Key differences between Enhanced Interior Gateway Routing Protocol (EIGRP) and Interior Gateway Routing Protocol (IGRP)

Enhanced Interior Gateway Routing Protocol (EIGRP)

Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance-vector routing protocol developed by Cisco Systems. It is designed for fast, efficient network routing within an autonomous system. EIGRP optimizes the routing process by dynamically updating router tables only when changes occur, reducing bandwidth usage and enabling rapid convergence. It combines the best features of link-state and distance-vector protocols, such as the use of metrics (including bandwidth, delay, load, and reliability) for selecting optimal paths, and supports classless inter-domain routing (CIDR), allowing for efficient use of IP addresses. EIGRP’s use of Diffusing Update Algorithm (DUAL) ensures loop-free routes and quick recalculation of routes if a network topology changes, making it a reliable and scalable choice for enterprise network routing.

Functions of EIGRP:

• Rapid Convergence:

EIGRP quickly adapts to network changes, recalculating routes and converging rapidly when links go down or when alternative paths become available, minimizing downtime.

• Efficient Use of Bandwidth:

It uses a partial update mechanism, where updates are sent only when there is a change in the topology that affects the routing information. This reduces the bandwidth used for routing information.

• Load Balancing:

EIGRP supports equal and unequal cost load balancing, allowing traffic to be distributed across multiple paths to optimize network bandwidth and reduce congestion.

• Route Summarization:

It allows for manual and automatic route summarization, reducing the size of the routing table and improving network scalability and efficiency.

• Protocol-Independent:

EIGRP is protocol-independent, supporting multiple network layer protocols like IP, IPv6, and IPX, through the use of protocol-dependent modules.

• Scalability:

It is designed to scale well in both small and large networks, thanks to its efficient use of bandwidth and ability to summarize routes.

• Metric Calculation:

EIGRP uses a composite metric based on bandwidth, delay, load, and reliability to determine the best path to a destination, providing a more accurate and flexible method for route selection compared to traditional distance-vector protocols.

• Neighbor Discovery and Recovery:

EIGRP uses Hello packets to discover and maintain neighbor relationships on directly connected networks. This ensures that routers know about each other and can exchange routing information.

• Stable Routing Environment:

It implements the DUAL (Diffusing Update Algorithm) to ensure loop-free and reliable routing, maintaining a stable routing environment even in the face of network changes.

Components of EIGRP:

• Neighbor Table:

This contains a list of all neighboring routers with which direct communication has been established. The neighbor table is built using Hello packets to discover neighbors and maintain adjacency.

• Topology Table:

Also known as the EIGRP topology database, this table stores all the routes learned from EIGRP neighbors. It includes not only the best routes but also backup routes (feasible successors) that can be used if the primary route fails.

• Routing Table:

Selected best paths from the topology table are placed into the routing table. These routes are used for forwarding packets towards their destination. Only the best route to each destination, as determined by EIGRP’s composite metric, is included in the routing table.

• Protocol–Dependent Modules:

EIGRP can route different network layer protocols such as IP, IPv6, and IPX. For each routed protocol, EIGRP maintains separate neighbor tables, topology tables, and routing tables.

• Diffusing Update Algorithm (DUAL):

DUAL is the algorithm used by EIGRP to ensure loop-free and reliable routing. It is responsible for calculating the shortest path and a feasible successor as a backup route. DUAL allows for rapid convergence and minimizes the bandwidth used for routing updates.

• Hello and Acknowledgment Packets:

These are used for neighbor discovery and to maintain neighbor relationships. Hello packets are sent periodically to discover new neighbors and check the status of existing ones. Acknowledgment packets are used to acknowledge the receipt of EIGRP packets.

• Update, Query, and Reply Packets:

Update packets are used to propagate routing information changes. Query packets are sent when a router needs information about a route, and Reply packets are sent in response to Query packets.

• Composite Metric:

EIGRP uses a composite metric that considers bandwidth, delay, load, and reliability to select the best path to a destination. This metric is customizable, allowing network administrators to influence route selection based on their specific network requirements.

Advantages of EIGRP:

• Fast Convergence:

EIGRP features quick convergence times following network changes, thanks to its use of the Diffusing Update Algorithm (DUAL). This ensures minimal downtime and disruption to network services.

• Efficient Bandwidth Use:

It minimizes the use of network bandwidth by sending partial updates only when there is a change in the network topology, as opposed to periodic full-table updates.

• Scalability:

EIGRP can scale to large networks due to its efficient use of bandwidth and ability to summarize routes, reducing the size of routing tables.

• Load Balancing:

EIGRP supports both equal and unequal cost load balancing, allowing traffic to be distributed across multiple routes to optimize network performance and resource utilization.

• Flexible Metric System:

The composite metric used by EIGRP takes into account bandwidth, delay, load, and reliability, providing the ability to fine-tune route selection according to the network’s needs.

• Support for Multiple Network Layer Protocols:

EIGRP is designed to be protocol-independent, with support for IP, IPv6, and IPX. This makes it versatile for routing different types of network protocols.

• Automatic Route Summarization:

EIGRP can automatically summarize routes at network boundaries, improving efficiency and reducing the size of the routing table.

• Robust Network Topology Management:

The protocol maintains a topology table that stores all learned routes, including backup routes, which can be quickly utilized in case of a primary route failure.

• Easy Configuration and Maintenance:

Compared to some other routing protocols, EIGRP is relatively straightforward to configure and maintain, with fewer parameters that need to be manually set.

• Network Stability:

DUAL ensures that EIGRP maintains a loop-free and stable routing environment, even in complex network topologies and during network transitions.

• Compatibility and Interoperability:

For networks that have used Cisco’s IGRP, EIGRP provides an easy upgrade path with backward compatibility features, facilitating smooth transitions.

Disadvantages of EIGRP:

• Cisco Proprietary:

Originally EIGRP was a Cisco proprietary protocol, which limited its use to Cisco devices. Although Cisco has since released basic information about the protocol for standardization, its fullest implementation and advanced features might still be best supported on Cisco equipment, potentially leading to vendor lock-in.

• Complexity:

Despite its efficiency and fast convergence, EIGRP’s algorithm (DUAL) and the overall protocol can be complex to fully understand and optimize, especially in very large and complicated network topologies.

• Resource Intensive:

EIGRP can be more CPU and memory-intensive than simpler routing protocols due to its advanced calculations and maintenance of multiple tables (neighbor, topology, and routing tables). This might be a consideration for networks running on older or less powerful hardware.

• Limited External Protocol Support:

While EIGRP supports multiple network layer protocols, its fullest capabilities and most advanced features are primarily designed around IP routing. Networks heavily utilizing other protocols might not benefit as much from EIGRP’s features.

• Partial Updates Can Still Lead to Bandwidth issues:

In very large and dynamic networks, the frequency of partial updates due to topology changes can still consume significant bandwidth and processing resources, impacting network performance.

• Interoperability Challenges:

While EIGRP can work in a multi-vendor environment through the use of EIGRP stub routing or redistribution into other routing protocols, these setups can increase complexity and might not offer the same level of performance and features as in a homogeneous Cisco environment.

• Manual Tuning for Optimal Performance:

To fully leverage EIGRP’s capabilities, especially in complex scenarios, requires manual tuning of metrics and timers. This can increase the administrative overhead and requires a deeper understanding of the network and the protocol.

• Route Summarization and Aggregation:

While automatic route summarization is often seen as an advantage, if not carefully planned, it can lead to suboptimal routing decisions and inconsistencies in the routing table, requiring manual adjustments.                                                       

Interior Gateway Routing Protocol (IGRP)

Interior Gateway Routing Protocol (IGRP) is a distance-vector routing protocol developed by Cisco Systems in the mid-1980s, designed to overcome the limitations of earlier routing protocols like RIP (Routing Information Protocol). IGRP was created to support larger and more complex networks, with an emphasis on providing greater network flexibility and reducing overhead. It achieves this by utilizing a composite metric that considers multiple factors, including bandwidth, delay, load, and reliability, to determine the best path for data packets. This allows for more nuanced and efficient routing decisions compared to protocols that rely on a single metric, such as hop count. IGRP also introduced features like route poisoning and triggered updates to improve routing stability and convergence times. However, it was eventually superseded by Enhanced Interior Gateway Routing Protocol (EIGRP), which offered further improvements in terms of scalability, convergence, and network resource utilization. Despite its retirement, IGRP laid important groundwork for modern routing protocols, emphasizing the need for adaptability and efficiency in network routing.

Functions of IGRP:

• Routing Information Exchange:

IGRP facilitates the exchange of routing information between routers within an autonomous system. This enables routers to build a comprehensive picture of network topology and available routes.

• Route Selection:

Utilizing a composite metric that combines bandwidth, delay, reliability, load, and Maximum Transmission Unit (MTU) size, IGRP selects the most efficient route for data packets. This composite metric allows for more nuanced and efficient route determination compared to simpler metrics used by other protocols.

• Load Balancing:

IGRP supports unequal cost load balancing, which allows it to distribute traffic across multiple routes with different metrics. This capability optimizes bandwidth usage and enhances network performance.

• Automatic Route Updates:

IGRP automatically updates routing tables at regular intervals and in response to network changes. This ensures that routers have up-to-date information about network topology and available routes.

• Avoidance of Routing Loops:

Through the use of algorithms such as Split Horizon, Route Poisoning, and Hold-Down timers, IGRP minimizes the occurrence of routing loops, enhancing network stability and reliability.

Components of IGRP:

• Routing Table:

This is a database where IGRP stores information about known routes to various network destinations. The routing table includes metrics associated with each route, which IGRP uses to select the best path for packet forwarding.

• Update Mechanism:

IGRP employs a periodic update mechanism to exchange routing information between routers. Every 90 seconds (by default), routers broadcast or multicast their entire routing table to their immediate neighbors, ensuring that the network’s routing information is up-to-date.

• Composite Metric:

IGRP uses a composite metric that combines several factors—bandwidth, delay, load, reliability, and Maximum Transmission Unit (MTU) size—to evaluate the best path for data transmission. This allows IGRP to make more sophisticated routing decisions than protocols that rely on a single metric like hop count.

• Algorithm:

The Diffusing Update Algorithm (DUAL) is employed by IGRP’s successor, EIGRP, but IGRP itself uses a distance-vector algorithm to determine the shortest path to each network destination. The algorithm calculates the best route based on the composite metric of each path.

• Timers:

IGRP utilizes several timers to manage its operations, including update timers (for the periodic sending of routing information), invalid timers (to mark a route as invalid if not updated within a certain timeframe), holddown timers (to prevent route flapping and ensure network stability), and flush timers (to remove invalid routes from the routing table).

• Network Layer Protocol Support:

While primarily designed for IP networks, IGRP can route multiple network layer protocols, making it versatile in multi-protocol environments.

• Split Horizon and Route Poisoning:

These mechanisms help prevent routing loops by controlling the propagation of routing information. Split Horizon prevents a router from advertising a route back on the interface from which it was learned, and Route Poisoning marks failed routes with an infinite metric to inform other routers of their inaccessibility.

Advantages of IGRP:

• Support for Large Networks:

IGRP supported larger network environments than RIP by allowing for a higher maximum hop count. RIP was limited to a maximum of 15 hops, whereas IGRP extended this to support networks with up to 255 hops, facilitating routing in larger and more complex topologies.

• Composite Metric:

Unlike RIP, which uses hop count as its sole metric, IGRP introduced a composite metric that considered bandwidth, delay, load, and reliability to select the best path. This allowed for more nuanced and efficient routing decisions, as routes were chosen based on actual network performance rather than just the number of hops.

• Load Balancing:

IGRP was capable of performing unequal cost load balancing, distributing network traffic across multiple paths with different metrics. This was a significant improvement over protocols that only supported equal cost load balancing, as it allowed for more efficient use of network resources and increased throughput.

• Variable Subnet Support:

IGRP provided improved support for variable-length subnet masks (VLSM), allowing for more efficient use of IP address space and the ability to perform subnetting and supernetting in a more flexible manner.

• Reduced Routing Update Traffic:

IGRP implemented triggered updates in addition to periodic updates, which reduced unnecessary routing update traffic. Triggered updates meant that changes were propagated more quickly throughout the network, leading to faster convergence times after a network change.

• Network Stability Mechanisms:

To prevent routing loops and ensure network stability, IGRP utilized features such as split horizon, route poisoning, and holddown timers. These mechanisms improved the reliability of network routing by preventing the propagation of incorrect routing information.

• Ease of Configuration and Management:

For networks using Cisco equipment, IGRP was relatively easy to configure and manage due to its integration into Cisco’s IOS (Internetwork Operating System). This ease of use was particularly beneficial for network administrators familiar with Cisco environments.

Disadvantages of IGRP:

• Vendor Specific:

IGRP was a proprietary protocol developed by Cisco Systems. This meant that it could only be used on Cisco devices, limiting interoperability with equipment from other vendors. This vendor lock-in could lead to increased costs and limited flexibility in network design and equipment selection.

• Lack of Scalability:

Although IGRP improved upon RIP by supporting larger networks with its increased hop count limit, it still faced scalability issues in very large and complex networks. The protocol was not well-suited for the demands of rapidly expanding and evolving internet infrastructure.

• Slow Convergence:

IGRP could experience slow convergence times in larger networks or in networks with frequent topology changes. Slow convergence can lead to temporary routing loops and inconsistent routing tables, impacting network performance and reliability.

• Complex Metric Calculation:

The composite metric used by IGRP, while providing a more nuanced route selection process than RIP’s simple hop count, also introduced complexity in configuring and optimizing the network. Incorrect configuration of metric weights could lead to suboptimal routing decisions.

• Limited Support for Advanced Features:

As networking technology evolved, there was an increasing need for advanced features such as multiprotocol support, enhanced security, and improved traffic engineering capabilities. IGRP’s feature set did not fully meet these emerging requirements, leading to the development and adoption of more advanced protocols like EIGRP.

• Transition to EIGRP:

Cisco introduced Enhanced Interior Gateway Routing Protocol (EIGRP) as a successor to IGRP, incorporating support for more advanced features and improvements in efficiency and scalability. As EIGRP became the preferred choice for Cisco-based networks, IGRP was eventually deprecated, limiting its relevance and support.

• No Support for Non-IP Protocols:

Unlike its successor EIGRP, which was designed to be more protocol-independent, IGRP was primarily focused on IP networks. This limitation made it less versatile in environments where routing for multiple network layer protocols was necessary.

Key differences between IGRP and EIGRP

Key Similarities between IGRP and EIGRP

• Cisco Proprietary:

Both IGRP and EIGRP are proprietary protocols developed by Cisco Systems, meaning they were initially designed to be used on Cisco devices. This proprietary nature influenced their adoption and implementation in network environments primarily composed of Cisco equipment.

• Distance Vector Protocols:

At their core, both IGRP and EIGRP operate based on the distance vector routing protocol principle. They determine the best path to network destinations by sharing routing information with neighboring routers and calculating the distance to all possible destinations.

• Metric Components:

Both protocols use a composite metric that considers multiple factors to determine the best route. These factors include bandwidth, delay, reliability, load, and MTU (Maximum Transmission Unit). The use of a composite metric allows for more sophisticated route selection compared to simpler metrics like hop count.

• Routing for IP:

IGRP and EIGRP were both designed primarily for routing IP traffic. They are used to manage the routing of IP packets within an autonomous system, optimizing the path that data takes from source to destination.

• Load Balancing:

IGRP and EIGRP support load balancing, allowing network traffic to be distributed across multiple routes to optimize resource use and improve network performance. They can both perform unequal cost load balancing, although EIGRP’s implementation is more advanced.

• Automatic Route Summarization:

Both protocols automatically summarize routes at network boundaries, which can simplify routing tables and reduce the amount of routing information that needs to be exchanged between routers. However, EIGRP offers more flexibility with manual control over route summarization.

• Holddown Timers to Prevent Routing Loops:

IGRP and EIGRP use holddown timers as part of their mechanisms to prevent routing loops. These timers help stabilize the routing environment by preventing premature route changes.