Remember, that in order to become a feasible successor it should meet the feasibility condition where its AD should not be greater than or equal to the successor’s FD. There is no feasible successor for this route. Let’s check Cannonball’s topology table: Cannonball#show ip eigrp topology Both are installed in the topology table and since they have the same FD both will be installed in the routing table. As you noticed, both have the same FD of 41024000. The first route is via the 192.168.102.2 of Porpita on the S2/0 or via the 192.168.103.3 of Cannonball on the s2/1 interface. There are 2 routes to go to 192.168.203.0 network. It uses the distance information, also known as a composite metrics to select efficient, loop-free paths. EIGRP uses DUAL to calculate the best path to a destination network. What is inside Nettle’s topology? Nettle#show ip eigrp topology Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance vector routing protocol designed by Cisco. Let’s verify the FD.Ĭhecking the interfaces: Nettle# show ip int brief Porpita#show ip int brief Cannonball#show ip int brief Let’s take a look at these three routers: Nettle, Porpita, and Cannonball. The feasible successor route will not be entered into the topology table if its AD is greater than the FD of the successor. This is because of the feasibility condition. Not all successors have a feasible successor. Since the idea of the successor, feasible distance, reported distance, and the feasible successor is clear to you, let me introduce the feasibility condition. It is the total cost from the local router to the destination. It is the route with the lowest metric in each network. Once you know the reported distance, you’ll find it easy to know the feasible distance (FD). Reported distance / advertised distance is the cost from the next hop router to the destination. So what is reported distance? Is it the same with advertised distance? Actually, they are just the same. Of course, the routing table has the best routes. Unlike feasible successor that can only be seen in the topology table, it is seen in the routing table. The successor is the best route to the destination. Now that you know the feasible successor, automatically you know what the successor is. It automatically chooses the feasible successor when successor route fails. It can be seen in the EIGRP topology table and because of this, the router doesn’t need to recalculate the metric. A feasible successor is a backup path used in the event the successor route disappears. And, that backup route is the feasible successor. Categories: Cisco, Routing EIGRP Successor and Feasible SuccessorĮIGRP really hates the querying process so it always preferred to have a backup route in case the link to a destination is unreachable.

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