GIT – aliasing is the process of assigning more than one address to a network interface. This is useful for Apache web virtual hosting or other network servers such as .

This tutorial explains how to assign one or more IP address to a single network interface under operating system.

It is possible to create network alias or assign 2 ip address to a single NIC under FreeBSD operating system.

Our Sample Setup

  • Interface name: lnc0 – IP : 192.168.1.1/255.255.255.0
  • Interface name: lnc0 alias – IP : 192.168.1.5/255.255.255.255

Netmask must be different otherwise you will get an error ifconfig: ioctl (SIOCAIFADDR): File exists.

Set ip alias using ifconfig line utility

Login as the user.

Now, use ifconfig command as follows to set alias:
# ifconfig lnc0 192.168.1.5 netmask 255.255.255.255 alias

Persistent IP Alias Configuration

Edit file /etc/rc.conf to setup persistent ip aliasing option by appending following configuration, so that next time FreeBSD comes up (after restart/shutdown) it will create alias for you:
ifconfig_lnc0_alias0="192.168.1.5 netmask 255.255.255.255"

Finally, Restart FreeBSD network service using network restart script:
# /etc/rc.d/netif restart && /etc/rc.d/routing restart
Display alias and real ip using ifconfig lnc0 command:
# ifconfig lnc0
Sample output:

lnc0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
inet6 fe80::20c:29ff:fe01:ddbd%lnc0 prefixlen 64 scopeid 0x1
inet 192.168.1.2 netmask 0xffffff00 broadcast 192.168.1.255
inet 192.168.1.5 netmask 0xffff

Sample /etc/rc.conf file with IP aliasing

Here is my /etc/rc.conf file with em0 and em1 interface with 5 aliases:

hostname="sun.nixcraft.in"
# default vsnl router interface
defaultrouter="202.54.1.200"
# Force 10Mbps for both public and private LAN interace
ifconfig_em0="inet 10.20.110.2 netmask 255.255.255.192 media 10baseT/UTP mediaopt full-duplex"
ifconfig_em1="inet 202.52.1.2 netmask 255.255.255.248 media 10baseT/UTP mediaopt full-duplex"
ifconfig_em0_alias0="inet 10.20.1.226 netmask 255.255.255.0"
ifconfig_em0_alias1="inet 10.20.1.227 netmask 255.255.255.0"
ifconfig_em0_alias2="inet 10.20.1.228 netmask 255.255.255.0"
ifconfig_em0_alias3="inet 10.20.1.229 netmask 255.255.255.0"
ifconfig_em0_alias4="inet 10.20.1.230 netmask 255.255.255.0"
# static routing configuration
static_routes="lan0"
route_lan0="-net 10.0.0.0/8 10.20.110.1"

Further readings:

  • Read ifconfig man page.
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