Exam 200-301 topic 1 question 360 discussion

OSPF uses cost to make routing decisions

It is C. Anyone disputing this needs to study

For those who's didn't understood the A answer : router take fact that he calculate the metric of the source router wich is not possible, because this behavior seems like a distance vector protocol behivior, ospf is a link state protocol so this is a wrong answer. The good answer is C

C is correct

A is incorrect because it says to pick the route with the lowest bandwidth, it should be with the highest bandwidth. The higher the bandwidth, the less the cost

Isn't A specifically for the outdated IGRP? with keywords "metric from source router"?

OSPF-running routers use these criteria to select the best route to be installed in the routing table: When there are multiple routes available to the same network with different route types, routers use this order of preference (from highest to lowest): Intra-area routes Inter-area routes External Type-1 routes External Type-2 routes If there are multiple routes to a network with the same route type, the OSPF metric calculated as cost based on the bandwidth is used for selecting the best route. The route with the lowest value for cost is chosen as the best route. If there are multiple routes to a network with the same route type and cost, it chooses all the routes to be installed in the routing table, and the router does equal cost load balancing across multiple paths.

C says how to calculate ospf metric for a specific intf A says how to choose the correct path to dest with the lowest cumulative metric. A is correct answer.

c is correct

definitely is C

A takes every exiting interface from source to destination into account C Only takes 1 exiting interface into account Cumulative cost is the sum of the all costs of the outgoing OSPF interfaces in the path. While calculating cumulative cost, OSPF consider only outgoing interfaces in path. It does not add the cost of incoming interfaces in cumulative cost. If multiple routes exist, SPF compares the cumulative costs. Route which has the lowest cumulative cost will be chosen for routing table. https://www.computernetworkingnotes.com/ccna-study-guide/ospf-metric-cost-calculation-formula-explained.html

I would go for A The destination could be after several hops ,and each of those has a cost based on BW , they needed do be all added to calculate the cost to that destination

C : Cisco routers determine what to base the cost versus bandwidth on a 'reference bandwidth' which defaults to 100mbps. The reference bandwidth is then divided by the link bandwidth to generate the link cost

In fact C is misleading. This is because cost compared is not the cost of one interface (obtained by division of ref BW/interface BW). It is rather the accumulation of all the divisions on all interfaces, e,g. if the first interface 100Mbps ==> cost=1 and the second interface is 10 Mbps==> Cost =10, the total cost is 10+1=11, which is the one compared with the total costs of other paths calculated similarly. Hence, I would choose A as it is more descriptive of the process except for that last 2 words "lowest bandwidth" is incorrect and should be "lowest cost".

to be specific, its not actual bandwidth, its the reference bandwidth :)

C is correct. https://networktechstudy.com/home/learning-ospf-path-selection