What is EIGRP in Networking & EIGRP Characteristics and Features

What is EIGRP in Networking & EIGRP Characteristics and Features

This article is on what is EIGRP (Enhanced Interior Gateway Routing Protocol) and EIGRP Characteristics and Features. EIGRP is a classless vector distance routing protocol.

What is EIGRP?

The Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance vector routing protocol developed by Cisco Systems. As the name suggests, EIGRP is an improvement to another Cisco routing protocol: the internal gateway routing protocol ( IGRP ).
IGRP is a distance vector routing protocol with previous class, which became obsolete as of IOS 12.3.
EIGRP includes characteristics of the link state routing protocols. EIGRP is suitable for numerous different topologies and media. In a well-designed network, EIGRP can scale to include several topologies and can provide extremely fast convergence times with minimal network traffic.
EIGRP was originally launched in 1992 as an exclusive protocol available only on Cisco devices. In 2013, Cisco ceded basic EIGRP functionality as an open standard to the IETF, such as an informational RFC.
This means that other network providers can now implement EIGRP on their computers to interoperate with routers running EIGRP, either from Cisco or other manufacturers.
Note : in some older documents, the term “ hybrid routing protocol ” is used to define EIGRP. However, this term is misleading, because EIGRP is not a hybrid between distance vector routing protocols and link state protocols.

Characteristics and Features of EIGRP

EIGRP is based on the key principle of the distance vector routing protocol, according to which information about the rest of the network is obtained from directly connected neighbors.

• diffusing update algorithm

The diffusing update algorithm  (DUAL) is the center of the routing protocol. DUAL guarantees backup routes and no loops throughout the routing domain.
By using DUAL, EIGRP stores all available backup routes to destinations, so that it can be quickly adapted to alternative routes if necessary.

• Establishment of neighborhood adjacencies

EIGRP establishes relationships with directly connected routers that are also enabled for EIGRP. Neighborhood adjacencies are used to track the status of those neighbors.

• EIGRP Reliable Transport Protocol

The reliable transport protocol (RTP) is exclusive to EIGRP and is responsible for delivering EIGRP packages to neighbors.

• Partial and limited updates

Regarding your updates, the terms "partial" and "limited" are used in EIGRP. Unlike RIP, EIGRP does not send periodic updates, and route entries do not expire.
The term "partial" means that the update only includes information about route changes, such as a new link or a link that is no longer available.
The term "limited" refers to the propagation of partial updates that are sent only to those routers that are affected by the change.

• Load balancing of the same cost or with different cost

EIGRP supports load balancing of the same cost and load balancing with different costs, allowing administrators to better distribute the flow of traffic on their networks.

Protocol Dependent Modules

EIGRP has the ability to route several different protocols, including IPv4 and IPv6, through the use of protocol dependent modules (PDM).
PDMs are responsible for specific tasks of the network layer protocols. An example of this is the EIGRP module, which is responsible for sending and receiving EIGRP packets encapsulated in IPv4.
This module is also responsible for analyzing EIGRP packages and informing DUAL of the new information received. EIGRP asks DUAL to make routing decisions, but the results are stored in the IPv4 routing table.
PDMs are responsible for the specific routing tasks of each network layer protocol, including the following:

• Maintain the neighbor and topology tables of the EIGRP routers that belong to that protocol suite.
• Build and translate protocol-specific packages for DUAL.
• Connect DUAL to the protocol specific routing table.
• Calculate the metric and pass that information to DUAL.
• Implement filtering and access lists.
• Perform redistribution functions to other routing protocols and from them.
• Redistribute routes discovered by other routing protocols.

Reliable transport protocol

EIGRP uses the reliable transport protocol (RTP) for the delivery and reception of EIGRP packets.
EIGRP was designed as a network layer independent routing protocol and; Due to this design, you cannot use UDP or TCP services. This allows EIGRP to be used for protocols other than those in the TCP / IP protocol suite, such as IPX and Apple Talk . The illustration shows conceptually how RTP operates.

While the term "reliable" is part of its name, RTP includes reliable delivery and unreliable delivery of EIGRP packets, similar to TCP and UDP respectively.
Reliable RTP requires the receiver to send an acknowledgment to the sender. Unreliable RTP packets do not require acknowledgment.
For example, an EIGRP update package is sent reliably by RTP and requires an acknowledgment. An EIGRP greeting packet is also sent by RTP, but in an unreliable manner.
RTP can send EIGRP packets as unicast or multicast.

• EIGRP multicast packets for IPv4 use the reserved multicast IPv4 address 224.0.0.10.
• EIGRP multicast packets for IPv6 are sent to the reserved multicast IPv6 address FF02 :: A.

EIGRP Authentication

Like other routing protocols, EIGRP can be configured for authentication. RIPv2, EIGRP, OSPF, IS-IS and BGP can be configured to authenticate routing information.

It is advisable to authenticate the routing information that is transmitted. By doing so, it ensures that the routers only accept routing information from other routers that were configured with the same password or authentication information.

Note : Authentication does not encrypt EIGRP routing updates.