Welcome to SolarWinds Blog Series ‘Basics of Routing Protocols’. This is the first of a four part series where you can learn more about the fundamentals of routing protocols, types and their everyday applications in network troubleshooting.


What is a Routing Protocol?

Routing protocols are used to determine the optimal path for data communication between nodes in a network. Routers use them to share routing information between other routers for building global routing tables dynamically.  Routing protocols are implemented when your network grows to the point where static routes are unmanageable.  Dynamic routing table management adjusts automatically for topology and traffic changes.

Routed Protocols on other hand contain the data required for a packet to be sent outside of its host network. They are the traffic that routers direct from source to destination. Examples are IP, HTTP, SSH, and SIP.


Different types of Routing Protocols

There are two major classes of routing protocols – Exterior Gateway Protocol (EGP) and Interior Gateway Protocol (IGP). EGP is a routing protocol used to exchange routing information between autonomous systems. For instance, EGP is used in data transfers between ISPs (Internet Service Providers) to ISPs or between autonomous systems to ISPs.

IGP (Interior Gateway Protocol) is used for exchanging routing information between routers within an autonomous system. For instance, IGP can be used in data transfer within your organization’s local area network. IGP can be further classified into two categories – Distance Vector and Link State Routing Protocols.


Distance-Vector vs. Link-State Routing Protocols

In Distance-Vector Routing Protocols, routers communicate with neighboring routers periodically informing them about network topology changes. Whereas in link-state routing protocol, routers create a roadmap of how they are connected in the network. By calculating the best path from that router to every possible destination in the network, link state routing protocols form the routing table.

RIP (Routing Information Protocol), RIPv2, IGRP (Interior Gateway Routing Protocol), EIGRP (Enhanced IGRP) are part of Distance-Vector Routing Protocols. OSPF (Open Shortest Path First), IS-IS (Intermediate System to Intermediate System) are part of Link-State Routing Protocols.


How to find the best routing protocol for your network?

Distance vector routing Protocols like RIP and EIGRP are ideal for small networks that are simple and non-hierarchical. Enterprises use link state routing protocols like OSPF and IS-IS for their large and hierarchical networks whilst distributed networks will use BGP to establish routing information between autonomous systems. For instance, network administrators using OSPF will have advanced knowledge about complex networks which helps them in troubleshooting routing related issues.

Additionally, network admins choose routing protocols based on convergence time, the time taken for all the routers to collect the status of current topological information about the network. If you have three routers in the network and one of the links that connects the network has failed, the information about the status should be immediately available in all the routers by the process of convergence. The slower they converge the harder they become for network admins to troubleshoot. Focusing on easing network route management, network configuration and troubleshooting are important when admins manage large enterprise networks


How can you monitor and troubleshoot route related network performance issues?

Advanced network monitoring tools have the ability to monitor network route information and provide real-time views on issues that might affect the network. Also, you can now view router topology, routing tables, changes in default routes, BGP transitions, and flapping routes.


You can learn more about popular routing protocols like RIP, OSPF and EIGRP in the blog series.