if you need to make changes to your network you can use the file located at /etc/sysconfig/network-scripts/ifcfg-eth0 - this is an example file how it should look like if you need to manually change your ip address or your default gateway on your linux system

[root@ns11 network-scripts]# cat ifcfg-eth0
# Broadcom Corporation NetXtreme BCM5703X Gigabit Ethernet
DEVICE=eth0
BOOTPROTO=static
BROADCAST=192.168.1.255
HWADDR=00:0B:CD:FF:38:FF
IPADDR=192.168.1.101
IPV6INIT=yes
GATEWAY = 192.18.1.1
IPV6_AUTOCONF=yes
NETMASK=255.255.255.224
NETWORK=192.168.1.0
ONBOOT=yes