Types of Routing and Types of Routes Explained

A router connects different networks. It works as an intermediate device. It has multiple interfaces. When it receives a data packet on an interface, it reads the packet's destination address, makes the forwarding decision, selects the forwarding interface based on the forwarding decision, and forwards the packet from the selected interface. This process is known as routing. The information it uses to make the forwarding decision is called the routing information. It saves routing information in the routing table.

Routing information includes paths and related information of connected devices on all interfaces. A path is called a route. A router can have a single, multiple, or no route to a destination. If it has only one route to a destination, it uses that route to forward incoming packets intended for that destination. If it has multiple routes, it selects the best route. If there is no route, it discards the packets.

There are three ways to add routing information to the routing table.

1. Automatic
2. Static or Manual
3. Dynamic

Automatic

In this method, a router automatically adds the routing information. It uses the IP configuration of the active interfaces to build the routing information. When the administrator changes the IP configuration or the interface's state, the router automatically updates the related information in the routing table. Since automatic routing uses IP configurations of local interfaces, it cannot add routes available on other routers. You can use it in a network that has only one router. The following image shows an example network where you can use it.

A network with multiple routers requires a static or dynamic routing method.

Manual or static

In this method, the administrator manages the routing information. He manually adds routing information to the routing table. If any change occurs in the network, he has to update the related information in the routing table. It is a good option if the network size is small. The following image shows an example network where you can use it.

Dynamic

In this method, the administrator configures a routing protocol on the router. The routing protocol automatically adds and manages the routing information in the routing table. If any change occurs in the network, it automatically updates the related information in the routing table. It is a good option if the network size is large. The following image shows an example network where you can use it.

Differences between automatic, manual, and dynamic routing methods

The following table lists the differences between automatic, manual, and dynamic routing methods.

Types of routes

Routing methods add route information to the routing table. We can categorize the route based on the method that adds it to the routing table, such as local, connected, static and dynamic.

The automatic routing method adds connected routes and local routes to the routing table. It calculates these routes from the IP configuration of active interfaces. The routing table uses codes C and L to show connected and local routes.

The static or manual routing method adds static routes to the routing table. An administrator manually creates and adds these routes to the routing table. The routing table uses the code S to show static routes.

The dynamic routing method adds dynamic routes to the routing table. A routing protocol learns and adds these routes to the routing table. Dynamic routes are further classified based on the routing protocols. Each routing protocol uses a different code to show its routes in the routing table. To view the code for each route type, you can use the 'show ip route' command. The following image shows the output of this command.

Conclusion

Routing information contains information about all known routes in the network. Routers save routing information in the routing table. There are three ways to add and manage routing information. These methods are automatic, manual, and dynamic. In the automatic routing method, the router automatically adds and manages it. In the static routing method, the administrator manually does this job. In the dynamic routing method, the administrator configures a routing protocol, and that protocol does it.