Influence of EIGRP Route Selection Process

BD.

The reported distance (or advertised distance) is the cost from the neighbor to the destination.

It is calculated from the router advertising the route to the network.

For example in the topology below, suppose router A & B are exchanging their routing tables for the first time.

Router B says Hey, the best metric (cost) from me to IOWA is 50 and the metric from you to IOWA is 90 and advertises it to router A.

Router A considers the first metric (50) as the Advertised distance.

The second metric (90), which is from NEVADA to IOWA (through IDAHO), is called the Feasible distance.

The reported distance is calculated in the same way of calculating the metric.

By default (K1 = 1, K2 = 0, K3 = 1, K4 = 0, K5 = 0), the metric is calculated as follows:

Feasible successor is the backup route.

To be a feasible successor, the route must have an Advertised distance (AD) less than the Feasible distance (FD) of the current successor route.

Feasible distance (FD): The sum of the AD plus the cost between the local router and the next-hop router.

The router must calculate the FD of all paths to choose the best path to put into the routing table.

Note: Although the new CCNA exam does not have EIGRP topic but you should learn the basic knowledge of this routing protocol.

EIGRP (Enhanced Interior Gateway Routing Protocol) is a Cisco proprietary routing protocol that uses a complex algorithm to determine the best path to a destination network. The EIGRP route selection process takes into account a variety of factors to determine the most efficient route to the destination network.

Here are the explanations for the two actions that influence the EIGRP route selection process:

B. The router calculates the feasible distance of all paths to the destination route. Feasible distance is the metric that EIGRP uses to determine the best path to a destination network. Feasible distance is calculated by adding the cost of the outgoing interface to the advertised distance of the next-hop router. The router calculates the feasible distance for all available paths to the destination network and selects the path with the lowest feasible distance as the best path.

D. The router calculates the best backup path to the destination route and assigns it as the feasible successor. A feasible successor is a backup path to a destination network that can be used if the current best path fails. To be considered a feasible successor, the path must have a lower feasible distance than the current best path. The router calculates the feasible successors for all available paths to the destination network and selects the path with the lowest feasible distance as the best feasible successor.

A. The advertised distance is calculated by a downstream neighbor to inform the local router of the bandwidth on the link. The advertised distance is the metric that the next-hop router advertises to the local router. The advertised distance is calculated based on the bandwidth, delay, and reliability of the outgoing interface on the next-hop router. The local router uses the advertised distance to calculate the feasible distance for the path to the destination network.

C. The router must use the advertised distance as the metric for any given route. This statement is incorrect. The router does not use the advertised distance as the metric for any given route. The router uses the feasible distance as the metric to determine the best path to the destination network.

E. The router calculates the reported distance by multiplying the delay on the exiting interface by 256. This statement is incorrect. The router calculates the reported distance by multiplying the feasible distance by 256. The reported distance is the metric that the local router advertises to its neighbors. The reported distance is calculated by multiplying the feasible distance by 256 to make the metric a whole number.