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What is EIGRP?

By Priya PedamkarPriya Pedamkar

What-is-EIGRP

Introduction to EIGRP

Enhanced Interior Gateway Routing Protocol or EIGRP automates the routing decisions and configurations in computer networking. Cisco designed the protocol and is available only on Cisco routers. Minimum bandwidth is used from the source to destination, and the delay is measured using metrics of the network. This is an advanced protocol to measure the distance and uses both link servicing and distance routing. Hence it is called a hybrid protocol. It transitions well with IPv6 and has the support of IPv4 as well. This is a classless routing technique. Two routers are connected, and the network is shared in EIGRP.

What is EIGRP?

Enhanced Interior Gateway Routing Protocol is an advanced distance vector routing protocol based on the principles of the Interior Gateway Routing Protocol (IGRP). It has a unique characteristic that improves the operational ability and fast converging rate. It can determine the shortest path distance vector, and it works on the principle of Interior Gateway Routing Protocol, a classless routing protocol. It uses metrics like bandwidth, load and delays to calculate the shortest optimal network route. It is a technologically, more advanced distance vector-based routing protocol. To exchange information using EIGRP, first and foremost, the routers need to become neighbors to EIGRP, then EIGRP uses the multicast address to share the information.

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Enhanced Interior Gateway Routing Protocol underlying logic is based on the concept of an autonomous system. In a system where each router should become neighbors to EIGRP and each system tagged as neighbors under Enhanced Interior, Gateway Routing Protocol will have the same system number configured.

Fundamentals of EIGRP

Enhanced Interior Gateway Routing Protocol (EIGRP) is a dynamic routing protocol used for routers’ decisions and configuration. EIGRP only sends incremental updates, which in short reduces the workload of the routers and the amount of information transmitted. EIGRP is a classic hybrid protocol that supports classless routing, it supports automatic & manual summarization on an EIGRP enabled interface. It MD5 authentication on routers running EIGRP and also has a maximum hop count close to 255. EIGRP performs load balancing over the equal-cost path and un-equal cost path.

To perform the functions of EIGRP, it creates three tables which are:

  • Neighbor Table
  • Topology Table
  • Routing Table

Following represents the ideology and concepts behind the three major tables:

1. Neighbor Table

  • The neighbor table contains information about routers and neighborship relationships with those whom have been established.
  • Command to list router information: ‘show ip eigrp neighbors’.
  • The Neighbor Table has Fields like H: Handle, Address, Interface, Hold Time, Uptime, Smooth Round Trip Time, Retransmission Timeout, Queue Count, Sequence Number.

2. Topology Table

  • The topology table holds information about all the paths to networks understood by EIGRP routers.
  • Command to list router information- ‘show ip eigrp’ topology.
  • The topology table holds the following fields Passive, Feasible Distance, Advertised distance, Feasible distance

3. Routing Table

  • The routing table stores the routes which are currently active in sending packets to the network. It stores the optimal route for the destination from the sender.
  • Command to List Router Information: ’show ipv6 route’.
  • The routing table holds the following fields D, 90/ 5632. Via 11.0.0.2, GigabitEthernet0/1.

Packet Types

  • Hello: It determines the neighbors’ router and also serves as a keep-alive mechanism between the routers. If Router X is connected with Router Y and the Router X is not receiving the hello packets from Router Y, then it assumes that Router Y is not reachable and the network is down.
  • Update: Updates are to send the information about the route to its neighbors. When a new router is found, the update packets sent to the neighbor to build up the topology table.
  • Query: Queries are used specifically for requesting route info. They act as multi-part until they send received queries as the response. It will send the queries only when the destination state is active.
  • Reply: Reply packets respond to a query that indicates the originator router that it does not need to go into an Active state as reliable successors for the destination network. Replies are sent when destinations go into an Active state. For the reply packet, an acknowledgment is sent.
  • ACK: Acknowledgment packet will be sent to Enhanced Interior Gateway Routing Protocol Query, Update and Reply packets. It is shared with unicast address and, also, acknowledgment not sent to Hello packets.

Benefits of EIGRP

  • Enhanced Interior Gateway Routing Protocol converges at fast rapid times for the changes in the network topology.
  • It makes use of link more effectively through (ECMP) Equal-Cost Multi-Path and unequal cost load sharing.
  • It performs a much easier transition with a multi-address family.
  • It supports both IPV4 and IPV6 networks.
  • It provides encryption for security and can be used with iBGP for WAN routing.
  • It reduces network traffic by making use of ‘need-based’ updates
  • Enhanced Interior Gateway Routing Protocol(EIGRP) is an advanced distance-vector routing protocol that is used on a computer network to help automate routing decisions and configuration.

Pros of EIGRP

  1. EIGRP with protocol-dependent modules can route several different layer protocols.
  2. EIGRP configuration was designed to be easy to configure.
  3. With EIGRP Autonomous number and network command, EIGRP can be enabled.
  4. EIGRP will converge in 200 milliseconds.
  5. EIGRP Is the protocol that performs unequal cost load balancing.
  6. If the destination has more than one link, it will identify the variance between the links.
  7. One of the more advanced features of EIGRP is Manual route summarization. It improves stability and reduces the routing table size.

Cons of EIGRP

  1. EIGRP routing protocol can be accessible with the CISCO network devices.
  2. EIGRP is a distance vector routing protocol, and it relies on routes provided by neighbors.
  3. It does not support future applications as it is not extensible.

Conclusion

EIGRP is the most advanced routing protocol that relies on distance vector, and state route links are effective in identifying the optimal route path. It will have more impact in real-time as it makes use of required resources, and the only disadvantage is that it is not extensible.

Recommended Article

This is a guide to What is EIGRP?. Here we discuss the Introduction to EIGRP and the Fundamentals, Benefits, Packet Types, and pros and cons. You can also go through our other suggested articles to learn more –

  1. Routing Algorithms
  2. Internet Control Message Protocol
  3. Types of Networking Protocols
  4. What is IPv4?
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