Vlsm

I was answering a VLSM question on a Boson practice exam and had a question. I was always told when allocating IP addresses using VLSM, start with the subnet requiring the most hosts and work downward from there. In this example though, they start with the WAN link and seem to work up from there. Am I missing something?

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Comments

cpohlad

Actually I think I know the answer to my own question. The problem is, the question is multiple choice. The other answers are overlapping within the first range that would normally be allocated to the largest subnet.

Roguetadhg

cpohlad wrote: »

Actually I think I know the answer to my own question. The problem is, the question is multiple choice. The other answers are overlapping within the first range that would normally be allocated to the largest subnet.

Multiple choice VLSM hurts. Mostly because of the way it's tested. Drag and drop and multiple choice - yuck.

cpohlad

Yeah, it is just begging to get answered wrong. Just let us fill in the blanks!

boredgamelad

I know exactly the question you're talking about and in my opinion the way Boson tests you on VLSM is better for testing your knowledge of subnetting than letting you type in addresses yourself. The reason being exactly what you described. Being able to pick the correct /26, /27, and /30 (or whatever the options are) networks out of a given list tests not only your ability to allocate addresses but also to recognize network statements and masks that overlap or are otherwise incompatible. While I believe most people tend to allocate addresses starting with the largest subnet and working their way down, Todd Lammle makes a note in his CCNA guide that there's no required standard method. I personally liked that portion of the practice exam because it required me to think a bit more carefully about what I was doing.

cpohlad

There's a lot of validity to that. My first inclination was to immediately start with the largest number of hosts and work down. I guess my first inclination that things were not as they seemed was when the logical answer for the first subnet wasn't there.

boredgamelad

I had the same problem, so at least you're not the only one.