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Linux Network Configuration

This article covers network configuration on Linux, with specific reference to the information needed for the RHCSA EX200 and RHCE EX300 certification exams.

Remember, the exams are hands-on, so it doesn't matter which method you use to achieve the result, so long as the end product is correct.

Related articles.

Networking Files

The "/etc/sysconfig/network" file holds top-level networking configuration, including the hostname and gateway settings.

# cat /etc/sysconfig/network
NETWORKING=yes
HOSTNAME=rhce1.localdomain
GATEWAY=192.168.122.1
#

The "/etc/sysconfig/network-scripts/ifcfg-eth0" file holds the network configuration for the "eth0" adapter. If you have multiple network adapters, you would expect additional configuration files (eth1, eth2 etc.). The following example contains the configuration for a DHCP adapter.

# cat /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE="eth0"
NM_CONTROLLED="yes"
ONBOOT=yes
TYPE=Ethernet
BOOTPROTO=dhcp
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
NAME="System eth0"
UUID=5fb06bd0-0bb0-7ffb-45f1-d6edd65f3e03
HWADDR=52:54:00:91:6A:B3
PEERDNS=yes
PEERROUTES=yes
#

The following example is for a static IP address.

# cat /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE=eth0
NM_CONTROLLED=yes
ONBOOT=yes
TYPE=Ethernet
BOOTPROTO=none
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
NAME="System eth0"
UUID=5fb06bd0-0bb0-7ffb-45f1-d6edd65f3e03
HWADDR=52:54:00:91:6a:b3
PEERROUTES=yes
IPADDR=192.168.122.89
NETMASK=255.255.255.0
GATEWAY=192.168.122.1
DNS1=192.168.122.1
USERCTL=no
#

The "/etc/hosts" file contains information for local name resolution.

# cat /etc/hosts
127.0.0.1      localhost localhost.localdomain localhost4 localhost4.localdomain4
192.168.122.89 rhce1.localdomain rhce1
#

The "/etc/resolv.conf" file is used to configure the location of the DNS servers to be used for name resolution. There can be multiple "nameserver" lines, one for each nameserver.

# cat /etc/resolv.conf
# Generated by NetworkManager
search localdomain
nameserver 192.168.122.1
#
The "/etc/sysconfig/network-scripts" directory contains a number of network related scripts and commands. The ifdown and ifup commands are used to stop and start the specified network adapters.
# ifdown eth0
Device state: 3 (disconnected)
# ifup eth0
Active connection state: activated
Active connection path: /org/freedesktop/NetworkManager/ActiveConnection/5
#

The current network settings are displayed using the ifconfig command.

# ifconfig -a
eth0      Link encap:Ethernet  HWaddr 52:54:00:91:6A:B3  
          inet addr:192.168.122.89  Bcast:192.168.122.255  Mask:255.255.255.0
          inet6 addr: fe80::5054:ff:fe91:6ab3/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:13548 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6144 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:2871500 (2.7 MiB)  TX bytes:824754 (805.4 KiB)
          Interrupt:11 Base address:0xe000 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:48 errors:0 dropped:0 overruns:0 frame:0
          TX packets:48 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:3230 (3.1 KiB)  TX bytes:3230 (3.1 KiB)

#

system-config-network-tui

The system-config-network-tui and system-config-network commands start a text-based network configuration tool.

Network - TUI

Navigate using the "tab", "arrow" and "return" keys. The "Device configuration" option gives a list of network devices.

Network - TUI Devices

Selecting the device allows you to edit the adapter's network configuration, which is saved to the "/etc/sysconfig/network-scripts/ifcfg-eth0" file.

Network - TUI eth0

The "DNS configuration" option on the first screen allows you to modify the configuration in the "/etc/sysconfig/network" and "/etc/resolv.conf" files.

Network - TUI DNS

The network configuration can also be initiated using the setup command.

Network Connections

The "Network Connections" dialog is available from the menu (System > Preferences > Network Connections) at the console.

Network - Network Connections

Highlighting the device and clicking the "Edit" button allows you to view or alter the configuration of a device.

Network - Network Connections eth0

For more information see:

Hope this helps. Regards Tim...

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