Updated June 22, 2023
Introduction to EIGRP
Enhanced Interior Gateway Routing Protocol or EIGRP automates the routing decisions and configurations in computer networking. Cisco designed the protocol, and it is available only on Cisco routers. Minimum bandwidth is used from the source to the destination, and the delay is measured using network metrics. This advanced protocol measures 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 connect, and they share the network using EIGRP.
What is EIGRP?
Enhanced Interior Gateway Routing Protocol is an advanced distance vector routing protocol based on the principles of Interior Gateway Routing Protocol (IGRP). It has a unique characteristic that improves operational ability and fast converging rate. It can determine the shortest path distance vector and works on the Interior Gateway Routing Protocol principle, a classless routing protocol. It calculates the shortest optimal network route using bandwidth, load, and delays metrics. 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.
Enhanced Interior Gateway Routing Protocol’s 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 for routers’ decisions and configuration. EIGRP only sends incremental updates, reducing the routers’ workload 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 has MD5 authentication on routers running EIGRP and a maximum hop count of 255. EIGRP performs load balancing over the equal-cost path and unequal-cost path.
To perform the functions of EIGRP, it creates three tables which are:
- Neighbor Table
- Topology Table
- Routing Table
The 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 who 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, and Sequence Number.
2. Topology Table
- The topology table contains information about all the paths to networks EIGRP routers understand.
- 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 active routes 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 188.8.131.52, GigabitEthernet0/1.
- Hello: It determines the neighbors’ router and is a keep-alive mechanism between the routers. If Router X is connected with Router Y and Router X is not receiving the hello packets from Router Y, then it assumes that Router Y is unreachable and the network is down.
- Update: Updates are to send the information about the route to its neighbors. When a new router is discovered, the neighbor receives update packets to establish and populate the topology table.
- Query: Users explicitly use queries to request route information. 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 does not need to go into an Active state as a reliable successor for the destination network. Destinations send replies when they 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 a unicast address, and acknowledgment is not sent to Hello packets.
- Enhanced Interior Gateway Routing Protocol converges at fast rapid times for the changes in the network topology.
- It uses links 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 users can utilize it 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 used on a computer network to help automate routing decisions and configuration.
Pros and Cons of EIGRP
Given below are the pros and cons:
- EIGRP with protocol-dependent modules can route several different layer protocols.
- The designers intended to create EIGRP configuration to be easy to configure.
- With EIGRP Autonomous number and network command, EIGRP can be enabled.
- It will converge in 200 milliseconds.
- It is the protocol that performs unequal cost load balancing.
- If the destination has more than one link, it will identify the variance between the links.
- One of the more advanced features of EIGRP is Manual route summarization. It improves stability and reduces the routing table size.
- EIGRP routing protocol can be accessible with the CISCO network devices.
- It is a distance vector routing protocol that relies on neighbors’ routes.
- It does not support future applications as it is not extensible.
EIGRP is the most advanced routing protocol that relies on distance vectors and state route links effectively identify the optimal route path. It will have more impact in real-time as it uses the required resources, and the only disadvantage is that it is not extensible.
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