This article is the final installment in a series of tutorials about VLSM. It all begins here.
Recall that from this table, many IP address ranges are still available on our network - everything from 192.168.10.0 through 192.168.29.0 for North America. For that reason, we can again subnet the address range further to account for the […]

Let’s start off by breaking our 192.168.0.0/16 network into 6 large subnets, since using the required 4 would only account for current regions, and would not allow for future growth. Doing this is not in any way different that what we’ve done in the past. To get 6 large subnets, we’ll need to steal 3 […]

At the most basic level, VLSM represents a hierarchical network addressing scheme. Think of it as subnetting multiple times within the same address range. For example, we can take the network 192.168.0.0 and subnet it into a number of large subnets. In our case, these will be used to define large geographic regions. Next, we […]

One thing that you may have noticed during our look at subnetting was that each and every subnet defined was exactly the same size, based on a single subnet mask value. While this is simple, it is again very wasteful. In most organizations, LANs are not all the same size. While some subnets may have […]

Recall that classful addresses are decidedly wasteful in the way they allocate addresses –even an entire Class B address range is too large for most companies. To make matters worse, a Class C block is so small that many companies would require many Class C ranges as a viable alternative. On the public Internet, routing […]

We spent time determining the valid ranges of addresses on a given subnet for a reason. Recall from our earlier look at TCP/IP communication that when a host wishes to communicate with another host, it must first determine whether the destination is local (on the same subnet) or remote (on a different subnet). In cases […]

If you’ve been watching closely, you may have noticed the very clear pattern that develops when attempting to determine address ranges. Now that we have the long method out of the way, we can take a look at a quick shortcut. With any given subnet mask value, there is always an associated multiple at which […]

To make things interesting, let’s go through what I consider to be a tough subnetting question. To be honest, if you can follow this question and understand what you’re doing, there isn’t a subnetting question I can ask that you can’t answer. We’re going to go through it step-by-step, just to be sure that you’re […]

Once you’ve managed to define a custom subnet mask that meets your requirements, the next step is calculating the ranges of IP addresses that are valid for a given subnet. Remember that after a custom subnet mask is defined, you have actually turned one big network address space into a number of smaller sub-network address […]

In this section we’re going to look at the process for custom subnetting Class A, B, and C network addresses. The good news is that the process is all just mechanics – if you follow the steps, you will always be able to define a custom subnet mask that meets your requirements.
When defining a custom […]