prompt of any terminal window in the KDE or
GNOME desktop environment. Another way to start the LinuxConf utility is to click
the Main menu button, select System, then LinuxConf. When the LinuxConf application
is displayed, follow the steps below to configure the Ethernet card:
- From the LinuxConf tree structure, select Config, Networking, Client Tasks, Basic
Host Information. - Type the fully qualified hostname that you assigned to this computer on the Host
name tab. - Next, click the Adaptor 1 tab, which displays your Ethernet card settings.
- Verify that the Enabled button is selected to ensure that the Ethernet card will
be accessible. - Choose the Manual option if you will not be using a DHCP or BootP
server on your LAN and continue to step 6. Otherwise, if you
will be using a DHCP or BootP server, choose either DHCP or BootP accordingly and
continue to step 12. - Enter this computer's
hostname followed by a period and the domain name of the LAN for the Primary name
+ domain option. - Enter the computer's hostname in addition to any aliases separated
by a blank space under the Aliases option. - Enter the IP address assigned to
this computer next to IP Address (such as 192.168.1.1). - Type in 255.255.255.0
for the Netmask. - For net device, type eth0, which represents the first Ethernet card located inside
the computer. - The driver or Kernel Module option for the Ethernet card should
automatically be filled in upon exiting LinuxConf. - Click
the Accept button to activate all changes. - Repeat steps 1-12 for each computer
in the LAN, verifying that you've entered the correct hostname and the corresponding
IP address.
Nameserver specification
Another important step in setting up LAN is to configure the Nameserver specification,
which is used by Linux to look up IP addresses when only the computer's hostname
is given. There are two methods that are used by Red Hat Linux to resolve hostnames
into IP addresses. One method is via Domain Name Services (DNS), and the other is
by means of a local file at /etc/hosts. Locate the hosts file by typing cd /etc
to change to the /etc directory. The /etc directory is where most system configuration
files are found for each computer. Next, follow the steps below to resolve hostnames
into IP address using the /etc/hosts file:
- In the left column of LinuxConf, open the Nameserver specification (DNS) category.
Left-click the DNS Usage option. (The button should be pushed in.)- Enter localdomain
next to the Search Domain 1 category. - If you know the primary and secondary
IP addresses for the nameserver, which should be available for this Ethernet card,
enter those in the IP of nameserver 1 and IP of nameserver 2 categories. Otherwise,
you can leave those categories blank. - Left-click the Accept button to activate
all changes.
Hostname search path
The hostname search path is used by Red Hat Linux to search for IP addresses assigned
to hostnames. To configure the hostname search path so that the local host (/etc/hosts)
file is used to resolve local hostnames, and the ISP domain services to resolve
Internet domain services, follow these steps:
- In the left column of LinuxConf, open the Routing and Gateways category.
Select the Host Name Search path option.- In the right column of LinuxConf, select
the Multiple IPs for One Host option. - Select the hosts, dns option in the right
portion of LinuxConf. - Left-click the Accept button to activate all changes.
Setting up /etc/hosts
The Red Hat Linux OS needs some way to find IP addresses within the LAN based on
the each computer's hostname. I described earlier in the article that the Domain
Name Service (DNS) is one method of resolving hostnames into IP addresses. In a
DNS configuration the hostnames and IP addresses should already be listed in a pre-existing
nameserver. Consult your local ISP to obtain those IP addresses. On the other hand,
if there is a centralized nameserver, as with small LANs, a host file will need
to be configured on each computer that was assigned a hostname, IP address, and
any aliases. This configuration process involves editing a text file located at
/etc/host. You will need to go to one of the computers in the LAN and follow the
below steps in order to create and configure the /etc/hosts file:
- In the left column of LinuxConf, open the Misc category.
- Open the Information
about hosts category. You should see an entry for this computer that includes the
IP address, hostname, and any aliases. - Left-click the Add button once to add
an entry for another host in the LAN. - Type the Primary + Domain Name for another
host in the LAN in the dialog box that appears (such as trinity.yourcompanyname.com).
Type one or more aliases for this computer next to the Alias option (such as tank).
Enter the IP address for the hostname that you've assigned for this computer next
to IP number.- Left-click the Accept button to activate all changes.
Repeat steps 1-7 for each computer in your LAN.
After you have done steps 1-7 for all computers, the /etc/hosts tab of LinuxConf
should list one entry for every computer in your LAN, in addition to the local host's
loopback interface. The local host name should appear as localhost. Finally, you
can save all changes and exit the LinuxConf application by following the steps below:
- Left-click the Quit button in the /etc/host screen after all hostnames and IP addresses
have been entered. - To exit the LinuxConf application, left-click the Quit button
at the bottom-left corner. - Left-click the Activate the Changes button to activate
all changes and exit LinuxConf.
Repeat for every host
Now that you have configured one computer in you LAN, you will need to go back and
repeat all the above steps for each computer starting with the section
"Configuring the LAN". If you would prefer a less time-consuming procedure
of configuring each computer, you can modify the /etc/hosts file on each computer
manually using a copy method.
You can copy the /etc/hosts file that you have just created to a floppy disk or
CD-ROM (if you have a writeable CD-ROM drive) and copy that file to the /etc directory
of each computer in your LAN. To copy the /etc/hosts file to a floppy disk, type
the command cp /etc/hosts /mnt/floppy at the command prompt. Do this
on the computer where you configured the initial /etc/hosts file using the LinuxConf
utility.
Next, take the floppy to each computer in the LAN and type the command cp /mnt/floppy in a terminal window. This will copy the hosts file to
hosts /etc/host
the /etc directory on each host. If you are using a CD-ROM, replace the /mnt/floppy/
in the above commands with //mnt/cdrom/ to copy files to and from a
writeable CD-ROM. The /etc/hosts file, as you probably noticed, is just a text file
with a list of hostnames and IP addresses separated into three columns. Lastly,
make sure that the local computer and its associated IP address are listed twice
and all the other computers in the LAN are listed only once.
Testing the LAN
To test the completely configured LAN, make sure that the computers are able to
communicate with each other after the bootup process. You can start by typing
reboot
This allows you to monitor the testing information that scrolls down the screen
as a standard procedure during the Linux boot process. Look for the following information:
Setting hostname: | <hostname you assigned to this computer> |
Bringing up Interface lo: | <OK> or <FAILED> |
Bringing up interface eth0 | <OK> or <FAILED> |
The Setting hostname field should display the hostname that you assigned for this
computer. The lo and eth0 interfaces should display [OK] to indicate that both tests
were successful.
To determine whether each computer can communicate with every other computer in
the LAN, use the ping command. Open any terminal window on the current host and
type the command ping <IP address> or <hostname>, where
<IP address> or <hostname> is the IP address and/or the hostname that
you assigned to this computer. Note that you must type either the IP address or
the hostname in order for the ping command to work properly.
If you have configured the DNS nameserver specification properly, the ping <hostname>
command should resolve the hostname into a corresponding IP address. Otherwise,
you will need to use the IP address that you should currently already have listed
for all computers in the LAN. The ping command will send messages across the LAN
to the designated IP address or computer. You should see several messages or packets
(consisting of bytes of information) if the computers are "talking" or communicating
with each other. These packets look similar to the following:
64 bytes from 192.168.1.x : icmp_seq=0 ttl=255 time=0.8ms |
Note that the "192.168.1" represents the LAN that this particular host is a member
of and the x indicates the specific host number that you are attempting to ping
(e.g. such as Oracle) which jointly makes up the IP address. You can press the Ctrl+C
to terminate the test and you should see the following basic information about the
entire ping test:
--- hostname.yourcompanyname.com ping statistics --- |
Verify that the packet loss is 0%, which is an immediate indication that the test
was successful. However, there is a problem if the ping command results in the following
message:
From hostname.comanyname.com (192.168.1.1): Destination Host Unreachable |
This is an immediate indication that the two computers are not communicating at
all. If the computers are not communicating, see the next section, "Troubleshooting
the LAN". Otherwise, when you can successfully ping all other computers
in the LAN from one designated computer, the overall basic communications functionality
is indeed a success. At this point, you can consider this LAN to be a fully functional
network that you can install and on which you can configure various network services
as desired.
Troubleshooting the LAN
If you are unable to ping another computer in the LAN, here's how to get to the
source of the problem. First of all, it's a good idea to shut down every computer
in the LAN using the halt command. At the command prompt on each computer, type
halt. The main reason for shutting down all computers is to monitor
feedback from the boot process when each computer is started up again.
Check all cable connections between every computer, making sure that all RJ45 jacks
are connected properly. After verifying that all the cables are secured properly,
start each computer one at a time and look for the following response during the
boot process:
Setting hostname: hostname.networkname [OK] |
You can turn on the interactive mode by typing I at the LILO boot prompt during
the initial bootup process of Red Hat to get a closer view of the feedback. Ensure
that the hostname and network name that was assigned to this computer is spelled
correctly. If this is not the case, you will need to return to the Basic Host Information
section of LinuxConf. In interactive mode you will be prompted to start several
services. Respond to each question with Yes and pay close attention to results of
various tests. If the Kudzu program detects an Ethernet card, then this an indication
that the card was not properly configured the first time around. Proceed to let
Kudzu configure the card. When you are prompted to configure the network, choose
"Yes" and type the correct IP address and other related information for this particular
computer.
Another important response to examine carefully is the following:
Bringing up interface eth0 [OK] |
This line indicates whether the Ethernet card is working properly. If this test
fails you should check all network settings using LinuxConf to ensure that the card
was configured properly. If the network settings are correct, there is probably
a defect in the Ethernet card itself. In order to verify this, consult the manufacturer
of the Ethernet card or a computer technician to determine whether or not the card
is defective. Repeat the preceding troubleshooting procedures on each new Ethernet
card installed.
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