Uncovering the mechanism of routing protocols that automatically determine the optimal route

First, let's take a look at the routing protocols that are typically used in corporate networks. The topic to be discussed is RIP (Routing Information Protocol). Its simple structure makes it suitable for learning purposes.

First, let's check the types and characteristics of routing protocols. Currently, the routing protocols that are mainly used can be roughly divided into four types: "distance vector type", "link state type", "advanced distance vector type", and "path vector type".

As you can see from the fact that the distance vector type contains the word "distance", routers exchange distance information to the destination network and determine the route. It is a protocol that chooses the The oldest of the four types. It is said that the RIP, one of the distance vector types, was prototyped in the 1960s. The first RFC 1058, which defines the specification, was created in 1988.

The feature of the distance vector type protocol is that the load on the router is low because the mechanism is simple. Neighboring routers exchange simple information, such as the number of routers to pass through to the destination and link information connecting to the destination, to determine the route.

On the other hand, it has the disadvantage of not being suitable for large-scale networks. This is because when there is a change in routing information, adjacent routers exchange routing information, so it takes time for the settings to be reflected in all routers. For example, even if a failure occurs and a route change is necessary, it is not immediately reflected in the routing table.

In addition, since broadcasting is used to exchange route information, there is also the problem of unnecessary traffic when the number of routers increases.

The link-state protocol was developed to be suitable for large-scale networks rather than the distance vector protocol.

The feature is that each router determines the optimal route information after grasping the link information (information on the interface to connect) of other routers. Even if the network configuration changes due to a failure, each router understands the entire network, so the route can be switched faster than the distance vector type. However, the load on each router is higher than the distance vector type.

The advanced distance vector type combines the strengths of the distance vector type and the link state type. "EIGRP (Enhanced Interior Gateway Protocol)" is an evolution of the "IGRP (Interior Gateway Routing Protocol)" protocol independently developed by US Cisco Systems.

It has both the feature of the distance vector type that the mechanism is simple and the feature of the link state type that the route change is reflected quickly.

A path vector protocol was conceived for larger networks than the link state protocol. Mainly used for Internet-wide routing. "BGP (Border Gateway Protocol)" corresponds to the path vector type.

In order to be able to handle a large number of routes, the feature is that it adopts a mechanism to determine routes by simply exchanging information. Since it is responsible for routing for the entire Internet, it reduces the load on each router.

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