Centralised Routing vs Distributed Routing Protocols
Routing is the process of choosing which paths to be used to send network traffic, and sending the packets along the selected sub network. In computer networking terminology, a routing protocol defines how nodes in networks (specifically routers) interact with each other, to decide which paths to choose for sending network traffic by sharing necessary link information. Typically, the nodes have initial knowledge of other nodes connected to it directly and the routing protocol will spread this information first to the nearby nodes and then to the other nodes. This is how routing protocols provide knowledge of network topology to the routers of the network initially as well as after a change has occurred.
There are two types of routing protocols classified as dynamic and static protocols. Static protocols only work with manually configured routing tables, while dynamic protocols adaptively update routing table(s) according to changes in network topology. Dynamic protocols are further classified as centralized and distributed. Centralized protocols focus on a central node for all routing decision, while distributed protocols make each device in the network responsible for making routing decisions.
What are Centralised Routing Protocols?
As mentioned above, centralized routing protocols belong to the family of dynamic routing protocols. In a network that uses a centralized routing protocol, a central processing device running on a “central” node gathers information (status such as up/down status, capacity and current utilization) on each link in the network. Then, this processing device uses the gathered information to compute routing tables for all other nodes. These routing protocols make use of a centralized database located at the central node for these computations. In other words, the routing table is kept at a single “central” node, which should be consulted when other nodes need to make a routing decision.
What are Distributed Routing Protocols?
Distributed routing protocols also belong to the family of dynamic routing protocols. Under distributed routing protocol, each device in the network is responsible for making routing decisions. There are two types of dynamic, distributed protocols called isolated (nodes do not communicate) and non-isolated (nodes communicate with each other). So, under this sub category (dynamic, distributed and non-isolated), there are two broad classes of protocols that are used more commonly today. They are distance vector protocols and link state protocols. Distance vector protocols make the nodes share information such as destination and cost at regular intervals or as-needed basis. Link state protocols floods the link state information throughout the network to allow each node to build a network “map”.
What is the difference between Centralised Routing Protocols and Distributed Routing Protocols?
Although both centralized and distributed routing protocols are dynamic routing protocols, they are quite different in how they operate. The main difference between them is based on which devices in the network are making the decisions regarding routing. One central node is responsible for all routing decisions in centralized routing, while each device is responsible for routing decisions under distributed protocols. Centralized protocols have many problems compared to distributed protocols, such as having a single point of failure and potential network congestion around the central node. Because of these reasons, distributed protocols are more commonly used.