How to temporarily add an IP alias on Linux

[Leon van Heerden]

Sometimes you need to be able to access multiple IP ranges from the same Linux box.
Rather than setting the IPs manually, you can add an alias on the fly.

If you run the ifconfig command, it will display your current IP.

Code: Select all

ifconfig

The output will look something like this

Code: Select all

eth0      Link encap:Ethernet  HWaddr 00:0f:fe:46:12:34 
          inet addr:192.168.0.10  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::20f:feff:fe46:6203/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:17694 errors:0 dropped:0 overruns:0 frame:0
          TX packets:5986 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:1722566 (1.7 MB)  TX bytes:3282006 (3.2 MB)
          Interrupt:17


You will see the IP address next to the entry that says "inet addr".

if you have root access you can run the following command to add an alias "eth0:1" to the current "eth0".

Code: Select all

ifconfig eth0:1 192.168.50.10

This will add the alias "eth0:1" and assign the IP address 192.168.50.10 to it.
When you now run "ifconfig" you will see an additional interface entry with the new IP.

Code: Select all

eth0:1    Link encap:Ethernet  HWaddr 00:0f:fe:46:62:03 
          inet addr:192.168.50.10  Bcast:192.168.50.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:17


You can now access other PCs on your local LAN that has n IP in the 192.168.50.* range.

To remove the alias again, you can run the following command.

Code: Select all

ifconfig eth0:1 down

NOTE:Be very carefull with this command since you could bring down the entire network connection for the server, if you misspell this command.