Powers of 2 are important to understand and memorize for use with IP subnetting.

To review powers of 2, remember that when you see a number with another number to its upper right (called an exponent), this means you should multiply the number by itself as many times as the upper number specifies.

For example, 2 power of 3 is 2 × 2 × 2, which equals 8. Here’s a list of powers of 2 that you should commit to memory:

2 power of 1 = 2
2 power of 2 = 4
2 power of 3 = 8

2 power of 4 = 16
2 power of 5 = 32
2 power of 6 = 64
2 power of 7 = 128
2 power of 8 = 256
2 power of 9 = 512
2 power of 10 = 1,024
2 power of 11 = 2,048
2 power of 12 = 4,096
2 power of 13 = 8,192
2 power of 14 = 16,384

Before you get stressed out about knowing all these exponents, remember that it’s helpful to know them, but it’s not absolutely necessary. Here’s a little trick since you’re working with 2s: each successive power of 2 is double the previous one.

This is 7 OSI layers you should to know and understand before start to learn the next step of networking. Follow me to learning now!

Application Layer
The seventh layer, or topmost layer, of the OSI Reference Model is the application layer. It provides the interface that a person uses to interact with the application. This interface can be command-line-based or graphics-based. Cisco IOS routers and switches have a command-line interface (CLI), whereas a web browser uses a graphical interface.

Note : that in the OSI Reference Model, the application layer refers to applications that are network-aware. There are thousands of computer applications, but not all of these can transmit information across a network. This situation is changing rapidly, however. Five years ago, there was a distinct line between applications that could and couldn’t perform network functions.

A good example of this was word processing programs, like Microsoft Word they were built to perform one process: word processing. Today, however, many applications–MicrosoftWord, for instance–have embedded objects that don�t necessarily have to be on the same computer. There are many, many examples of application layer programs. The most common are telnet, FTP, web browsers, and e-mail.

The International Organization for Standardization (ISO) developed the Open Systems Interconnection (OSI) Reference Model to describe how information is transferred from one machine to another, from the point when a user enters information using a keyboard and mouse to when that information is converted to electrical or light signals transferred along a piece of wire or radio waves transferred through the air. It is important to understand that the OSI Reference Model describes concepts and terms in a general manner, and that many network protocols, such as IP and IPX, fail to fit nicely into the scheme explained in ISO’s model.

Therefore, the OSI Reference Model is most often used as a teaching and troubleshooting tool. By understanding the basics of the OSI Reference Model, you can apply these to real protocols to gain a better understanding of them as well as to more easily troubleshoot problems.

ISO developed the seven-layer model to help vendors and network administrators gain a better understanding of how data is handled and transported between networking devices, as well as to provide a guideline for the implementation of new networking standards and technologies. To assist in this process, the OSI Reference Model breaks the network communication process into seven simple steps.

Step 6: Figure Out the Host Addresses

Step 6 is the easiest step. If you recall, any address between the network and directed broadcast address is a host address for a given network. We can then complete the rest of our addressing for 192.168.1.0, as is shown in table as below.

If you look at the very first subnet in this table, 192.168.1.0, you’ll see that it has a total of 14 host addresses, which matches are formula: 2 power of Y - 2, 2 power of 4 - 2 = 14 hosts. For the CCNA Exam, you will need to understand how to do IP addressing.

Of course, on the job, you can cheat and use an IP subnet calculator.

Step 5: Figure Out the Directed Broadcast Addresses

After figuring out all of your subnets, you next need to figure out what the directed broadcast address is for each subnet.

This is very simple. The directed broadcast of a subnet is one number less than the next network number.

Also, the broadcast address has all of its hosts bits set to binary 1s. Table as below shows our network numbers and directed broadcast addresses.

For the last table entry, the directed broadcast address will be the highest possible value in a byte: 255.

Next go to step 6 to planning your ip address here.

Step 4: Figure Out the Network Addresses

In step 4, we need to figure out the networks that we created with our new subnet mask. Since IP addressing is done in binary, network addresses will always increment in a multiple of something. We’ll use this to our advantage when figuring out what our network numbers are for our Class C network.

Remember that the network number has all of the host bits set to 0s.

Actually, we already know what this multiplier is: we figured this out in the second part of step 2, using the 2 power of 4 - 2 = 14 formula. The 14 value is the number of valid host values for a subnet; however, this is not the total number of addresses for the subnet.

The subnet also has a network and broadcast address, which is the reason the formula subtracts 2 since you can’t use these addresses for host devices. Therefore, in our example, each network has a total of 16 addresses, and is incremented by 16 from subnet-to-subnet.

There is another method of verifying your multiplying value. In a byte, you can have numbers ranging from 0 - 255, resulting in a total of 256 numbers.

Step 3: Figure Out the Subnet Mask

Now that the hardest part is over, the rest of the four tasks is easy. At this point, you now know the number of subnet bits you need. However, when dealing with networking and subnet masks, a subnet mask’s network portion contains both network and subnet bits. Here’s a reminder of the default number of networking bits for a class address: A is 8, B is 16, and C is 24.

Given this, just add the class address bits to the subnet bits, and this gives you the total number of networking bits. In our example, this would be 24 + 4 = 28. To make the remaining three steps easier, I recommend that you convert the number of bits of the subnet mask to a dotted decimal mask. However, this is not too hard of a process.

First, remember that a subnet mask, just like an IP address, is represented in a dotted decimal format, where there are 8 bits in each octet. That means, for a Class C mask, the first 24 bits are set to 1. In other words, the mask at least begins with 255.255.255.

Step 2: Satisfy Host and Network Requirements

In the second step, you’ll use three formulas:

1. 2 power of X => number of networks you need (X represents subnet bits)
2. 2 power of Y - 2 => number of hosts on your largest segment (Y represents host bits)
3. X + Y <= total number of host bits

In the first step, you need to figure out how many bits you need to steal from the host bits to create your subnets. In the second step, you need to figure out how many host bits you need to accommodate your host requirements. And last, you need to make sure that when you add up the bits that you stole for subnets, and the bits that you need for your hosts, that you didn’t exceed the original number of host bits that you started out with, based on the class A, B, or C network.

As an example, if you had a Class C network and were subnetting it and needed 5 bits for subnets and 4 bits for hosts, this would total 9 bits. Unfortunately, Class C networks only have 8 host bits to begin with, so this wouldn’t work. In this situation, you would either need a Class B network or 2 Class C networks.

Step 1: Figure Out Network and Host Requirements

In this step, you need to do two things:

- Determine the number of hosts that do, or will, exist on the largest segment in your network.
- Determine the maximum number of segments that you have in your network–this will tell you how many networks, or subnets, you’ll need.

If you already are dealing with an existing network, then you have a lot of analysis ahead of you. You’ll need to perform the above two tasks, counting hosts on each segment, and the number of segments that you have.

Remember that when you are counting hosts, each device with a connection to the segment needs to be counted this includes PCs, servers, routers, servers, printers, and other devices. Remember that a segment could be used in a logical sense, like all the ports off of a switch, or a VLAN.

To assist with the remaining 5 steps, You’ll create an imaginary network. This network has 14 segments and the largest segment has 14 devices on it. You’ve been assigned a single class C network number (192.168.1.0).

Now you’re ready to proceed to step 2 of ip address planning.