What is Routing? Types of Routing and How does it take place

In this article, you’ll learn about What is Routing? Types of Routing, How does it take place and more.

What is Routing?

Network routing is the process of selecting a path across one or more networks. The principles of routing can apply to any type of network, from telephone networks to public transportation. In packet-switching networks, such as the Internet, routing selects the paths for Internet Protocol (IP) packets to travel from their origin to their destination. These Internet routing decisions are made by specialized pieces of network hardware called routers.

Routing Metrics and Costs

Router metrics are metrics used by a router to make routing decisions. A metric is typically one of many fields in a routing table. Router metrics help the router choose the best route among multiple feasible routes to a destination. The route will go in the direction of the gateway with the lowest metric.

A router metric is typically based on information such as path length, bandwidth, load, hop count, path cost, delay, maximum transmission unit (MTU), reliability, and communications cost.

1. Path Length: In this, the administrator will assign costs to each path (between two nodes). The path length will be the sum of all the path costs. The path with the less path length will be chosen as the most optimal one.
2. Delay: This is the measure of time it takes for the packet to route from source to destination. This depends on many factors like network bandwidth, the number of intermediate nodes, congestion at nodes, etc. Sooner the transfer, the better the Quality of Service (QoS).
3.  Hop count: This refers to the number of devices, usually routers, that a piece of data travels through
4. Bandwidth: This refers to the amount of data a link can transfer through it. Usually, the enterprise lease the network line to achieve a higher link and bandwidth.
5. Load: Load refers to the traffic which a router or a link is handling. The unbalanced or unhandled load might cause congestion and a lower rate of transmission packet losses.
6. Communication Cost: This is the operational expense which the company incurs by sending the packets on the leased line between the nodes.
7. Resilience and Reliability: This refers to the error handling capacity of the router and the routing algorithms. If some nodes in the network fail then the resilience and reliability measure will show us how well the other nodes can handle the traffic.

How does it take place?

When a packet is introduced in the network and received by one of the routers, it reads the headers of the packet to understand the destination and checks its routing table marked with it’s metrics to see what would be the next best hope for the packet to optimally reach the destination. Then, it pushes the packet to the next node and the above process repeats at the new node too until the packet reaches the destination node.

Types of Routing

Routing is classified into 3 categories, which are as follows:

• Static Routing
• Dynamic Routing
• Default Routing

1. Static Routing

Static routing is a method of routing that uses a manually configured routing table to define paths between routers. Static routes are fixed and do not change when the network is reconfigured or changed.

Advantages

• There is no CPU overhead for the routers to decide the next hop for the packet as the paths are predefined.
• This offers higher security as the administrator has autonomy over the permissions for packet flow along a defined path.
• Between the routers, no bandwidth would be used (for tasks like updating the it’s table, etc.)

Disadvantages

• For a larger network topology, it will be difficult for the administrator to identify and pre-define an optimal path from all possible combinations of source & destination nodes.
• The administrator would be expected to be thorough in the concepts of networks and topology. Transition to a new administrator would consume time so as understand the topology and policies that are defined.

2. Dynamic Routing

Dynamic routing provides router the ability to discover the network by protocols like OSPF (Open Shortest Path First) and RIP (Routing Information Protocol), updates the routing table by itself and effectively decides upon the path that the incoming packet must follow to reach its destination.

Advantages

• This is easy to configure.
• It would be efficient in order to discover some remote network and execute routing there.

Disadvantages

• When one of the routers in the network implementing dynamic routings discovers change or generates an update, it broadcasts it to all the nodes. Thus, consuming a higher amount of bandwidth.
• It is relatively less secure than static.

3. Default Routing

In default routing, the packets are forwarded without the specific address of the next hop. The default route is basically the address of another router. If the address on the packet matches the route, the packet is forwarded; else, it is forwarded through a default route of that router. The packet can be forwarded through any router which has been configured for default routing.

Advantages of Default Routing

• Default Routing can be used when there is no predefined route in the routing table.

Disadvantages of Default Routing

• The more complex the network is, the more difficult it is to set up and use efficiently.