Subnet Query from Website

Hi,

Been practising subnetting from SubnetSkills site. Came across the following which to me seem wrong..

Question -you have the following address / mask -

172.18.0.0/255.255.240.0
What mask can be used for minimum of 32 subnets and maximum of 2 hosts. And it asks to optimize for number of subnets.
Now I put /30. But the site says /29. I have also pasted the sites explanation/answer which to me seems to contradict what they have put as the answer. Could someone confirm if I'm correct or if i'm wrong on this.

Solution from Site -

Solution:

This problem requires that you make some judgements about how to best subdivide a single network or subnet into multiple smaller subnets. You are presented with a network or subnet (172.18.0.0) and a prefix or subnet mask. If you are provided with a subnet mask, you will likely find it easier to start by converting the mask into a prefix. You were provided with a subnet mask, so converting it to a prefix results in a /20 prefix.

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Comments

DANMOH009

I would of answered it as /30 aswell bud, maximum of 2 hosts, to me is always /30. I dont know if the other agree with me, we possibly could be understanding the question wrong (not sure how though).

Dan

ChooseLife

control wrote: »

minimum of 32 subnets and maximum of 2 hosts. And it asks to optimize for number of subnets.

Ahhh, I see... I started typing that "/30" should be the right answer and then realized it says "2 hosts", not "2 nodes". Perhaps they want to have 2 hosts on the network plus the gateway, in which case a /29 would be required.

jude56g

ChooseLife wrote: »

Ahhh, I see... I started typing that "/30" should be the right answer and then realized it says "2 hosts", not "2 nodes". Perhaps they want to have 2 hosts on the network plus the gateway, in which case a /29 would be required.

I see what your saying here, but a /30 provides for a "maximum of 2 hosts" & it fulfills the requirement to "optimize for number of subnets"... a /30 mask will yield twice as many networks as a /29.

The thing that's really goofy about the question is that they ask for "2 hosts", and a "minimum" of 32 networks and give you a /20 to start with...

ChooseLife

jude56g wrote: »

I see what your saying here, but a /30 provides for a "maximum of 2 hosts" & it fulfills the requirement to "optimize for number of subnets"... a /30 mask will yield twice as many networks as a /29.

Given scarcity of information in the question, we have to make a decision whether two or three IP's are required per subnet.

My initial reaction was that it was two IP's, as that's what is stated in the question.

But upon reading it second time, I started thinking that the question implies 3 IPs - two for network "hosts" (not including router/gateway) + one for the router/gateway. In this case /29 is the smallest subnet fulfilling the requirement.

A good question, IMO, should not make the test taker choose between assumptions that lead to different answers.

jude56g wrote: »

The thing that's really goofy about the question is that they ask for "2 hosts", and a "minimum" of 32 networks and give you a /20 to start with...

I think it provides a tiny bit of an extra challenge to think outside of the byte-padded comfort zone...

Forsaken_GA

Bad question. A /29 allows for a maximum of 5 hosts. I would have answered a /30 as well, but then, I'm doing CCIE labs where the wording of the tasks is very specific and you ignore it at your own peril.

JockVSJock

I don't get this problem, if you are needing 32 hosts for a class b network, I would think 255.255.248.0 or /21 would work. Since this would give you 32 subnets.

Maybe I'm looking at this problem the wrong way.