If you want to configure networking in CentOS Desktop by using command line utilities, you should be aware that networking on CentOS Desktop is by default managed by a daemon with GUI interface, which is called NetworkManager. This means that whenever you want to change network configuration, you are supposed to do so via NetworkManager. Any change made otherwise will be lost or overwritten by NetworkManager later.
So the first step to configuring networking using command line on CentOS Desktop is to disable NetworkManager, and enable network service.
To disable NetworkManager permanently on CentOS, do the following.
$ sudo chkconfig NetworkManager off
Then, activate network service instead.
$ sudo chkconfig network on
Once NetworkManager is disabled, you can now configure networking simply by editing files in /etc/sysconfig/network-script, as described in the post.
When you are done with configuring all existing interfaces, restart network to activate the change.
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