Routing Protocols in Practice: OSPF, BGP & EIGRP

Introduction

"Knowing how routing works is theory. Knowing which protocol to run is engineering."

Routers can learn paths in different ways, but real networks rarely use just one method. A company campus, an internet provider, and a multi-cloud platform each have different needs, so each uses different tools.

Three protocols appear again and again: OSPF, EIGRP, and BGP. The first two usually work inside a single organization's network, while BGP connects networks to each other. Let's see what each does and where it fits.

1. OSPF: The Interior Standard

"Inside your own network, everyone should share the same map."

OSPF (Open Shortest Path First) is a link-state protocol and an interior gateway protocol (IGP), meaning it routes traffic within one organization's network, known as an autonomous system.

Each OSPF router describes its directly connected links and floods that information to the others in its area. Every router then builds the same topology map and runs Dijkstra's algorithm to find the lowest-cost path. Cost is typically based on link bandwidth, so faster links are preferred.

To stay manageable in large networks, OSPF divides them into areas. All areas connect to a central backbone, Area 0, which keeps routing updates local and reduces the load on each router.

Because OSPF is an open standard, it works across equipment from different vendors. That makes it a common choice for enterprise campuses, data centres, and service provider cores.

2. EIGRP: Fast and Simple, Mostly Cisco

"Not every network needs the heaviest tool. Some need the quickest one."

EIGRP (Enhanced Interior Gateway Routing Protocol) is another interior protocol. It began as a Cisco technology and is often described as an advanced distance-vector or hybrid protocol.

Like distance-vector protocols, EIGRP learns routes from neighbours. Unlike simple ones such as RIP, it uses a smarter algorithm called DUAL, which calculates a primary route and keeps loop-free backups ready. If the main path fails, the router can switch to a backup almost instantly instead of recalculating from scratch.

EIGRP's metric combines bandwidth and delay by default, and it is known for easy configuration and fast convergence. Cisco published part of the protocol as an open specification in 2016, but it remains most common in Cisco-based enterprise networks.

3. BGP: The Protocol That Runs the Internet

"The internet is not one network. It is thousands of networks agreeing to talk."

BGP (Border Gateway Protocol) is an exterior gateway protocol. Instead of finding the shortest path inside one network, it exchanges routes between autonomous systems, each identified by an AS number. Internet providers, large companies, universities, and cloud platforms all use BGP to announce which IP ranges they can reach.

BGP is a path-vector protocol. Each route carries the list of autonomous systems it has passed through, called the AS path. This tells a router how a destination is reached and helps prevent loops, because a router rejects any route that already contains its own AS number.

BGP also dominates multi-cloud and hybrid connectivity. Dedicated links to cloud providers, such as AWS Direct Connect, Azure ExpressRoute, and Google Cloud Interconnect, commonly use BGP to exchange routes between an on-premises network and the cloud. The same applies when linking one cloud to another.

4. When to Use Each, and Why BGP Is Prized

"The best protocol is the one that matches the problem."

A simple rule of thumb:

• OSPF: Vendor-neutral routing inside an enterprise or provider network.
• EIGRP: Fast, easy routing inside a mostly Cisco environment.
• BGP: Connecting separate networks, such as ISPs, cloud providers, or multiple sites needing policy control.

Many networks run more than one. A company might use OSPF internally and BGP at the edge to reach its providers.

BGP is prized for three reasons:

• Scale: It handles the global internet routing table, which holds over a million routes.
• Policy control: Operators can prefer certain paths, influence incoming traffic, or limit which routes they accept, based on business and cost decisions rather than just speed.
• Stability: It changes cautiously and shields networks from each other's internal changes.

The trade-offs are slower convergence and greater risk. A misconfigured BGP announcement can send traffic to the wrong place, so careful filtering matters.

Conclusion

"Routing protocols do not compete as much as they divide the work."

OSPF gives enterprises a shared, vendor-neutral map, EIGRP offers quick and simple routing in Cisco-centred networks, and BGP connects independent networks across the internet and the cloud. Choosing well means asking where the network sits and how much control it needs.

In the next article, we'll explore the Transport Layer and its two main protocols, TCP and UDP, which help applications communicate across networks.