Routing Protocols: EIGRP vs OSPF

Routing protocols tell your routers how to talk to one another and then governs how each of these devices should distribute information. In short, it helps routers plan their routes and do their job well.

Businesses need to choose the right routing protocols for their network. It can spell the difference between being able to stream or have a reliable teleconference or not. The performance and speed enable you to work fast, getting the files you need to and from different places in the network or online.

It’s also important for a business network to remain accessible, because routing protocols are able to adjust to the changing conditions within the network, including the ability to detect which connections are offline and what obstructions exist.

There are several routing protocols available today, but two of the most often compared are Open Shortest Path First (OSPF) and Enhanced Interior Gateway Routing Protocol (EIGRP). Both are considered interior gateway protocols and work within a single routing domain.

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What is Open Shortest Path First (OSPF)?

Open Shortest Path First, commonly used in enterprise networks, uses shortest path first (SPF) technology to find and efficiently distribute routing information between routers on a local area network (LAN). Designed specifically for TCP/IP environments, OSPF routers are within the same network and will know about all the routers in that area. Those belonging to the same area will be able to pass along the information they’ve learned to adjacent routers, which are called neighbors.

 An OSPF system will be able to calculate the shortest path to a remote destination or router by using Dijkstra’s algorithm. This algorithm is used to find the shortest way between the source node to the destination node.

What is Enhanced Interior Gateway Routing Protocol (EIGRP)?

Designed  by Cisco Systems, Enhanced Interior Gateway Routing Protocol is a network protocol that allows your routers to trade information in a more efficient manner than similar protocols that came before it. EIGRP is fully interoperable with routers using the Interior Gateway Routing Protocol, from which it was based. It’s also used for Novell NetWare and AppleTalk networks.

 EIGRP routers keep a copy of the routing tables of their neighboring routers. When it needs to find a route, it scans these tables to find a suitable one. When it fails to find a route, the neighboring router will do it for them until a route is established.

EIGRP will determine the most efficient using a diffusing update algorithm, which is hosted on a finite state machine that will ultimately decide which is the least costly or most efficient route from the origin to the destination.

The Differences Between EIGRP and OSPF

EIGRP networks have routers that use both distance vector algorithm and link state. Distance vector algorithms dictate that routers should inform other routers of changes in its topology.  Each router will also have a table that lists down the distance between destination nodes and the router itself.

This protocol also requires the router to update itself when there are changes in the distance information of other routers, or if a link to another router is gone. So with a diffusing update algorithm doing the computation to find the shortest path, EIGRP networks have both the best path available and alternate paths.

Link state routing, on the other hand, doesn’t talk to all the routers in the area like an EIGRP router does. Instead, they exchange messages with another router to learn about the topology of the network. OSPF networks use the Dijkstra algorithm to find the shortest path.

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How EIGRP and OSPF Select the Shortest Path

EIGRP networks use a variety of metrics to select the route, including load, reliability, MTU, bandwidth, delay, and hop count. By default, these routers will consider delay and bandwidth.

EIGRP will be able to check out all the accessible paths from the source to the destination, and choose the shortest or the best path from the choices.

OSPF, on the other hand, uses cost to determine the path. It will choose the lowest cost path as the best one.

Other Differences

There are other differences that might influence which routing protocol to choose. First, there’s the administrative distance, with internal EIGRP being more reliable than OSPF. In turn OSPF have a smaller distance value than external EIGRP.

 What’s more, OSPF routing can take up a lot of your memory and CPU resources, significantly more than EIGRP. But the biggest consideration is that OSPF can be very complicated to implement, especially with larger networks.

OSPF vs. EIGRP: Which is Best for Your Business?

OSPF is much simpler to implement because it only considers the least cost. You should use OSPF for small networks. However, it may get complicated when the network gets larger. If you have a bigger site, you will want to make sure that you have the IT skills to keep things in line.

It works excellently for a variety of LAN and WAN environments. Or if you’re using devices and routers from different vendors. OSPF is open sourced and it’s easier to configure routers using this protocol. 

CISCO, on the other hand, claims that EIGRP is also an open standard, but they do not publish a lot of the core protocols in the RFC 7868 document that they prepared. Leaving out these details make it difficult for you to use another manufacturer’s router in an EIGRP network.

Enhanced Interior Gateway Routing Protocol is excellent for businesses that use CISCO routers. It’s less complex and provides fast convergence. It’s also a lot easier to configure.

 There is no way for one routing protocol to always be the best for your network or needs. It all depends on a lot of factors, like what IT skills you have, the amount of complexity you want, and how fast your business is growing. Both the EIGRP and OSPF have their merits and their drawbacks. It’s all a matter of what you prefer.

Read next: Creating a Network Audit Checklist

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