Routing Protocols Overview

There are different techniques and methods for maintaining accurate routing information, thus different types of routing protocols were invented over the years.

The following post is intended to offer you an overview of the different types of routing protocols currently available.

Distance Vector / Link State

The above terms refer to the algorithms that govern the exchange of routing information and the way the optimal path is identified.

Distance vector protocols exchange information previously incorporated in the device’s routing table. The routers know only their immediate neighbor (one hop away). The link-state algorithms on the other hand, exchange information regarding the status of the links in the whole network topology (they have a bigger picture of the network).

Distance vector protocols require less hardware resources, but are sensitive to the formation of routing loops. Link state protocols require more hardware resources but are more efficient and converge better.

The following are distance vector protocols: RIPv1, RIPv2, IGRP, EIGRP.
The following are link-state protocols: OSPF, IS-IS.

Classless / classful.

Classful protocols publish only the address information of the destination network, not the subnet mask, which forces the device receiving the update to assume that the subnet mask is the same as that on its interface, or the default mask that corresponds to the class.

Classless routing protocols however, advertise the subnet mask together with the network address, so the receiving router has full routing information. This allows the implementation of VLSM and CIDR.

Classful protocols: RIPv1, IGRP.
Classless Protocols: RIPv2, EIGRP, OSPF, IS-IS.

Internal Routing Protocols / External Routing Protocols.
The interior routing protocols (or IGP – Interior Gateway Protocols) are designed to operate within the same administrative domain, which means that each device is “confident” about the information received from others.

Exterior routing protocols (or EGP such as BGP), however, are used to manage routing between different administrative domains. In EGP, each administrative domain is independent. It has implemented its own routing policy.

Interior routing protocols: RIPv1, RIPv2, EIGRP, OSPF, IS-IS.
Exterior Routing Protocol: BGPv4.