subnet questions n418 and n419

[Random73]

Ok these two drag and drop subnet questions both puzzle me for many reasons

1/ the questions ask for you to use subnet zero and to conserve host addresses for future use but both questions miss 4 host addresses when
allocating addresses to the serial interfaces n418 issues 192.168.91.197 to the serial link but the next usable host address is 192.168.91.193 so there is 4 missing hosts here and same thing occurs on question n419 where hosts 80-84 are not used

2/ when allocating hosts you should always issue your highest number of hosts to lowest so why does n419 allocate the 78 hosts their subnet last?

3/ going by the same principle of highest to lowest why does the serial link in n418 appear in the middle of the allocation?

4/ why is subnet zero not used in n418 if it is telling you it is in use?

this questions threw me off as they make no sense whatsoever and come with no explanation of how the answer was arrived at


please explain  ???

[umericanboy]

You are confused alright 

Both questions are designed this way to make you do some calculations and not give you a "gimme" answer. The 4 hosts were missed in n418 so you can find out which subnet do they belong to and whether it's not a network ID. I think you are wasting your time looking at the IPs, just look at the # of host each subnet provides and assign that CIDR to the appropriate port. It's a lot easier that way and will save you time on the test.

[Random73]

so what you are saying is to ignore the fundamental rules of subnet assignment and just make it up as you go along rather than follow any set pattern that is set so that trouble shooting of a network is made easier?

why does the question state you have to leave as many addresses for future use as you can and then waste 4?


so your answer while I understand the makes you calculate thing is also wrong as it is not following the guidelines set by cisco or the question itself

[umericanboy]

what I'm saying is that leave the fundamental rules for the REAL world. For the test, you have to go with the answer that is provided to you and following the best possible solution, you have to pick one of those answers. You can say that the question was worded wrong by whoever wrote the question but you still have only the given options to choose from. If this was a SIM question, then you would use your fundamental rule of subnetting, not when the options are given to you. 

[Random73]

ok I have just passed the CCNA exam and as I suspected I did get a very similar question to these but it followed the proper guidelines set by cisco so I think these two questions need changed