Changes Made by linuxconf

linuxconf should have made changes to add the definition for your new NIC to the /etc/sysconfig/network-scripts directory, and created (or modified) a file in this directory named after the eth device number you have added (for example, ifcfg-eth1).

Note 

The ifcfg-lo file in this directory is for the loopback device on your computer. Do not remove it.

linuxconf may have also made changes to the /etc/sysconfig/network file. It should have also added an "alias" to tell the Linux kernel which network driver module to associate with this eth device (if you are using a modular kernel) in the /etc/modules.conf file.

These changes are permanent, because the boot script /etc/rc.d/init.d/ network uses these files (on a Red Hat system) to know how to configure the NICs on your system.