Thursday, August 5, 2010

Linux Ubuntu Server 10.04 Chapter 3 Networking


Ubuntu ships with a number of graphical utilities to configure your network devices. This document is geared toward server administrators and will focus on managing your network on the command line.

Ethernet interfaces are identified by the system using the naming convention of ethX, where X
represents a numeric value. The first Ethernet interface is typically identified as eth0, the second as eth1, and all others should move up in numerical order.

To quickly identify all available Ethernet interfaces, you can use the ifconfig command as shown
yoyok@yoyok-server:~$ ifconfig -a | grep eth0
eth0 Link encap:Ethernet HWaddr 00:13:d4:0e:32:59

Another application that can help identify all network interfaces available to your system is the lshw command. In the example below, lshw shows a single Ethernet interface with the logical name of eth0 along with bus information, driver details and all supported capabilities.

yoyok@yoyok-server:~$ sudo lshw -class network
[sudo] password for yoyok:
description: Ethernet interface
product: RTL-8139/8139C/8139C+
vendor: Realtek Semiconductor Co., Ltd.
physical id: 2
bus info: pci@0000:02:02.0
logical name: eth0
version: 10
serial: 00:13:d4:0e:32:59
size: 10MB/s
capacity: 100MB/s
width: 32 bits
clock: 33MHz
capabilities: pm bus_master cap_list ethernet physical tp mii 10bt 10bt-fd 100bt 100bt-fd autonegotiation
configuration: autonegotiation=on broadcast=yes driver=8139too driverversion=0.9.28 duplex=half latency=64 link=no maxlatency=64 mingnt=32 module=8139too multicast=yes port=MII speed=10MB/s

To configure your system to use a static IP address assignment, add the static method to the inet address family statement for the appropriate interface in the file /etc/network/interfaces. The example below assumes you are configuring your first Ethernet interface identified as eth0. Change the address, netmask, and gateway values to meet the requirements of your network.

auto eth0
iface eth0 inet static

By adding an interface configuration as shown above, you can manually enable the interface through
the ifup command.
sudo ifup eth0

To manually disable the interface, you can use the ifdown command.
sudo ifdown eth0

Loopback Interface
The loopback interface is identified by the system as lo and has a default IP address of It can be viewed using the ifconfig command.

yoyok@yoyok-server:~$ ifconfig lo
lo Link encap:Local Loopback
inet addr: Mask:
inet6 addr: ::1/128 Scope:Host
RX packets:2718 errors:0 dropped:0 overruns:0 frame:0
TX packets:2718 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:183308 (183.3 KB) TX bytes:183308 (183.3 KB)

By default, there should be two lines in /etc/network/interfaces responsible for automatically
configuring your loopback interface. It is recommended that you keep the default settings unless you have a specific purpose for changing them. An example of the two default lines are shown below.

auto lo
iface lo inet loopback

The Dynamic Host Configuration Protocol (DHCP) is a network service that enables host computers
to be automatically assigned settings from a server as opposed to manually configuring each network host. Computers configured to be DHCP clients have no control over the settings they receive from the DHCP server, and the configuration is transparent to the computer's user.
The most common settings provided by a DHCP server to DHCP clients include:
• IP-Address and Netmask

However, a DHCP server can also supply configuration properties such as:
• Host Name
• Domain Name
• Default Gateway
• Time Server
• Print Server

The advantage of using DHCP is that changes to the network, for example a change in the address of
the DNS server, need only be changed at the DHCP server, and all network hosts will be reconfigured the next time their DHCP clients poll the DHCP server. As an added advantage, it is also easier to integrate new computers into the network, as there is no need to check for the availability of an IP address. Conflicts in IP address allocation are also reduced.
A DHCP server can provide configuration settings using two methods:

MAC Address
This method entails using DHCP to identify the unique hardware address of each network card
connected to the network and then continually supplying a constant configuration each time the
DHCP client makes a request to the DHCP server using that network device.

Address Pool
This method entails defining a pool (sometimes also called a range or scope) of IP addresses from
which DHCP clients are supplied their configuration properties dynamically and on a "first come,
first served" basis. When a DHCP client is no longer on the network for a specified period, the
configuration is expired and released back to the address pool for use by other DHCP Clients.
Ubuntu is shipped with both DHCP server and client. The server is dhcpd (dynamic host
configuration protocol daemon). The client provided with Ubuntu is dhclient and should be installed on all computers required to be automatically configured. Both programs are easy to install and configure and will be automatically started at system boot.

At a terminal prompt, enter the following command to install dhcpd:
sudo apt-get install dhcp3-server
You will probably need to change the default configuration by editing /etc/dhcp3/dhcpd.conf to suit your needs and particular configuration.
You also need to edit /etc/default/dhcp3-server to specify the interfaces dhcpd should listen to. By default it listens to eth0.

# Sample /etc/dhcpd.conf
# (add your comments here)
default-lease-time 600;
max-lease-time 7200;
option subnet-mask;
option broadcast-address;
option routers;
option domain-name-servers,;
option domain-name "mydomain.example";
subnet netmask {

This will result in the DHCP server giving a client an IP address from the range or It will lease an IP address for 600
seconds if the client doesn't ask for a specific time frame. Otherwise the maximum (allowed) lease
will be 7200 seconds. The server will also "advise" the client that it should use as
its subnet mask, as its broadcast address, as the router/gateway and and as its DNS servers.


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  2. Wuiiih... kudu nyoba ngutak-atik server nih biar bisa. tp servernya siapa ya???

  3. @bangjlimz: hehehe ... ok
    @enthunk: kimia's server

  4. pesan linux warnet mas. aku punya 4 thin client dan 4 komputer. butuh linux untuk server thin client dan server komputer biasa + biling. silahkan hubungi saya