Hi,
Your server act as a Gateway machine , it means your server have 2 NIC.
If your structure is as follow:

WAN IP

|

|

----------------NIC A------------------

| LINUX BOX |

-------------NIC B --------------------

|

|
intranet

suppose NIC (eth0)--- A ---- have a WAN IP such as AAA.AAA.AAA.AAA
NIC (eth1)----B ------have a Local class C IP such as 192.168.1.0-524 (range )
then if you want to write/set routing table then pls do as following :

vi /etc/sysconfig/network-script/ifcfg-eth0

DEVICE=eth0
BOOTPROTO=static
HWADDR=xxxxxxxxxx
IPADDR=AAA.AAA.AAA.AAA
GATEWAY=routers' another end IP which is connected to outside of world (WAN IP)
NETMASK=255.255.255.248
ONBOOT=yes
TYPE=Ethernet

vi /etc/sysconfig/network-script/ifcfg-eth1

DEVICE=eth0
BOOTPROTO=static
HWADDR=xxxxxxxxxx
IPADDR=192.168.1.254
GATEWAY=AAA.AAA.AAA.AAA
NETMASK=255.255.255.0
ONBOOT=yes
TYPE=Ethernet



And if your machine have a single NIC then

vi /etc/sysconfig/network-script/ifcfg-eth1

DEVICE=eth0
BOOTPROTO=static
HWADDR=xxxxxxxxxx
IPADDR=192.168.1.254
GATEWAY=AAA.AAA.AAA.AAA
NETMASK=255.255.255.0
ONBOOT=yes
TYPE=Ethernet

and add DEFAULT routing table as follow

1.route add default gw AAA.AAA.AAA.AAA(WAN IP )