Assigning Network Addresses to Subnet

Question

I'm currently looking over a textbook problem and I'm having trouble making sense of the answer.

The question is: Consider the topology shown here:

Denote the three subnets with hosts (starting clockwise at 12:00) as Networks A, B, and C. Denote the subnets w/o hosts as Networks D, E, and F.

Assign network addresses to each of these six subnets, with the following constraints: All addresses must be allocated from 214.97.254/17; Subnet A should have enough addresses to support 250 interfaces; Subnet B should have enough addresses to support 120 interfaces; and Subnet C should have enough addresses to support 120 interfaces. Of course, subnets D, E and F should each be able to support two interfaces. For each subnet, the assignment should take the form a.b.c.d/x or a.b.c.d/x – e.f.g.h/y.

and the answers are:

Subnet A: 214.97.255/24 (256 addresses)

Subnet B: 214.97.254.0/25 - 214.97.254.0/29 (128-8 = 120 addresses)

Subnet C: 214.97.254.128/25 (128 addresses)

Subnet D: 214.97.254.0/31 (2 addresses)

Subnet E: 214.97.254.2/31 (2 addresses)

Subnet F: 214.97.254.4/30 (4 addresses)

I have a few questions.

For subnet A, why would it be 214.97.255/24 and not 214.97.254/24?

For subnet B, how would you get the " - 214.97.254.0/29" part? Why wouldn't you be able to leave it as 214.97.254.0/25?

Lastly, for subnet F, why is it 4 addresses and not 2 like the others? (The question also states 2 addresses)

Answer 1

In my opinion; For subnet A, you can also use 214.97.254.0/24, in that case you need to allocate 214.97.255.0/24 for the rest of the network.

However, for the rest of your queries, I don't think the answer you gave is true. For example, When I tried configure following ip addresses in R2, it gives me an error as expected.

For Subnet E : address 214.97.254.2/31
For Subnet D : address 214.97.254.0/31
For Subnet B : address 214.97.254.58/25

While configuring Subnet B, it says it is overlapping as expected.

You would like to use 214.97.254.0/25 and 214.97.254.128/25 for Subnet B and C, each of which required 120 hosts. In that case, you need to spend all 254.0/25 and 128/25 for your subnet B and C network.

I did not get the idea behind doing 14.97.254.0/25 - 214.97.254.0/29 for your subnet B. If you want to spend 214.97.254.0/29 for your subnet D, E, and F, you need to divide your 14.97.254.0/25 address as 14.97.254.0/26 and 14.97.254.64/26, 14.97.254.0/27 and 14.97.254.32/27, 14.97.254.64/27 and 14.97.254.96/26, and so on.. Which makes each of them to be in different subnet. I think it should not be possible.

Can you check your textbook again?