Can someone please explain the following, if I am wrong in my thinking? I am meant to be learning this from an online resource, but I think the resource is wrong. Here is the hypothetical situation:
A company is assigned a Class A network address of 220.127.116.11/8. The default subnet mask is 255.0.0.0. The company has the following minimum requirements:
1. Half the addresses must be reserved for future use.
2. Twelve networks are required with 8,190 hosts per subnet.
3. Ten networks are required with 2,046 hosts per subnet.
4. Five networks are required with 254 hosts per subnet.
The following are simplified steps to achieve a goal:
1. It instructs me to divide the network into two to meet requirement #1. Fine. Ok.
2. It instructs me to divide 1/2 of the network into 19 equals sized portions, as 13 bits are used for the host address (2 ^ 13 = 8,192) leaving 19 bits for the network address. Using the first 12 segments (Total: 18.104.22.168/19 to 22.214.171.124/19) gives me requirement #2.
The unused subnets, beginning with 126.96.36.199/19, can be reserved for future use or to meet subsequent requirements.
This is where I am either confused, or material is wrong.
3. Next, you need to create 10 networks with 2,046 hosts per subnet. Each of the preceding subnets yields 8,190. When subnetted, each can yield three subnets with 2,046 host addresses. To meet this requirement, you would need to create 10 subnets, which would require taking four of the networks developed earlier and subnetting them.
In other words, you must start where you left off, since you cannot have overlapping network addresses. The starting network address in this case is 188.8.131.52/19. You need 11 host bits to create 2,046 addresses. This means that you can use 21 network bits (32 – 11) to create these subnets. Table [the following] defines several of the starting network addresses, as well as the ending network address. The bits that represent the network ID are shown in bold.
Class A Subnet Address Binary Representation
[Here is what I think: ] Surely using the first 10 subnets, starting at 184.108.40.206/21, in increments of 0.0.8.0 would result in the last subnet used for this configurating being 220.127.116.11/21.
As before, you can select the first 10 subnets from this range to meet Requirement #3. The last subnet used in this configuration, then, is 18.104.22.168/21. The subnet mask is 255.255.248.0.
Am I doing something wrong, or is the material wrong? I'm hoping the former, which would prove I need education and that I've paid for a good service that will teach me well. If the latter, it may be time to shout at some people.
Thanks in advance, sorry for the length of the question.