Basic Network Configuration in Linux

This network configuration guide is based on Fedora.

Configuration Tools

Text console configuration tool:

  • /usr/sbin/system-config-network-tui
  • /sbin/ifconfig

Using ifconfig:

  • ifconfig – display running network configuration
  • ifconfig -a – display all (running or not running network device) network configuration
  • ifconfig <interface> up – bring up the specified interface network
  • ifconfig <interface> down – bring down the specified interface network
  • ifconfig eth0 192.168.1.188 netmask 255.255.255.0 – setup a network interface with a specific IP address and sub-net mask
  • For further usage check #man ifconfig

Network Configuration Files

/etc/sysconfig/network – Defines your network and some of its characteristics.

The settings are:

  • NETWORKING=yes
  • HOSTNAME=localhost.localdomain

/etc/sysconfig/network-scripts/ifcfg-eth* – This is a configuration file for each network interface card. For eth0 the path would be /etc/sysconfig/network-scripts/ifcfg-eth0

The settings are permanent; some of the entries are shown below:

  • DEVICE=eth0
  • HWADDR=00:03:10:22:45
  • #For permanent fixed IP address
  • IPADDR=192.168.1.100
  • NETMASK=255.255.0.0
  • ONBOOT=yes
  • BOOTPROTO=none

/etc/networks – Provides a database of network names with network addresses similar to the /etc/hosts file.

The settings are:

  • Default 0.0.0.0
  • Loopback 127.0.0.1
  • Link-local 169.254.0.0

/etc/hosts – Defines local hosts.

The settings are:

  • 127.0.0.1  localhost  localhost.localdomain
  • 192.168.1.100  mymachine.mycompany.com mymachine

/etc/host.conf – Specifies order to search for host name for name resolution.

The settings are:

  • Multi on
  • Order hosts, bind

/etc/resolv.conf – Contains the address of name server

The settings are:

  • Nameserver your.isp.name.server

Configuring Ethernet Manually

Fixed IP

  • Ifconfig to set IP address and bring up the network card

#ifconfig eth0 192.168.1.188 netmask 255.255.255.0 up

  • To setup the network routing

#route add -net 192.168.0.0 netmask 255.255.255.0 eth0

  • Use route add or ip to add default gateway

#route add default gw 192.168.1.1 eth0

  • DNS for the network

Add “nameserver 218.186.1.88” at /etc/resolve.conf

  • Note: Please note that the above measure is temporary. To permanently set ip address, gateway and dns use system-config-network-tui.
  • Once you set fixed IP, netmask, gateway and DNS. The information will be recorded in etc/sysconfig/network-scripts/ifcfg-eth* as follows;
    • DEVICE=eth0
    • HWADDR=00:05:20:15:36
    • #For permanent fixed IP address
    • IPADDR=192.168.1.100
    • NETMASK=255.255.0.0
    • ONBOOT=no
    • BOOTPROTO=none
  • Note: If you have hard coded fixed IP in the config file ifcfg-eth*, if you type #ifconfig eth0 up, it will not configure the fix IP from the file, the eth0 is up with no address assigned.
  • Therefore, a proper way to completely bring up and down the network interface card (NIC) is to use #ifup and #ifdown instead of ifconfig.
  • If eth0 is down for some reason, using #ifup eth0 will turn on the NIC with all address, gatway and DNS configure in the file
  • The console utility (system-config-network-tui) do not have the ability to set the configuration such that eth0 is turn on during startup, to do this we must manually change to ONBOOT=yes.
  • If eth0 still will not turn on during startup; this is because the service network is not turn on.
  • To turn on the network service during startup, use the command #service network start
  • To permently turn on the network service #chkconfig network on

DHCP Client

  • If inside the file ifcfg-eth0,the entry ‘BOOTPROTO = none’ or there is no entry on BOOTPROTO use the following:
    • #ifup eth0
    • #dhclient
  • If inside the file ifcfg-eth0, the entry ‘BOOTPROTO = dhcp’ use the following:
    • #ifup eth0
  • Note: To configure BOOTPROTO just run the utilities system-config-network-tui
  • However, the console utility do not have the ability to set the configuration such that eth0 is turn on during startup, to do this we must manually change the file etc/sysconfig/network-scripts/ifcfg-eth*; ONBOOT=yes
  • Then make sure service Network is started and set to turn on permanently with the command #chkconfig network on

Alternative method of starting network

  • Add the following at /etc/rc.d/rc.local
    • # ifup eth0
  • or
    • # dhclient eth0
  • Note: Using local startup script, there is no need to turn on network services

Network Manager (New)

  • A new way of managing network is to install the package NetworkManager which does the management of network automatically.
  • NetworkManager is designed to replace all other network configuration. It includes all types of network from Ethernet to wireless network.
  • Use the command #yum install NetworkManager
  • Using NetworkManager, you still need tp ensure that the settings for eth* is setup properply. You need to ensure that ONBOOT=yes.

End.

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