What is EIGRP?
Enhanced Interior Gateway Routing Protocol (EIGRP) is a proprietary routing protocol developed by Cisco. It builds upon the foundation of IGRP, delivering enhanced efficiency and scalability. EIGRP is a hybrid protocol that blends features of distance vector and link-state protocols. Its adaptability, support for IPv4 and IPv6, and robust convergence capabilities make it a popular choice for dynamic route management in medium to large networks.
How does EIGRP differ from IGRP?
EIGRP is an advanced version of IGRP, offering better performance and efficiency. Unlike IGRP, EIGRP supports faster convergence through the Diffusing Update Algorithm (DUAL). It uses more advanced metrics like bandwidth, delay, and load to compute paths, unlike IGRP's reliance solely on bandwidth and delay. EIGRP also supports Variable Length Subnet Masking (VLSM) and route aggregation, making it more versatile for modern networking needs.
What are the key features of EIGRP?
Key features of EIGRP include rapid convergence, efficient use of bandwidth, and support for unequal-cost load balancing. It uses a hybrid approach, combining distance vector simplicity with link-state efficiency. EIGRP employs the DUAL algorithm to optimize routing decisions and maintains three tables - routing, topology, and neighbor tables - for streamlined operation. Additionally, it supports multiple network layer protocols, route summarization, and reliable updates, making it both robust and scalable.
How does EIGRP combine the advantages of link-state and distance vector protocols?
EIGRP combines the simplicity of distance vector protocols with the efficiency of link-state protocols. Like distance vector protocols, EIGRP uses routing updates to maintain paths between networks. However, it adds efficiency by only sharing partial updates instead of entire tables. Its topology table and DUAL algorithm enable quick, loop-free convergence, a hallmark of link-state protocols. This hybrid approach ensures adaptability, scalability, and optimized performance.
What metrics does EIGRP use to calculate the best path?
EIGRP uses a composite metric that includes bandwidth, delay, load, reliability, and MTU (though MTU is not factored into calculations). Bandwidth and delay are the primary metrics, with bandwidth representing the slowest link along a route and delay reflecting the cumulative delay across all links. By combining these into a holistic assessment, EIGRP effectively selects the most optimal and reliable path for data transmission.
What is the role of the Diffusing Update Algorithm (DUAL) in EIGRP?
The Diffusing Update Algorithm (DUAL) is central to EIGRP, ensuring loop-free and fast convergence. It maintains a topology table with all possible routes, enabling rapid failover by pre-calculating backup routes. When a network change occurs, DUAL efficiently recalculates paths without having to rely on distance-vector reconvergence methods. This allows EIGRP to adapt to network changes dynamically while minimizing disruptions to traffic flow.
What is the purpose of EIGRP neighbors?
EIGRP neighbors are routers directly connected within a network that exchange routing information. The relationship between neighbors is established using hello packets, ensuring that routers can communicate and share updates efficiently. Neighboring routers collectively maintain the routing topology, allowing for rapid synchronization in case of changes. This partnership enables EIGRP to manage networks dynamically, ensuring the best routes are communicated and chosen.
What is the administrative distance of EIGRP?
The administrative distance (AD) of EIGRP is 90 for internal routes and 170 for external routes. AD defines the trustworthiness of a routing source, with lower values being more preferred. For comparison, RIP has an AD of 120, and OSPF uses 110, making EIGRP's internal routing highly reliable in mixed-protocol networks. This low AD contributes to quicker decision-making for EIGRP, ensuring prioritized data routing.
What is the difference between EIGRP internal and external routes?
EIGRP internal routes are learned within the same EIGRP autonomous system (AS) and have an administrative distance of 90. External routes come from sources outside the EIGRP AS and are redistributed into EIGRP, carrying an administrative distance of 170. Internal routes are considered more reliable and are prioritized over external routes when making routing decisions within the network.
How does EIGRP handle route redistribution?
EIGRP supports route redistribution, allowing routing information from other protocols, such as OSPF or RIP, to be incorporated. This process involves assigning external metrics to redistributed routes, enabling EIGRP to evaluate them for optimal connectivity. While redistributing, administrators can configure route maps, distribute lists, and filtering rules to control which external routes are accepted. This ensures seamless integration in multi-protocol environments.
What is the maximum hop count supported by EIGRP?
EIGRP's default maximum hop count is 100, but it can be manually configured to a limit of 255. This means EIGRP can support much larger networks compared to RIP, which has a fixed limit of 15 hops. Increasing the hop count allows EIGRP to work efficiently across extensive, complex network topologies while maintaining consistent performance and reliable route calculations.
How does EIGRP use autonomous system numbers?
Autonomous system (AS) numbers identify the scope of EIGRP processes within a network. EIGRP routers with the same AS number share routing information, creating an interconnected and cohesive routing environment. These numbers also isolate routing domains, ensuring that multiple EIGRP processes can function independently on the same router or network. Proper AS configuration is vital for accurate route sharing and avoiding conflicts.
How does EIGRP handle split horizon rules?
EIGRP adheres to split horizon rules by default, preventing a router from advertising a route back into the interface it was learned from. This minimizes the risk of routing loops and ensures stable path calculations. However, split horizon can be disabled in specific scenarios like hub-and-spoke configurations, where data must flow back to spokes. EIGRP provides flexibility in adapting split horizon based on network topology requirements.
What is the purpose of EIGRP route tagging?
EIGRP route tagging helps identify and manage routing information by attaching customizable tags to routes. These tags allow network administrators to classify and filter routes during redistribution or policy enforcement processes. For example, tagged routes can be isolated for specific domains or applications while ensuring critical paths are prioritized. Route tagging increases the granularity of route control, especially in large or multi-protocol networks.
How does EIGRP support IPv6?
EIGRP natively supports IPv6, using the same underlying mechanisms as in IPv4 but with adaptations for IPv6's expanded addressing format. It establishes neighbor adjacencies using IPv6 link-local addresses and advertises IPv6 prefixes in routing updates. EIGRP for IPv6 simplifies dual-stack environments by offering consistent features like fast convergence, load balancing, and reliable updates, enabling seamless transitions to modern network architectures.
What is the role of the topology table in EIGRP?
The topology table in EIGRP stores information about all possible routes to a destination. Unlike the routing table, which only holds active routes, the topology table also keeps feasible successors (backup routes). This allows EIGRP to quickly switch to a backup route if the primary path fails, ensuring minimal downtime and rapid convergence. By maintaining this comprehensive table, EIGRP optimizes both performance and reliability.
