Basic Network Configuration of Linux System

Main configuration files

• /etc/hostname : contains name of host machine ; give the hostname in this file to permanently change the hostname. Otherwise, use "hostname" command to change the hostname temporarily

#hostname client1.ciscofriend.com

• /etc/hosts : Contains Name to IP mapping in the local system
• /etc/resolv.conf : Contains address of DNS servers
• /etc/nsswitch.conf : Determines order in which name resolution take place in system. We can change the order in this file  to configure  system to check first DNS then host file etc.

Redhat Network Files

• /etc/sysconfig/networks-scripts/ifcfg-eth0 : IP address information stored here
• /etc/sysconfig/network : This file contains the hostname; but this is a non standard way, Ubuntu/Debain is using the correct way

Debian/Ubuntu Network files

• /etc/network/interfaces

Commands to configure network

• Ifconfig : dipsplay and configure network interfaces

#ifconfig eth0 192.168.1.22  (set the IP of Ethernet 0 interface to 192.168.1.22)

#ifconfig eth0 netmask 255.255.255.0  (set the subnet mask)

#ifconfig eth0 hw ether 00:00:00:00:00:11 (To change the MAC address of eth0 interface)

#route add default gw 192.168.1.1  (To change the default gateway)

• Ifup : configure and activate network interface based on config files

#ifup eth0

• Ifdown- disable configured network interfaces

#ifdown eth0

Making CD/DVD as yum repository

1. Mount the CD/DVD to a folder

# mkdir /cdrom

# mount -t iso9660 -o ro /dev/cdrom /cdrom

2. Create a repository file for that folder in /etc/yum.repos.d/

# nano /etc/yum.repos.d/cdrom.repo

Now add the following content to the file and save the file

[cdrom]
name=CD repo
baseurl=file:///cdrom
gpgcheck=0

Now we can install software using the yum command

Disable login of all users except root

sudo touch /etc/nologin

Note: Now, only root can login to the system. Login as root and delete that file to allow other users to login

rm /etc/nologin

Network Time Protocol (NTP) configuration

One time update

If you want to synchronize with NTP server just now, then execute the following command:

$ sudo ntpdate 1.in.pool.ntp.org

Here 1.in.pool.ntp.org is the NTP server we are synchronizing with. You can find closer NTP server to your country from www.pool.ntp.org

NTP automatic synchronization through service

$ sudo apt-get install ntp

$ sudo service ntp start

If you want to synchronize with more closer NTP servers, then edit ntp.conf file by replacing the existing NTP servers with closer servers.

$ sudo nano /etc/ntp.conf

now change ntp servers if you want and save the file and restart the service

$ sudo service ntp restart

NOTE: if you are running other distributions than Ubuntu, then login as root and run the command without “sudo” in front of it

Installing GNS3 on CentOS 6.x/RHEL 6.x/Fedora 15

1. Login as root then do the following steps:
   yum install python python-devel xorg-x11-proto-devel libXext-devel gcc-c++ libXrender*


2. Download and install Qt
   #wget http://get.qt.nokia.com/qt/source/qt-everywhere-opensource-src-4.7.4.tar.gz
   #tar -xzf qt-everywhere-opensource-src-4.7.4.tar.gz
   #cd qt-everywhere-opensource-src-4.7.4
   #./configure -nomake examples -nomake demos -qt-gif -no-exceptions -debug -qt3support
   #gmake
   #gmake install
   #PATH=/usr/local/Trolltech/Qt-4.7.4/bin:$PATH
   #export PATH


3. Download and install sip
   #wget http://www.riverbankcomputing.co.uk/static/Downloads/sip4/sip-4.13.tar.gz
   #tar -xvf sip-4.13.tar.gz
   #cd sip-4.13.tar
   #python configure.py
   #make
   #make install


4. Download and install PyQt
   #wget http://ftp.pardus.org.tr/pub/source/2009/PyQt-x11-gpl-4.8.4.tar.gz
   #tar xvf PyQt-x11-gpl-4.8.4.tar.gz
   #cd PyQt-x11-gpl-4.8.4
   #python configure.py -q /usr/local/Trolltech/Qt-4.7.4/bin/qmake
   #make
   #make install


5. Download GNS3
   #wget http://downloads.sourceforge.net/project/gns-3/GNS3/0.7.4/GNS3-0.7.4-src.tar.gz
   #tar -xvf GNS3*.tar.gz && rm GNS3*.tar.gz
   #cd GNS3-0.7.4-src
   #mkdir Dynamips IOS Project Cache Temp


6. Download Dynamips depending up on OS (64-bit/32-bit)
   #cd dynamips
   #wget http://downloads.sourceforge.net/gns-3/dynamips-0.2.8-RC2-amd64.bin?download (for 64-bit OS)
   #wget http://downloads.sourceforge.net/gns-3/dynamips-0.2.8-RC3-community-x86.bin?download (for 32-bit OS)
   #chmod +x dynamips-0.2.8-RC2-amd64.bin (if we use 32-bit version, use the name of that file)


7. Creating Quick launch with gns3 icon
   #wget http://www.noahbeach.com/wp-content/uploads/2011/08/gns3.png
   Now right click on the panel and select add to panel > custom launcher > select the gns3 location and press on the icon button to locate the icon just downloaded. ok
   Now if we press that icon in the panel, gns3 will run...!!!