IP Variable Length Subnet Masking (VLSM)

[csnorman]

Hello Everyone, I am taking a class in Network Infrastructure and I have been given a scenario to work on. I admit I am just a beginner and these are crash courses so I am a bit confused. Can someone help? If so here is the scenario:

Scope:
Research and report on why classful subnets have been replaced by VLSM.

Scenario:
A small company in Daytona has Wired Router using the Private IP address 192.168.1.0/24 and needs to create separate divisions for their company in 7 OUs using this address. They need to be able to connect to each division to the main office DCs
(2), a catalog web server, and file servers (2), and 8 workstations. Each OU will be protected by a single managed Vlan switch using the router (on a stick) and have its own subnet. The OUs computer accounts are;
1. Production 18 computers
2. Shipping 3 computers
3. Receiving 6 computers
4. Human Resources 2 computers
5. Accounts Receivable 4 computers
6. Accounts Payable/ Payroll 4 computers
7. MIS 2 computers
Using sub netting how can I create a subnet for each of these that will allow the ou subnets enough addresses?

If someone could help that would be awesome and I would like to know the whys to these answers. I want to learn as much as I can to get prepared better for testing.

Thanks so much,
csnorman

[Duki]

VLSM can be very challenging for new networkers. What you're doing is essentially subnetting subnets.

So for your example, if I understand it correctly, you have the following:

HQ - 13 computers
OUs - 39 computers/ea.

So to start, you want to being with the subnet that will require the most addresses (in this case, your OUs). So we start by determining the subnet that will allow for at least 39 usable IP addresses.

In this case, the subnet would be 192.168.1.0/26 (i.e., (32 - 6) because 6^2 = 64, and that is the closest possible to 39).

So now we list all of the subnets that will be used, for the OUs:
192.168.1.0
192.168.1.64
192.168.1.128
192.168.1.192
192.168.2.0
192.168.2.64
192.168.2.128

Now that we have the largest subnet out of the way we can start segmenting out subnet into smaller subnets, starting with 192.168.2.192

So for the HQ subnet, we only need 13 computers, so we'll use a /29 mask. This will give us:

192.168.2.192/29 (or 192.168.2.192 - 192.168.2.223)

I might not understand your question completely though.
For a more detailed description, have a look here. Hope this helps!

[csnorman]

Wow, Thank You for responding. I will look more at the info you gave me and see what more I can do.

[csnorman]

OK so can you explain to me what the Difference is using the simple method of creating IP address' and the VLSM way of creating IP differences. Just explain if possible without actually having to work it out if that makes since.