Subnetting Class A and B Networks: IP Scheme and Calculations

This assignment provides a detailed guide to subnetting Class A and B networks, explaining the process of calculating network addresses, broadcast addresses, first usable IP addresses, and last usable IP addresses. It covers the steps involved in listing subnets, determining subnet sizes, increments, octets, and subnet masks using VLSM tables. The assignment also includes a practical example using a Class B network (144.12.0.0) with various subnet sizes, demonstrating how to allocate IP addresses for different subnets, including user subnets and WAN links. The example illustrates the calculations needed for each subnet, including the determination of network and broadcast addresses, and it addresses the special case where the addition of the increment results in an invalid value (256), providing the necessary adjustment. The assignment highlights the importance of decrementing order and proper IP scheme design to ensure efficient network configuration.

Subnetting with Class B and A Networks
Steps To Subnetting Class A or B Networks
1. List your subnets subnet size in order from largest to smallest.
2. Write down the starting IP address as the network address for your largest subnet, which is typically
the network address.
3. For each subnet, you should now be able to determine the subnet size, increment, octet and subnet
mask from the VLSM table provided you. Add that information to your IP scheme.
Calculating Network Addresses
4. Start on the first line, add the increment to the specified octet and write the result as the network
address for the subnet below. NEVER add the increment to line above or your IP scheme is wrong.
5. Continue this process for the remaining subnets until all of your network address are filled in. You
should actually have one extra network address after your last WAN link. That is good as it will be
used as part of the process.
Calculating Broadcast Addresses
6. Now calculate the broadcast address by subtracting one from the network address of the subnet that
follows it. Here's the process:
a. Start in the 4th octet, find the first octet that doesn't have a zero in it.
b. Subtract one from it and change all octets to the left to 255
c. Example: If 150.66.64.0 is the network address, the previous subnet ended at 150.66.63.255
7. Continue this process moving down the list of subnets until all octets have their broadcast address.
8. Calculating First Usable IP Address - Add 1 to the 4th Octet of the Network address.
9. Calculating Last Usable IP address - Subtract 1 from the 4th Octet of the Broadcast address.
***The only exception to this process is when calculating the network address and the result of your addition
produces the value 256, which is not valid. In this situation, change the value of that octet to 0 and add 1 to
the octet to its immediate left.
Example:
Subnet Size Increment/Octet Network Address Broadcast Address
100 Add 128 to 4th octet 144.12.0.0 144.12.0.127
90 128 in 4th octet 144.12.0.128 114.12.0.255
50 64 in 4th octet 144.12.1.0 144.12.1.63
144.12.1.64
When I added 128 to 128, I got 144.12.0.256, which cannot work. So I zero'ed out the 4th octet and added 1
to the third octet, resulting in 144.12.1.0

Example: You have a Class B network (144.12.0.0) with subnets of the following size:
5000, 1500 ,850, 150, 100, 75, 90, and 3 WAN links.
Step 1 – They are already decrementing order.
5000 hosts
A 5000 user subnet will be given 8192 host addresses. The table says that this subnet will jump by 32 in the
3rd octet, so the range of this subnet will be from 144.12.0.0 to 14.12.31.255 with a subnet mask of
255.255.224.0. In reality you will be creating 8 subnets of 8192, but we just calculated the range of the first.
1500 hosts
A 1500 user subnet will be given 2048 host addresses. The table says this subnet will jump by 8 in the 3rd
octet. We must remember that this subnet will pick up where the first one left off, starting at 144.12.32.0 and
ending at 144.12.39.255, with a SM of 255.255.248.0. In reality we broke up one chunk of 8192 into 4
chunks of 2048.
850 hosts
A 850 user subnet will be given 1024 host addresses. The table says this subnet will jump by 4 in the 3rd
octet. We must remember that this subnet will pick up where the first one left off, starting at 144.12.40.0 and
ending at 144.12.43.255, with a SM of 255.255.252.0. In reality we broke up one chunk of 2048 into 2
chunks of 1024.
150 hosts
A 150 user subnet will be given 256 host addresses. The table says this subnet will jump by 1 in the 3rd octet.
We must remember that this subnet will pick up where the first one left off, starting at 144.12.44.0 and
ending at 144.12.44.255, with a SM of 255.255.255.0. In reality we broke up one chunk of 1024 into 4
chunks of 256
100 hosts.
A 100 user subnet will be given 128 host addresses. The table says this subnet will jump by 128 in the 4th
octet. We must remember that this subnet will pick up where the first one left off, starting at 144.12.45.0 and
ending at 144.12.45.127, with a SM of 255.255.255.128. In reality we broke up one chunk of 256 into 2
chunks of 128.
90 Hosts
A 90 user subnet will be given 128 host addresses. The table says this subnet will jump by 128 in the 4th
octet. We must remember that this subnet will pick up where the first one left off, starting at 144.12.45.128
and ending at 144.12.45.255, with a SM of 255.255.255.128. In reality we broke up one chunk of 256 into 2
chunks of 128.
WAN Links
Wan links require only four IP addresses and always have a subnet mask of 255.255.255.252. Thus, we will
jump by 4 in the last octet. We left off at 144.12.46.0, so our WAN links will look like:
Size IP Addresses
Given
Increment/Octet Network
Address
Broadcast
Address
Subnet Mask
5000 8192 144.12.46.0 144.12.46.3
1500 144.12.46.4 144.12.46.7

850 144.12.46.8 144.12.46.11
150 144.12.46.12 144.12.46.15
100 144.12.46.16 144.12.46.19
90 144.12.46.20 144.12.46.23
WAN#1 144.12.46.24 144.12.46.27 255.255.255.252
WAN#2 144.12.46.28 144.12.46.31 255.255.255.252
WAN#3 144.12.46.32 144.12.46.35 255.255.255.252
Extra 144.12.46.36