How to Configure Default Route on Cisco Router

In any network, routers play the role of forwarding traffic from one network to another. They make decisions about where to send data packets based on routing tables, which contain information about known networks and the best paths to reach them.
One important concept in routing is the default route, also known as the gateway of last resort. When a router receives a packet for which it does not have a route to the destination in its routing table, it normally forwards the traffic to the default route. However, if the default route is not configured on the router, it will simply drop the packet.
Usually, in a network, the default route is configured to direct traffic to the internet. This means that any traffic for which the destination route does not exist in the routing table of a router will be forwarded to the internet.
In this blog post, I will show you how to configure the default route on a Cisco router using a sample network topology.

Network Topology

In this post, we’ll work with a simple network comprising three routers: R1, R2, and R3. Our objective is to configure default routes strategically across these routers to optimize traffic flow within the network.

In this demonstration, we’ll configure the default routes on each router as follows:

• R1’s default route will use the e0/0 interface of R2.
• R2’s default route will use the e0/1 interface of R3.
• R3’s default route will use the e0/1 interface of R2.

How to Configure Default Route on Cisco Router

Here are the steps to configure the default route on a Cisco router using the network topology given above as an example

Step 1: Configure the interface of the routers

The first step is to assign an IP address to the interfaces of the router. Enter the following commands on each of the routers to do this:

Router 1

R1(config)#interface ethernet0/0
R1(config-if)#ip address 192.168.12.1 255.255.255.0
R1(config-if)#no shutdown
R1(config-if)#exit
R1(config)#interface loopback 0
R1(config-if)#ip address 1.1.1.1 255.255.255.0
R1(config-if)#no shutdown
R1(config-if)#exit

Router 2

R2(config)#interface ethernet0/0
R2(config-if)#ip address 192.168.12.2 255.255.255.0
R2(config-if)#no shutdown 
R2(config-if)#exit

R2(config)#interface ethernet0/1
R2(config-if)#ip address 192.168.21.1 255.255.255.0 
R2(config-if)#no shutdown 
R2(config-if)#exit

R2(config)#interface loopback 0
R2(config-if)#ip address 2.2.2.2 255.255.255.0
R2(config-if)#no shutdown 
R2(config-if)#exit

Router 3

R3(config)#interface ethernet0/1
R3(config-if)#ip address 192.168.21.2 255.255.255.0
R3(config-if)#no shutdown 
R3(config-if)#exit

R3(config)#interface loopback 0
R3(config-if)#ip address 3.3.3.3 255.255.255.0
R3(config-if)#no shutdown 
R3(config-if)#exit

Step 2: Configure Default route on the routers

Just like stated before, the default route is the route a router will forward traffic to if there is no route to the destination of traffic in its routing table.
Here are the commands configure the default route on each of the routers as specified in the objective above.

Router 1

R1(config)#ip route 0.0.0.0 0.0.0.0 192.168.12.2

Here is a brief explanation of the above command;

• ip route: This keyword indicates that we are configuring a static IP route.
• 0.0.0.0 0.0.0.0: This specifies the destination network and subnet mask. In the context of a static route, 0.0.0.0 with a subnet mask of 0.0.0.0 represents the default route, which means all packets with destinations not explicitly listed in the routing table will be forwarded to the next-hop address specified in the command.
• 192.168.12.2: This is the next-hop IP address where packets should be sent if their destination matches the default route

Router 2

R2(config)#ip route 0.0.0.0 0.0.0.0 192.168.21.2
R2(config)#ip route 1.1.1.0 255.255.255.0 192.168.12.1

Router 3

R3(config)#ip route 0.0.0.0 0.0.0.0 192.168.21.1

Step 3: Verify the configuration

To verify that the configuration is working, from the user Exec mode of one of the routers, ping an IP address that you know does not exist on the routing table. If you receive a reply, the default route configuration was done properly.

Related Posts

Static Route Configuration in Cisco Router

How To Configure Static Route On Cisco Layer 3 Switch in Packet Tracer

Reference: https://github.com/misterkrittin/CCNA-Labs