An Explanation of the EIGRP
The Enhanced Interior Gateway Routing technology (EIGRP) was introduced in 1992 and is CISCO’s proprietary routing technology. This protocol is exclusive to CISCO routers because it is a CISCO proprietary protocol.
Below is a list of some of the most important things about EIGRP.
- RTP- Secure Data Transfer Protocol (RTP)
- Bounded Updates- Strictly limited updates—only routers that are impacted by a topology change will receive updates.
- It finds the optimum pathways by using the DUAL algorithm, which stands for “Difussion update algorithm.”
- By doing so, it forms adjacencies with nearby routers.
- It keeps track of the routing table, topology table, and neighbor table.
Even though EIGRP works in some ways like link-state routing protocols like OSPF, it is still a distance vector routing protocol.
The Algorithm
For the purpose of path determination and the upkeep of updated routes, EIGRP makes use of the DUAL algorithm as its engine. However, in contrast to other distance vector routing protocols, which employ the Bellman-Ford algorithm, this one does not. In the event that a change is identified in an EIGRP routing domain, the routers will communicate with one another in order to either construct redundant links or update themselves properly. In most cases, the updates that are performed by EIGRP are limited and partial. This means that in the event that a route is lost, the router will only tell the routers that are affected by the loss of the route, and it will only notify them of the absence of the route.
It is only the directly linked and impacted neighboring routers in the routing domain that receive the routing updates that are delivered using EIGRP. These updates are vectors of distance, and they are only sent within the routing domain.
Protocol-dependent modules (PDM)
Although it is most commonly used for routing IP traffic, EIGRP is capable of handling a wide variety of network layer protocols, including IPX, AppleTalk, and IP. The usage of Protocol-Dependent Modules (PDMs) enables this support.
Reliable Transport Protocol (RTP)
RTP (Reliable Transport Protocol) supports communications exchanged within an EIGRP routing domain. According to this protocol, the recipient of a certain message must send acknowledgement packets for each of the different messages. This protocol uses 224.0.0.10, which is the EIGRP multicast address, to operate.
Types of EIGRP Packets
To understand how EIGRP shares route information, you need to know what kinds of packets it uses. It is important to know that EIGRP uses 5 different kinds of packets to keep track of its connections. we’ll talk about them below:-
Hello packets
In the process of configuring EIGRP, the first packet that is transmitted is known as the Hello packet. This packet is transmitted in order to discover neighbors and establish adjacencies with those neighbors. When using slow networks, the hello packet is often transmitted at intervals of 60 seconds, while on links with bandwidth exceeding 1.544 megabits per second, such as T1 links, it is transmitted at intervals of 5 seconds.
An additional hold timer is included in the EIGRP hello packet. This hold timer is three times as long as the hello packet itself. Generally speaking, a router in an EIGRP routing domain is deemed to be down if it does not answer to three hellos. When hellos are responded to, it indicates that the routes are still operational.
One of the greatest methods for identifying EIGRP problems is to use the hello packet. Debugging commands can be used to determine the EIGRP problems.
Update
Routing information is communicated to neighbors in EIGRP through update packets. The updates are typically not sent unless there is a change in the topology. Depending on the severity of the observed topology change, EIGRP update packets are broadcast either unicast to just one router or multicast to multiple routers in the routing domain.
Acknowledgement (ACK)
A verification of whether or not updates or other sorts of messages were received is accomplished through the usage of ACK packets. Because of RTP, ACK messages are guaranteed to be transmitted using the reliable delivery method.
Query & Reply Packets
The query and reply packets’ job is to ask neighbors for lost routes when a router is missing one. Most of the time, requests are sent as multicast messages and replies are sent as unicast messages.
EIGRP and Routes propagation
At startup, EIGRP-configured routers typically broadcast hello messages to all domain routers, forming adjacencies; when neighbors respond, they establish neighbor connections. Once the routers have collected enough data, they will notify their neighbors through updates. To keep track of all the best and alternate routes, the routers compile a topology table. This is where the optimal route for packet forwarding is found.
