Making Linux a Router or Gateway

Here's an example of how to set up simple routing on a Linux box.

Setup:
A Linux box with two NICs
Two network switches
Two or more additional computers

1. Add this line to your /etc/sysctl.conf file and comment everything else out
net.ipv4.ip_forward = 1

2. Modify the following files in /etc/sysconfig/network-scripts

ifcfg-eth0
DEVICE=eth0
IPADDR=192.168.80.138
NETMASK=255.255.255.0
GATEWAY=192.168.80.1

ifcfg-eth1
DEVICE=eth1
IPADDR=192.168.49.132
NETMASK=255.255.255.0
GATEWAY=192.168.49.2

route-eth0
GATEWAY0=192.168.49.132
NETMASK0=255.255.255.0
ADDRESS0=192.168.49.0

route-eth1
GATEWAY0=192.168.80.138
NETMASK0=255.255.255.0
ADDRESS0=192.168.80.0

3. Setup your other machines so that their gateway is 192.168.49.132 or 192.168.80.138

Use the GUI in Windows or use the following command in Linux:
route add default gw 192.168.80.138

Test from windows client:
>ipconfig

Windows IP Configuration
IP Address. . . . . . . . . . . . : 192.168.80.142
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.80.138

>tracert 192.168.49.130

Tracing route to 192.168.49.130 over a maximum of 30 hops
1 1 ms <1 style="font-weight: bold;">