Network interface settings – CentOS

Configuration of the “/etc/sysconfig/network-scripts/ifcfg-eth0” file

In this file, you would find your basic network device configuration. Here, ifcfg-eth0 is the first Ethernet device; ifcfg-eth1 would be the second Ethernet NIC (network interface card), and so forth. In this file, you can have quite a few settings.

Directives Required / Optional Expected Settings Comment
DEVICE= Required ethX You must have this entry specifying the Linux device name.
ONBOOT= Optional yes / no Start the device on boot? This will default to yes.
BOOTPROTO= Required static / dhcp / none Static hard set our IP, or do we want a dhcp assignment? “dhcp”, “none” is the same as static.
IPADDR= Optional IP address of machine The address we want if we are setting a static IP for the interface.
NETMASK= Optional Subnet mask Required for static IPs. The subnet mask.
NETWORK= Optional Network address Recommended for static IPs. The network that we are on.
BROADCAST= Optional Network broadcast address Recommended for static IPs. The broadcast address.
HWADDR= Optional Device MAC address The MAC address of our network card. Normally provided by the Anaconda installer at install time.
USERCTL= Optional yes / no Allow normal non-administrative user to take down and bring up the device. Defaults to “no”.
GATEWAY= Optional IP address of gateway The network gateway IP address.

Not all of these are necessary for proper operation, and the order they are in is irrelevant. I prefer to specify the additional directives of NETWORK and BROADCAST in my /etc/sysconfig/network-scripts/ifcfg-eth0 on machines that I want to have a hard-set IP address, mainly servers of any sort. If you want to use a DHCP-assigned address, your /etc/sysconfig/network-scripts/ifcfg-eth0 file would look something like this:

# Advanced Micro Devices [AMD] 79c970 [PCnet32 LANCE]
DEVICE=eth0
BOOTPROTO=dhcp
HWADDR=08:00:27:4B:3B:06
ONBOOT=yes
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