Classes of Routing Protocols

In this tutorial, we will discuss about the classes of the routing protocols.

Routing: What is it?

Routing in computer networks is a procedure in which the layer 3 or network layer devices carry out the operation of routing to send the packet by deciding on the best route from one network to another network.

There are three different routing types exist: they are

1. Static routing
2. Default routing
3. Dynamic routing

Static Routing

It is the first type of routing technique. This static routing can be defined as the process in which the routing database must be manually updated with new routes. That means the specific routes are added explicitly to the routing table.

The main benefit of this static routing process can be found as there is no specific routing overhead on the router CPU. This will allow for the usage of a less expensive router. And, because there will be only one administrator that permits routing to certain networks, it will increase the security. And the other important advantage is that in between the routers, there is no bandwidth utilisation.

Apart from the advantages, there are some drawbacks to this static routing, which is that an administrator must be well-versed in topology. A new administrator must manually add each route, so he or she must be intimately familiar with the topology's routes. This implies that the manual addition of each network route to the routing table on each router is a laborious operation for managers of big networks.

Default Routing

The second routing technique is called default routing. In this process, the router will be set up to deliver every packet to just one other router; that means the next hop. In this process, a router that just has one route to all other networks is known as a stub router. The major rule that is applied while processing this default route is that regardless of the network the packet is from, it will be routed to the router's default routing configuration. It is usually used in conjunction with stub routers.

Dynamic Routing

The third item on the list is dynamic routing, in which dynamic routing explains to us that, according to the current state of the route in the routing database, dynamic routing automatically modifies the routes. Dynamic routing protocols choose the optimum path from the available paths for the target network using metrics, cost, and hop count.

Protocols are used in dynamic routing to find network destinations and the paths to get there. The major protocol examples of dynamic routing are OSPF and RIPS. A router will notify all the other routers of a change in the topology when it discovers any changes in the topology. The important features of this route are that if you want to swap the routes, the routers need to be running on the same dynamic protocol.

The drawbacks of this route are that it uses more bandwidth while talking to nearby neighbours. But it is more secure when compared to the static routing process. And the main added advantage is that the configuration process is easy. That means it is simple to configure and it is more successful at detecting faraway networks as well as choosing the best path to get there.

Introduction to Classes of Routing

Depending on how they operate, routing protocols are categorised into the following three classes: they are

1. Distance vector routing protocol
2. Link state routing protocol
3. Advance distance vector routing protocol

Distance Vector Routing Protocol

This type of protocol will choose the optimum route based on the number of hops necessary to go in a specific direction to a target network. The example of this distance vector routing protocol is somewhat like the dynamic RIP protocol.

The number of routers between the source and destination networks is referred to as the hop count. The path that has the fewest hops will be determined to be the best one. The convergence of distance vector protocols takes more time to process. When every router on a network is aware of every destination network, this means that the network is said to be converged.

It is often easy and simpler to establish, maintain, and debug the Distance Vector protocols. However, because they send out the full routing table on a regular basis, even if there has been nothing changed between the periods, they require far more CPU and bandwidth.

They calculate the cost of a route using distance. The distance is determined by the number of hops between a router and the target network. The receiving router then incorporates the information based on AD and metrics into its routing table. As the receiving router trusts the information from the neighbour, this approach is known as "routing by hearsay."

Features of Distance Vector Routing Protocol

• Updates like route information are only exchanged with nearby nodes and they are not allowed to broadcast the updates.
• Only the distance vector is shared in updates rather than whole routing tables. Periodically, network updates are shared.
• Routing information that is obtained from nearby routers is always trusted by other routers. This is sometimes will be referred to as rumour route.

Drawbacks of Distance Vector Routing Protocol

• Like we discussed above, the routing information will be periodically exchanged, which results in the generation of unnecessary traffic that uses up available bandwidth. Additionally, network broadcasting periodically generates needless traffic.
• Because whole routing tables are communicated, there are security concerns. The entire architecture of the network will be relatively simple to comprehend if an unauthorised individual accesses it.

Link State Routing Protocol

Compared to other distance vector routing protocols, these protocols are more knowledgeable about the Internetwork. These also go by the acronym SPF, or Shortest Path First protocol. An example illustration of a link-state routing protocol is OSPF.

Three tables are maintained by the link state routing protocol, they are

1. Routing table
2. Neighbour table
3. Topology table

Routing table

In this table all the information about the best destination routes to the offered network is displayed

Topology table

All the topology information is available in this table. This table is also like routing table, but also the additional backup route’s information to the promoted network is available.

Neighbours table

In this table the contained information is about all the neighbours who have the adjacency relation.

Before exchanging the routing information, they will establish a neighbour relationship with other routers. These are opposed to distance vector protocols, which means they do not broadcast routing information to the whole network. They save the information about their neighbours on a table.

Unlike the distance vector protocols, which send out routing tables, they solely transmit data relating to connectivity or connection status. This information will be put on a topology table to generate a comprehensive image of the network. Each router will determine the optimum route to every destination in the network based on the connection states it has received. The optimum path is determined by an algorithm specific to each protocol.

And unlike the distance vector protocols, which provide link state updates on a regular basis, link state updates are only transmitted when there is a change required. Distance vector protocols converge more slowly than link-state protocols. Link-state protocols require a bit more configuration, management, and troubleshooting expertise. 

Features of Link State Routing Protocol

• Only the number of updates requested by the neighbouring router is shared.
• The idea of "triggered updates" is applied in other words, updates only happen when the topology changes.
• The neighbour detection and recovery process will use the hello messages for instance, sometimes these messages are referred to as keep-alive messages.

Benefits of Link State Routing Protocol

• As we discussed above it has a deeper understanding of the internetwork than any other distance vector routing protocol since it keeps distinct databases for the optimum route and the backup routes of the whole topology.
• When a topology changes, partial updates take place rather than a full update like in distance vector routing protocol, which involves exchanging the whole routing table.
• Since the concept of triggered updates is being implemented, there is no longer any irrational bandwidth usage, as there was with distance vector routing protocol.

Advanced Distance Vector Routing Protocol

The third one in the list is advance routing protocol of distance vector. The other name for this protocol is the hybrid routing protocol. This protocol is the implementation of both link state protocol and distance vector routing protocol respectively. The best example of an illustration of this protocol is EIGRP. The full form of EIGRP is Enhanced Interior Gateway Routing Protocol.

Due to its need for directly linked neighbours for route learning, EIGRP functions as a distance-vector routing protocol. EIGRP employs the Hello concept to find neighbours and establish an adjacency, acting as a link-state routing protocol. Partial updates are also started when a change happens.

Difference between Link State and Distance Vector Routing Protocols

The major differences between link state and distance vector routing protocols. They are

Distance Vector Routing Protocols

• The Bellman-Ford Algorithm is used to create routing tables.
• The bandwidth is not required. This is because of no flooding, sharing local and relatively small packets. At regular periods, neighbours share information with one another.
• In this dynamic routing system, each router calculates the distance to every potential destination, or its close neighbours.
• The router updates the table depending on its neighbours after sharing its knowledge of the whole network with its neighbours. Traffic and convergence are very much slow.
• Problem of the count to infinity that can be resolved by separating the horizon. In this example problem the points are
  Problem with persistent looping, in which the loop persists indefinitely.
  Good news spreads quickly, but negative news spreads more slowly.

• IGRP and RIP are implemented using distance vector routing protocol.

Link State Routing Protocol

• Routing tables are implemented using Dijkstra’s algorithm.
• A router uses flooding to relay information about its neighbours to all other routers. Converging and traffic is more in this protocol.
• It is a dynamic routing technique in which every router in the network provides information about its neighbours. Due to large packets and wide range of sharing there is more need for bandwidth.
• There is no use of count to infinity problem in this protocol.
• Using the TTL technique, means the time to live variable helps prevent flooding from leading to infinite looping.
• OSPF & ISIS are the example implementations.