1/ RedHat based system use the file /etc/sysconfig/network to read the saved hostname at system boot. This is set using the init script /etc/rc.d/rc.sysinit
nano /etc/sysconfig/network
NETWORKING=yes
HOSTNAME="plain.domainname.com"
GATEWAY="111.222.333.1"
GATEWAYDEV="eth0"
FORWARD_IPV4="yes"
2/ TCP/IP Network Configuration Files
This configures Linux so that it knows which DNS server will be resolving domain names into IP addresses
nano /etc/resolv.conf
search name-of-domain.com - Name of your domain or ISP's domain if using their name server
nameserver XXX.XXX.XXX.XXX - IP address of primary name server
nameserver XXX.XXX.XXX.XXX - IP address of secondary name server
3/ Locally resolve node names to IP addresses
nano /etc/hosts
::1 localhost6.localdomain6 localhost6
# Do not remove the following line, or various programs
# that require network functionality will fail.
111.222.333.444 yourname.server.com yourname
127.0.0.1 localhost
4/ Configuration settings for your first ethernet port
nano /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE=eth0
BOOTPROTO=static
BROADCAST=111.222.333.255
IPADDR=111.222.333.444
NETMASK=255.255.255.0
NETWORK=111.222.333.0
ONBOOT=yes
And to finalize , you need to restart your network
service network restart
