Routing Protocols - Explained and Examples

A routing protocol discovers other routers and advertises the best pathway of communication between routers throughout the network, enabling any two nodes to communicate in a computer network. Protocols such as RIP, OSPF or EIGRP are the responsible for sharing information about their neighbors and the type of topology of the network.

There are many routing protocols and we are going to learn about 5 of the most popular routing protocols that make this process of communication be possible.

RIP

Routing Information Protocol (RIP) was developed in 1980s for routing messages and connecting small and medium size networks and handles up to 15 hops. Rip enabled routers to discover the network sending table routing requests from neighboring devices. Rip gets response containing full routing table from neighboring devices and adds them into its own table. With periodically updates for any changes across the network. RIP utilizes UTP ports 520,521 for its communication

OSPF

Open Shortest Path First (OSPF) is an Interior Gateway Protocol (IGP) and was developed to improve what was lacking in RIP including:

1. The 15 hop count limit.
2. The inability to organize networks into a routing hierarchy, the manageability and  the  performance on large internal networks.
3. The significant spikes of network traffic generated by repeatedly re-sending  full router tables at scheduled intervals.

OSPF is a link-state protocol, uses metric of cost, which is based on a link speed between two routers became popular for its scalability, fast convergence and vendor interoperability. Supports Internet Protocol Version 4 (IPV4) and supports Internet Protocol Version 6 (IPV6) networks and Classless Inter-domain Routing (CIDR).

EIGRP & IGRP

Enhanced Interior Gateway Routing Protocol (EIGRP)  is a distance vector-based routing protocol, using the Algorithm Diffused Update Algorithm (DUAL) to calculate the shortest path to a destination. It is similar to the Interior Gateway Routing Protocol (IGRP) in calculating the metric, but has many enhancements such as fast convergence, incremental updates, and support for multiple layers of IP, Internetwork Packet Exchange (IPX) and AppleTalk protocols. It is also worth mentioning that EIGRP is Cisco proprietary, so its implementation is restricted to cisco devices.

IS-IS

Intermediate System to Intermediate System (IS-IS) is a Link-state protocol and similar to OSPF. It uses a configurable, yet dimensionless, metric associated with an interface and runs Dijkstra’s shortest Path first algorithm. Although IS-IS as an IGP offers the scalability, fast convergence, and vendor- interoperability benefits of OSFP.

BGP & EGP

The Border Gateway Protocol (BGP) is considered to be the protocol that runs the internet which is an interconnection of multiple autonomous systems and referred as External Gateway Protocol (EGP). BGP detects modifications to routing tables and selectively communicates those changes to other routers over TCP/IP.
Internet providers commonly use BGP to join their networks together. Additionally, larger business sometimes also use BGP to join together multiple of their internal networks. Professionals consider BGP the most challenging of all routing protocols to master due to its configuration complexity.