Configuring sub interfaces in RHEL6.

In the ‘Configuring IP on RedHat‘  post we considered about how to configure an ip-address to an interface in RHEL6. Now let’s move another step further and configure a sub interface. Sub interface is a logical interface which usually allows you to create VLANs.

In the below exercise I will create sub interfaces for the interface “eth0”.  I should provide that the file ‘ifcfg-eth0’ is already in my system, configured properly and given the ip-address ‘10.1.1.1’.

First you have to create a file in the same directory “/etc/sysconfig/network-scripts/” named in a specific format.

Format of the file (if the interface is eth0):

<Interface name> :  <sub interface number>
 Ex:          eth0:100

How to do that?

First go to the director ‘network-scripts’

#cd /etc/sysconfig/network-scripts/

Now you need to copy the ifcfg file you have for eth0 and rename it as ‘ifcfg-eth0:100’.

#copy ifcfg-eth0 ifcfg-eth0:100

Now you should do tiny adjustments to the newly created file in order to configure it as a sub-interface.

How to do that?

First open the file in vi editor,

#vi ifcfg-eth0:100

In my case file looks something like below,

DEVICE="eth0"HWADDR="08:00:27:4F:CF:22"NM_CONTROLLED = "no"ONBOOT="yes"IPADDR=10.1.1.1NETMASK=255.255.255.0

First rename the device into “eth0:100”

Then, modify the ip-address.

File will ultimately looks like this.

DEVICE="eth0:100"HWADDR="08:00:27:4F:CF:22"NM_CONTROLLED = "no"ONBOOT="yes"IPADDR=10.1.2.1NETMASK=255.255.255.0

Now save and quit.

Good, you have successfully configured the sub-interfaces and now it’s time to restart the network adapters. 

This can simply done by the command,

#/etc/init.d/network restart

Now check what you have done by using the ‘ifconfig’ command.

Make sure that you have an entry for the sub-interface ‘eth0:100’.

Thanks.