Route summarization, which would cisco want?

Jasiono

I came across a scenario in my book and I was wondering what Cisco would want, because I always get scared when there are more than 2 possibly answers in scenarios. The way I learned summarization, the second option the author talks about is what I would use as my final answer, but he's saying option number 1 is "safer". Does Cisco want "Safer" or do they want the lowest possible route summary without being under? The image is attached from my ebook.

Jasiono

Here is the screenshot

cpartin

I don't consider the second answer correct. Technically yes it is a summary address for those networks but by that logic so is 172.16.0.0/16, 172.0.0.0/8, etc. In a lab I might use the 2nd option if I'm feeling lazy but never in production. I prefer to err on the side of being pedantic than to have some random routing issue crop up later.

EdTheLad

For CCNA you will not get a question like this, all summary questions will line up nicely on the bit boundary.
If this type of question appeared on the CCNP, it would ask it in 2 ways.
1) Which summary mask should be used to include all networks in the following range.
2) Which summary address should be used for the following range so that the upstream neighbor receives the minimum number of prefixes but can still route to all networks.

It's not a guessing game, read the wording of the questions carefully to understand the requirements.

Heero

As others have said, the test won't ask you a question like this without specifically giving you a requirement to do it one way or the other, and I doubt you would have a summarization question where they don't line up on bit boundaries on the CCNA. If Cisco had a question like this, they would basically be asking for the candidates opinion on how they would do the summary which is kind of pointless as either way works.

Jasiono

Nice thanks!

now that I read what you guys have said and looked into it a little further, it makes sense to have a summary about less hosts/networks and add the others to the table to make sure that there are no extra routes being summarized because a bigger block is being used.

crazboy84

I really dont like how that material you posted words things, just doesnt seem very cisco-y to me.

Jasiono

I'm skipping all the chapters on subnetting and summarization since I have the cbt nuggets and it's all I need. I was just curious as to how the author of the book went about explaining it. I cannot, for the life of me, learn any kind of math via text book. I have to be shown how to do calculations and such.