Implementing EIGRP for IPv4

By | June 14, 2020

Following is the topology for our network to configure EIGRP.

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In EIGRP we should pick an autonomous system (AS) number for our network no matter whether it is large or small. This AS number must have to match in all the routers sharing EIGRP.
RIP
 is time based protocol where if it does not hear a “hello” message from its neighbor for 90 seconds it make changes in the routing protocol. However, EIGRP & OSPF are triggered based protocols no matter how long you do not listen from your neighbor but if there is any change in neighbor the router gets knowledge of it, whether the router goes down or the interface changes or any other change happens the router gets trigger immediately.
There is only one time check  that is done after 15 minutes if nothing happens on link and this is just to know the neighbor is fine.

In EIGRP if you do not provide subnet mask then the network address will be considered as class-full.

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This command will be considered as class-full and the network will be assign of class C. So if you are using VLSM you have to have provide subnet mask in wild card fashion as shown below.

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Configuring EIGRP for R1, R2, and R3

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R2 Configuration

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Notice that R2 has learned from its neighbor R1 immediately.

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Notice that the flag of EIGRP is represented by D. It is because Cisco has reserved E for EGP which was developed prior to EIGRP. The D represents the DUAL algorithm of EIGRP.

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Now if we see the routing table of R1, it will have EIGRP routing entries.

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Notice that [90/5376] is the metric that protocol calculated 90 autonomous number and 5476 is bandwidth of the route.

Notice that the ping is successful from R3 to R1.

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Now configure other 3 routers and check connectivity.

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Notice that there is connectivity from R6 to R1.

The routing changes occur very quickly in this protocol if the interface goes down the router knows it within a second.

EIGRP Database

EIGRP holds two routes to the destination if there are two links, which there are in our topology. The protocol builds a database and place two routes in the database one is primary which is called successor route and other is secondary which is called feasible route. When the primary routing interface goes down the protocol immediately picks the backup route (feasible route) and puts in charge to transmit data.

As shown in above diagram where 192.168.0.0/24 and 192.168.1.0/24 networks route learned from interface Fa0/0 and Fa0/1. This is because we are using packet tracer and metrics of links are same. So one is primary route and other is secondary if primary goes down the secondary take the charge immediately.

We can see the database to know which route is successor and which is feasible successor.

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This database shows us all information regarding routes. This database is almost identical because this was created using packet tracer. We need to look at another fluctuated database to understand this.

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The FD stands for feasible distance which means the actual distance from router itself to the destination router and the value 28928 show that the Gigabit1/0 interface is the successor route and other is feasible route for 192.168.3.0/24 network.

(28928 / 28672) the first metric is the feasible distance and the second is the advertised distance. Advertised distance is the distance that the neighbor shows us from itself to destination. It is not surprising that FD wins AD.

Debugging

This feature tells the changes in the routing protocol and helps to troubleshoot the network.

Command : debug ip eigrp

Lab Topology

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Prerequisites for 200-301

200-301 is a single exam, consisting of about 120 questions. It covers a wide range of topics, such as routing and switching, security, wireless networking, and even some programming concepts. As with other Cisco certifications, you can take it at any of the Pearson VUE certification centers.

The recommended training program that can be taken at a Cisco academy is called Implementing and Administering Cisco Solutions (CCNA). The successful completion of a training course will get you a training badge.

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