Configuring virtual network interfaces in Linux

Introduction

For the Debian based system

Did you know that you can assign more that one IP address to a single physical network interface? This technique is quite useful, for example when working with Apache and virtual hosts, as it allows you to access same Apache server by using two different IP addresses.

Temporary virtual network interface

ifconfig

check network interface name and then add

Replace enp2s0 as per your network interface name

sudo ifconfig enp2s0:0 219.91.251.164

Making the Interface permanent

These interfaces are temporary that means it will not last after reboot so to make it persistent we need to add it in

sudo vi /etc/network/interfaces

iface eth0:0 inet static
address 219.91.251.164
netmask 255.0.0.0
broadcast 123.255.255.255

For redhat based system

From the above output we can see that currently we have configured eth0 network interface only. Next, we are going to locate a corresponding network interface configuration file for eth0:

# grep -l DEVICE.*eth0 /etc/sysconfig/network-scripts/*

The configuration file responsible for the eth0 network interface is /etc/sysconfig/network-scripts/ifcfg-eth0

[root@rhel7 ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth0 
DEVICE="eth0"
NETBOOT="yes"
HWADDR="08:00:27:15:38:B7"
TYPE="Ethernet"
BOOTPROTO="none"
NAME="eth0"
UUID="462f4834-4fe7-43a7-84e7-83b2722e94c1"
ONBOOT="yes"
IPADDR="10.1.1.110"
NETMASK="255.0.0.0"
GATEWAY="10.1.1.1"

In order to create a virtual network interface we can first copy a master configuration file /etc/sysconfig/network-scripts/ifcfg-eth0 and then edit its content to set an appropriate network interface name and IP address:

[root@rhel7 ~]# cd /etc/sysconfig/network-scripts/
[root@rhel7 ~]# cp ifcfg-eth0 ifcfg-eth0:0
[root@rhel7 ~]# cp ifcfg-eth0 ifcfg-eth0:1

Next, we need to edit DEVICE, NAME, IPADDR in both virtual network configuration files. Below you can see both edited configuration files:

on Sysvinit

2. Bringing interfaces up/down

Two methods can be used to bring interfaces up or down.

2.1. Using "ip"

Usage:

# ip link set dev <interface> up
# ip link set dev <interface> down

Example:

# ip link set dev eth0 up
# ip link set dev eth0 down

2.2. Using "ifconfig"

Usage:

# /sbin/ifconfig <interface> up
# /sbin/ifconfig <interface> down

Example:

# /sbin/ifconfig eth0 up
# /sbin/ifconfig eth0 down