Enhanced Interior Gateway Routing Protocol, abbreviated as EIGRP, refers to a network protocol that basically enables routers to perform an exchange of information more efficiently compared to earlier network protocols, like the Interior Gateway Routing Protocol or Border Gateway Protocol.
In this article, we will look more into the EIGRP according to the GATE Syllabus for (Computer Science Engineering) CSE. We will read ahead to find out more about it.
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What is EIGRP?
A hybrid routing protocol developed by Cisco that combines link-state and distance-vector capabilities is called Enhanced Interior Gateway Routing Protocol (EIGRP). It operates on protocol number 88 at the network layer.
Features of EIGRP
Here are some of the features of EIGRP:
Rapid convergence: A DUAL method is used by EIGRP to support quick convergence. A possible successor route can be employed if a network’s access route fails. A query message is disseminated to determine an alternate route to that network if there isn’t a route to it in the topology table as well.
Reduced bandwidth usage: In contrast to other distance vector routing protocols, EIGRP does not deliver recurrent updates. EIGRP uses partial updates if there is any change in the topology, i.e. updates are triggered if only any event occurs, thus consuming the bandwidth whenever needed. Distance vector routing protocols like RIP send full routing tables over a period of time, thereby consuming the available bandwidth needlessly. Additionally, EIGRP updates are only sent to the routers that demand them.
Support all WAN and LAN protocols and topologies: EIGRP supports all WAN topologies such as leased lines, point-to-point links, as well as multi-access networks like a token ring, FDDI, etc. There is no additional configuration needed for layer 2 protocols such as frame relay when using EIGRP.
Supports auto-summary: Auto-summarisation is by default enabled in EIGRP. Routers will automatically receive summarised routes thanks to a technology called auto summation, which enables routing protocols to automatically summarise their routes for their classful networks, EIGRP. For example, 1.1.1.1/24 will be automatically summed to 1.1.1.1/8.
Supports unequal cost load balancing: EIGRP allows for the variance value to be changed to achieve unequal cost load balancing. Variance is set to 1 by default, which provides equal-cost load balancing. But if we want to make use of unequal-cost load balancing, we may adjust the value of variance based on how much traffic we want to distribute among various paths. The feasible distance is multiplied by a factor greater than the feasible distance of the successor.
Communication via RTP: RTP, a proprietary protocol, is used by EIGRP to control communication between the EIGRP-speaking routers. 224.0.0.10 is the multicast address used by EIGRP. The router builds and keeps a list of routers for each multicast it broadcasts (speaking EIGRP). 16 unicast messages are used to send the same data if a multicast acknowledgement is not received. It is deemed dead if an acknowledgement is not received even after 16 unicast attempts. Reliable multicast is the name given to this procedure.
Best path selection using DUAL: The Diffusing Update Algorithm (DUAL) is used by EIGRP to determine the optimal path open to a network. All of the routes to the network are maintained in a topology table by EIGRP-speaking routers. The second-best path (possible successor) from the topology database is used if the best path or successor declines. It sends a query message that resolves the query if there is no path present in the topology table.
It mostly maintains three different tables:
(a) Neighbour table: It includes details about the routers that have developed a neighbourly relationship. It also includes the SRTT and RTP. Additionally, it includes the queue count figure for the greetings that go unanswered.
(b) Topology table: It includes all of a network’s available routes, both feasible successor and successor.
(c) Routing table: It includes every route that is currently used to guide routing decisions. These paths are regarded as being the successor (best path) routes.
Traffic control: Let’s say we don’t want an interface on the router that is connected to an ISP to be a part of the EIGRP process. EIGRP offers a functionality that allows us to flag the interface as passive in this situation, which means that it will not participate in the EIGRP process.
- Provide support for Variable Length Subnet Mask.
- Both IPv4 and IPv6 support.
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