Static IP Configuration on CentOS 6

Introduction

There are two methods to assign network configuration to a device on the net. DHCP or static assignment. DHCP is normally set as default. Static configurations usually need IP addresses as well as DNS resolvers plus routing. In this tutorial, I will cover Linux static configuration on CentOS 6.

Prerequisites

• A shell editor like vi, nano or joe. We personally prefer vi.
• A Cloud VPS or Dedicated Server with CentOS 6 installation.

Step 1: Backup and Apply changes

The first step is to make a backup of your original file and then make the changes.

< id="docs-internal-guid-deea88ad-b7b1-f166-60cf-0e3775e92120">mv  /etc/sysconfig/network-scripts/ifcfg-eth0  /etc/sysconfig/network-scripts/ifcfg-eth0.bak
vi /etc/sysconfig/network-scripts/ifcfg-eth0

You can make changes like:

#My IP description
# IPv-4 DEVICE="eth0"
NM_CONTROLLED="yes"
ONBOOT=yes
HWADDR=20:89:84:c8:12:8a
TYPE=Ethernet
BOOTPROTO=static
NAME="System eth0"
UUID=5fb06bd0-0bb0-7ffb-45f1-d6edd65f3e03
IPADDR= 2001:db8::c0ca:1eaf
NETMASK=255.255.255.0

Note: Only two lines need to be changed, IPADDR and NETMASK. For IPv6 the following entries need to be added:

vi /etc/sysconfig/network
[...]
NETWORKING_IPV6=yes vi /etc/sysconfig/network-scripts/ifcfg-eth0
[...]
#IPv-6
IPV6INIT=yes
IPV6ADDR=2001:db8::c0ca:1eaf
IPV6_DEFAULTGW=2001:db8::1ead:ed:beef

Step 2: configuring DNS

We are going to use the following file to add the DNS /etc/resolv.conf

vi /etc/resolv.conf
[...]
PrefferredDNS 89.207.128.252
AlternateDNS 89.207.130.252

Additional nameserver lines can be added in case the first is not reachable.

Step 3: Editing your hostname

My hostname is myserver.sample.com You need to edit /etc/hosts file:

vi /etc/hosts
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
192.168.0.100 myserver.sample.com myserver ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6

and the resolv.conf file:

vi /etc/resolv.conf
NETWORKING=yes
HOSTNAME= myserver.sample.com GATEWAY=192.168.0.1
[...]

Step 4: Rebooting the server

To reboot the server:

reboot

Step 5: Checking the hostname

If you want to check the hostname after the reboot, you use this command:

hostname

If you want to have multiple IP addresses by creating an alias for eth0:0, create the following file:

vi /etc/sysconfig/network-scripts/ifcfg-eth0:0
#IP Aliasing DEVICE="eth0:0"
BOOTPROTO="static"
HWADDR=20:89:84:c8:12:8a
NM_CONTROLLED="no"
ONBOOT="yes"
TYPE="Ethernet"
IPADDR=192.168.0.109 NETMASK=255.255.255.0
GATEWAY=192.168.0.1
DNS1=8.8.8.8
DNS1=8.8.4.4

You should use your own IP. We have used 192.168.0.109 for IP aliasing. Restart the network services by this command:

/etc/init.d/network restart

You need to check all the changes that you have made:

ifconfig

The output should be similar to:

root@myserver:~# ifconfig
eth0 Link encap:Ethernet HWaddr 20:89:84:c8:12:8a
inet addr:192.168.0.100 Bcast:192.168.0.255 Mask:255.255.255.0
inet6 addr: 2001:db8::c0ca:1eaf/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:200197 errors:0 dropped:67 overruns:0 frame:0
TX packets:69689 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:64103748 (64.1 MB) TX bytes:14106191 (14.1 MB) eth0:0 Link encap:Ethernet HWaddr 20:89:84:c8:12:8a
inet addr:192.168.0.109 Bcast:192.168.0.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
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:65536 Metric:1
RX packets:10365 errors:0 dropped:0 overruns:0 frame:0
TX packets:10365 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:875114 (875.1 KB) TX bytes:875114 (875.1 KB)

Conclusion

Congratulations, you have successfully configured static IP on CentOS 6.