What is EIGRP? | The Enhanced Interior Gateway Routing Protocol in Networking

If you work with computer networks, you might have heard about something called the Cisco EIGRP protocol. But it would be best if you found out what it really is and what it does. So, EIGRP stands for Enhanced Interior Gateway Routing Protocol.

In simple terms, EIGRP does its job by exchanging information about the best paths within an autonomous system (AS). Also, it’s a way for Cisco devices to talk to each other.

What is EIGRP Protocol?

What Exactly is EIGRP and What Does It Do?

They made the EIGRP protocol to create networks that are easy to grow, work well, and don’t have problems. Think of it like a newer and better version of IGRP (Interior Gateway Routing Protocol).

Since it is a more advanced version of the IGRP protocol, it calculates the best path to the target network. While doing this, it uses a more complex algorithm.

This protocol is a mix of Distance Vector and Link State routing. In simple terms, it acts as a Hybrid protocol. Further, they made it better because the old RIP distance vector had some problems.

It also provides Classless VLSM support. Thus, it uses the Autonomous System numbering system. In this way, it creates a router group that uses the same routing protocol.

This unique Cisco protocol uses something called “distance” to pick the best way to go. Distance here means things like how fast, how reliable, and how busy a connection is. EIGRP looks at all these things to figure out the best route. Because of this, it can guide traffic more smartly compared to other routing methods.

What is EIGRP’s History and Development?

They developed the EIGRP protocol to help routers share information on PC networks. When we look at its history, it dates back to the 1980s.

Back in the day, Cisco made a way for routers in IP networks to share information about routing tables.

After a while, in 1994, Cisco swapped out IGRP for EIGRP. They did this to fix the issues seen in other protocols like RIP and OSPF. So, they developed these protocols to be faster and more efficient. They also enabled the devices to adjust to changes in the LAN quickly.

As time passed, it has gone through many revisions and improvements. Then, in 1996, a group called the IETF (Internet Engineering Task Force) made it a standard. Now, other companies are also using this protocol in their devices.

In 1998, they introduced something called DUAL (Diffusing Update Algorithm). This improvement made devices talk to each other faster. So they could quickly figure out the best route for data traffic.

The DUAL algorithm maintains a backup route for each route. If the primary path fails, it tells the Routers to go to the backup path quickly.

Cisco introduced a more updated version, EIGRPv6, designed for IPv6 networks in 2004. This version includes new metrics for IPv6 support and path selection.

What are the EIGRP Protocol Features?

Here are some features of this protocol that make it a popular choice:

  1. Fast Convergence

It helps the network bounce back fast after a problem. It uses DUAL to figure out alternative routes to reach the destination. This way, routers can talk to each other quickly if there’s a connection issue.

  1. Reliability

It makes things more reliable by spreading the workload and having backup plans. It shares traffic across different paths to the same place, making the LAN work better and avoiding traffic jams. Plus, it keeps backup routes to the destination, adding another layer of reliability.

  1. Scalability

It is excellent for extensive LANs with lots of routers. It can handle a large scale of operations, making things highly scalable. In short, it allows you to split your LAN into smaller Autonomous Systems (AS). Ultimately, you reduce routing size and increase network performance.

  1. Bandwidth

It uses a mix of measurements to figure out the best way to reach a network. This metric value is bandwidth efficient. That is, it calculates the bandwidth, latency, reliability, and load of the LAN. Then, it sends traffic through the quickest and most efficient route.

  1. Security

Lastly, it comes with safety features to keep the network safe from unauthorized access and attacks. It only shares routing details with only to authorized devices. In this situation, it uses something called MD5 authentication for extra security. Also, it supports route summarization for external LANs.

How Does the EIGRP Protocol Work?

It uses a hierarchical topology layout. That is, it follows a design with different levels, like branches on a tree. The central part, called the backbone or core, is right in the middle of the network. Thus, it connects all branch areas. In short, branches connect to the backbone with ABRs (Area Border Routers).

These metrics include to check the best path to a LAN:

  • Bandwidth: This means how much info travels through a connection in a set amount of time.
  • Delay: The time it takes for a packet to transit from one end of the link to the other.
  • Reliability: This shows if a connection might have trouble or if some data might not make it through.
  • Load: It refers to the amount of traffic on a connection.

Also, EIGRP uses composite metrics to figure out the best route. In short, this is like a formula made by putting together the values we talked about earlier.

The formula for the EIGRP protocol composite metric is as follows:

metric = (K1 bandwidth) + + (K3 delay) + (K4 delay * reliability)

  • K1, K2, K3, and K4 are values configurable by the network administrator.
  • Bandwidth is how fast the network connection is, measured in kilobits per second.
  • Load is the load of the connection in percent.
  • Delay is the total delay of the path in microseconds.
  • Reliability is a number between 0 and 255 that tells us how dependable the connection is.

What is the Table of Enhanced Interior Gateway Routing Protocol?

EIGRP protocol, unlike RIP, has two ways of looking at the LAN. These are:

  1. Neighbor Table

The neighbor table gives details about the networks directly linked to the Router. It includes info like IP addresses, the kind of interface, or how much data it can handle (bandwidth).

  1. Topology Table

The topology table is like a map of the network, showing all the routes from nearby routers.

As a result of a change in a LAN, the Topology table comes into play. It uses this table to find the best alternative path. If there is no route here, it queries neighboring Routers.

Besides, it uses two Distance Values. It uses the 90 metrics for routes it has learned itself. Yet, it uses the 170 metrics for routes learned by other protocols.

Watch our YouTube videos to learn about EIGRP!

Video 1

Video 2

Frequently Asked Questions About EIGRP (FAQ)

  1. What is the simple definition of EIGRP?
It’s the best way to send data in a network. Think of it as a newer version made by Cisco to improve on IGRP. Its primary function is to reduce congestion and increase LAN performance.
  1. How does EIGRP work?
Determines the best path for IP packets to travel within a network. But, in doing so, it, of course, uses bandwidth and a latency-based metric. Then, when a Router on the LAN receives a data packet, it examines the destination address. It then uses the EIGRP metric to determine the best path to send the data. Finally, the Router then sends the data along this path.
  1. Can I use it with other routing protocols?
Yes, you can use EIGRP with other routing protocols. In fact, it is often used with others as it increases redundancy and performance. In short, its use is familiar with protocols such as OSPF and BGP.
  1. Is EIGRP secure?
This protocol from Cisco is definitely safe. It has a security feature called MD5 authentication, making sure data goes only to approved devices. Plus, it supports different security methods like both MD5 and simple password authentication.


As a result, EIGRP offers a hybrid approach to routing. Thus, it is an advanced and reliable routing protocol. That is, it determines the best path to the target device on the network. In this case, it uses a combination of distance vector and link state methods.

EIGRP supports the LAN being always loop-free. So, it uses an intelligent algorithm called DUAL to find the best way. In short, it can use different paths to get to the destination. Thus, it’s good at spreading the workload evenly.

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