Longest match vs Metric vs Administrative distance ??? I thought Longest Match was most important

[Pabsgc]

This is from my CCNA mock exams on Udemy, as far as i knew from credible sources, the 1st and most important thing was Longest match rule (specificity) THEN AD and then lastly metric... I keep getting contradicted with this. Any help is appreciated

[Giuseppe Larosa · Accepted solution]

Hello @Pabsgc ,

exam questions test also understanding of english language even at CCNA level.

Here the question state that multiple routes exist from the same routing protocol -> this means all the routes will be with the same Administrative distance.

Also it is supposed that these routes represent the same prefix / prefix length . They used this idea to choice the correct answer.

In reality:

your understanding is correct the most specific prefix is used first.

when dealing with specific routing protocols like OSPF you will discover that it has different route types and that there is a hierarchy in these route types ( O intra area routes are preferred over O IA inter area routes that are preferred over O E1 external routes that are preferred over O E2 routes).

This question focuses on the IP routing table where in square brackets you have the [AD/metric].

Hope to help

Giuseppe

[Pabsgc]

Ok thanks for the answer,

I dont understand why its "supposed" that they routes advertised would have the same prefix length??

[Jon Marshall · Accepted solution]

It's because the wording says multiple routes to the same destination ie. the assumption being it would only be the same destination if it had exactly the same mask as well. 

Personally I find these questions are not testing your knowledge or understanding, they are just trying to catch you out. 

Your understanding is fine, don't let these type of questions cause you to doubt yourself. 

Jon

[Pabsgc]

Ah right, I didn't know same destination meant the prefix was exactly the same but thanks for clearing that up.