I am a new Linux user. How do I add a new or default gateway using route command on Linux operating systems? How can I use route command to show or set a new route on Linux based server or desktop system?

You can use any one of the following tool to add, display, delete Linux kernel routing table:

(a) route command : show / manipulate the IP routing table on Linux.
b) ip command : show / manipulate routing, devices, policy routing and tunnels on Linux.

Display your current routing table

Open the Terminal or login to server using ssh/console. Type the following command to display routing table:
# route
OR
# route -n
Sample outputs:


 Fig.01: Display routing table using route command


# ip route show
OR
# ip route list
Sample outputs:

Linux add a default route using route command

Route all traffic via 192.168.1.254 gateway connected via eth0 network interface:
# route add default gw 192.168.1.254 eth0

Linux add a default gateway (route) using ip command

Route all traffic via 192.168.1.254 gateway connected via eth0 network interface:
# ip route add 192.168.1.0/24 dev eth0

Verify newly added route ip in the Linux kernel routing table

To verify new routing table, enter:
# ip route list
OR
# route -n

Verify new route

Use the ping command to verify connectivity to your router or external network:
# ping your-router-ip-here
# ping your-ISPs-Gateway-ip-here
# ping 192.168.1.254
# ping www.cyberciti.biz

How do I make routing changes persistent across reboots?

To make route entry persistent in the Linux kernel routing table, you need to modify config file as per your Linux distributions.

RHEL/CentOS/Fedora/Scientific Linux persistent routing configuration

Edit /etc/sysconfig/network and set default gateway IP address:
# vi /etc/sysconfig/network
Sample outputs:
You can add additional static route for eth0 by editing /etc/sysconfig/network-scripts/route-eth0 file as follows:

10.0.0.0/8 via 10.10.29.65

The above config sets static routing for network 10.0.0.0/8 via 10.9.38.65 router.

Debian / Ubuntu Linux persistence static routing configuration

Edit /etc/network/interfaces file, enter:
# vi /etc/network/interfaces
Append the following in eth0 section:

up route add -net 192.168.1.0 netmask 255.255.255.0 gw 192.168.1.254
down route del -net 192.168.1.0 netmask 255.255.255.0 gw 192.168.1.254

Save and close the file.

Generic method to add persistent static routing on Linux

Edit /etc/rc.d/rc.local or /etc/rc.local, enter
# vi /etc/rc.local
Append the following line:

/sbin/ip route add 192.168.1.0/24 dev eth0

Fuente: http://www.cyberciti.biz