Mastering IP Configuration on CentOS: Static, Dynamic, IPv4 & IPv6 Guide

Network Interface Overview

Use ifconfig or ip addr to list interfaces such as eth0 (or ens33 on CentOS 7), lo, and virbr0.

Configuration Files

Network scripts reside in /etc/sysconfig/network-scripts/. Each NIC has a file named ifcfg-INTERFACE (e.g., ifcfg-eth0, ifcfg-lo). Example content for a static IPv4/IPv6 configuration is shown.

# ifcfg-eth0
TYPE=Ethernet
DEVICE=eth0
NAME=eth0
UUID=b4701c26-8ea8-46a5-b738-1d4d0ca5b5a9
ONBOOT=yes
BOOTPROTO=static
IPADDR=192.168.1.188
PREFIX=24
GATEWAY=192.168.1.1
DNS1=192.168.0.1
IPV6INIT=yes
IPV6ADDR=2001:250:250:250:250:250:250:222/64
IPV6_DEFAULTGW=2001:250:250:250::1
IPV6_AUTOCONF=no
IPV6_FAILURE_FATAL=no

Enable IPv6 Autoconfiguration

IPv4 uses DHCP by default. To enable IPv6, edit /etc/sysconfig/network and ensure the following lines are present:

NETWORKING=yes
NETWORKING_IPV6=yes
HOSTNAME=localhost.localdomain

Then set IPV6INIT=yes in the relevant ifcfg-INTERFACE file and restart the network service.

Static IP Configuration

For a permanent IPv4 address, include at least the following keys in ifcfg-INTERFACE:

TYPE=Ethernet

DEVICE=eth0

BOOTPROTO=static

ONBOOT=yes

IPADDR=192.168.1.188

PREFIX=24

(or NETMASK=255.255.255.0)

GATEWAY=192.168.1.1

DNS1=192.168.0.1

For IPv6, add the corresponding entries:

IPV6INIT=yes

IPV6ADDR=2001:250:250:250:250:250:250:222/64

IPV6_DEFAULTGW=2001:250:250:250::1

IPV6_AUTOCONF=no

IPV6_FAILURE_FATAL=no

Temporary (Non‑persistent) Address Assignment

Assign an IPv4 address for the current session:

ifconfig eth0 192.168.5.18 up
ip addr add 192.168.5.18/24 dev eth0

Assign an IPv6 address for the current session:

ifconfig eth0 inet6 add 2001:250:250:250:250:250:250:222/64

These settings disappear after a reboot or when the interface is restarted.

Common Management Commands

Show interfaces: ifconfig or ip addr Restart network service:

CentOS 7: systemctl restart network CentOS 6: service network restart Test connectivity:

IPv4: ping -I eth0 192.168.5.18 IPv6:

ping6 -I eth0 2001:250:250:250:250:250:250:222

Verification

After making changes, verify the configuration with ifconfig (or ip addr) and use the ping commands above to confirm reachability.