OVERVIEW AND CONCEPT OF EIGRP

overview                                           

Hello everyone, Hope you all having great time. well, this time i'm bring you something about routing protocol. so here we, Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco-proprietary routing protocol based on Interior Gateway Routing Protocol (IGRP). 

• firstly, IGRP is a classful routing protocol, where as EIGRP supports classless interdomain routing, Novell Routing Information Protocol (RIP) and AppleTalk Routing Table Maintenance Protocol (RTMP), serving both IPX and AppleTalk networks with accuracy and efficiency.
• Moreover, EIGRP is a hybrid routing protocol, offering the best of distance vector and link-state algorithms.
• Additionally, EIGRP is an advanced routing protocol that relies on features commonly associated with link-state protocols. Some of the best features of OSPF, such as partial updates and neighbour discovery are similarly put to use by EIGRP. However, EIGRP is easier to configure than OSPF.
• Also, EIGRP is an ideal,best, perfect choice for large, multi-protocol networks.
• This tutorial mainly covers up EIGRP configuration tasks. Mean while Particular attention is paid to the ways in which EIGRP establishes relationships with adjacent routers, how calculates primary and backup routes, and whenever there is need or any emergency situation , responds to failures in known routes to a particular destination.

So, we all know that A network is made up of many different type of devices, protocols, and media that allow data communication to happen around us. Basically, When one piece of the network does not work properly, users may be unable to communicate, or may be entire network may fail. If it's so then, In either case, the network administrator plays an important role here, he must quickly identify and troubleshoot problems when they arise. there can be lot of problem rather many kind of problems, like physical related to hardware or logical problem related to software. Network problems commonly result from the following:

• Mistyped or incomplete commands
• Incorrectly constructed or incorrectly placed access lists
• Misconfigured routers, switches, pc or other network devices
• wrong positioning of wires.
• Bad physical connections

So, one task completed that's we identified the problem in the network, it's strictly advised A network administrator should approach troubleshooting in a methodical manner that is in a effective manner, how this can be achieved.? this might be question in your mind. Well by using a general problem-solving model. In starting It is often useful to check for physical layer problems first and then move up the layers in an organized manner that is in a proper way. 

Troubleshooting of EIGRP include following:

• Troubleshoot a RIP routing process using show and debug commands
• Troubleshoot an IGRP routing process using show and debug commands
• Troubleshoot an EIGRP routing process using show and debug commands
• Troubleshoot an OSPF routing process using show and debug commands 

Correlation of EIGRP with IGRP   

how EIGRP And IGRP are related to each other, how they differ from each other, what are the similarities between them, what are the relation between them, these questions might be circling in your mind. Don't worry i'm gonna give you idea about it. Now it's time to discuss above, so here we go

• Cisco released EIGRP in 1994 as a scalable, improved version of its proprietary distance vector routing protocol, IGRP. The same distance vector technology found in IGRP is used in EIGRP, and the underlying distance information remains the same.
• EIGRP improves the convergence properties and the operating efficiency significantly over IGRP. This allows for an improved architecture while retaining the existing investment in IGRP.

Comparisons between EIGRP and IGRP fall into some major categories and we will quote them one by one, how one differ from other in each category. the following major categories:

• CM-Compatibility mode
• MC-Metric calculation
• HC-Hop count
• APR-Automatic protocol redistribution
• RT-Route tagging

1. first of all, as we know IGRP and EIGRP are compatible with each other. This compatibility provides seamless interoperability with IGRP routers following which  users can take advantage of the benefits of both protocols. EIGRP offers multiprotocol support, on the other hand IGRP does not.
2. secondly, EIGRP and IGRP use different metric calculations. Statistics show that EIGRP scales the metric of IGRP by a factor of 256. why?. That is because EIGRP uses a metric that is 32 bits long, and IGRP uses a 24-bit metric. Now here By multiplying or dividing by 256, EIGRP can easily exchange information with IGRP.
3. Thirdly, hope counts. IGRP has a maximum hop count of 255. EIGRP has a maximum hop count limit of 224. Actually, This is more than adequate to support the largest, properly designed internetworks.
4. let me make clear it may be you know what redistribution is or may be not. well it is used where we have two different routers and they want to share information with each other. means Enabling dissimilar routing protocols such as OSPF and RIP to share information requires advanced configuration.Redistribution, the sharing of routes, is automatic between IGRP and EIGRP as long as both processes use the same autonomous system (AS) number. below in Diagram , RTB automatically redistributes EIGRP-learned routes to the IGRP AS, and vice versa. 

EIGRP Vs IGRP

Excuse me folks, A very important point to remember about  EIGRP will tag routes learned from IGRP or any outside source as external reason behind is that they did not originate from EIGRP routers. IGRP cannot differentiate between internal and external routes.

Demonstration 

Now have look of above Diagram of output of show ip route command output. starting from Upper portion EIGRP router is flagged with Letter D. And external routers are specified with EX. RTA identifies the difference between the network learned via EIGRP (172.16.0.0) and the network that was redistributed from IGRP (192.168.1.0). In the RTC table, the IGRP protocol makes no such distinction. RTC, which is running IGRP only, just sees IGRP routes, despite the fact that both 10.1.1.0 and 172.16.0.0 were redistributed from EIGRP.