• Best VPN Service

    Top VPNs that Unlock Netflix, provide Secure Torrenting, Strong Encryption, Fast Downloads, DNS Leak Protection, Identity Protection and have Cheap VPN prices.

    read more

    Hyper-V Concepts

    It's time to get familiar with Hyper-V Virtualization, virtual servers, virtual switches, virtual CPUs, virtual deployment infrastructure (VDI) and more.
    Read more

Hot Downloads

Subnetting - Bits & Analysis. Learn to Recognise the Number of Bits in a Subnet Mask

Posted in Subnetting

So we have covered to some depth the subnetting topic, but there is still much to learn ! We are going to explain here the available subnet masks and analyse a Class C network, using a specific subnet mask. It's all pretty simple, as long as you understand the logic behind it.

Understanding the use, and analysing different subnet masks

Okay, so we know what a subnet mask is, but we haven't spoken (yet) about the different values they take, and the guidelines we need when we use them. That's what we are going to do here !

The truth is that you cannot take any subnet mask you like and apply it to a computer or any other device, because depending on the random subnet mask you choose, it will either create a lot of routing and communication problems, or it won't be accepted at all by the device you're trying to configure.

For this reason we are going to have a look at the various subnet masks so you know exactly what you need to use, and how to use it. Most important, we are going to make sure we understand WHY you need to choose specific subnet masks, depending on your needs. Most people simply use a standard subnet mask without understanding what that does. This is not the case for the visitors to this site.

Let's first have a look at the most common subnet masks and then I'll show you where these numbers come from :)

Common Subnet Masks

In order to keep this place tidy, we are going to see the common Subnet masks for each Class. Looking at each Class's subnet mask is possibly the best and easiest way to learn them.

Numer of bits
Class A
Class B
Class C
0 (default mask)
255.0.0.0 (default_mask)
255.255.0.0 (default_mask)
255.255.255.0 (default_mask)
1
255.128.0.0 (default +1)
255.255.128.0 (default+1)
255.255.255.128 (default+1)
2
255.192.0.0 (default+2)
255.255.192.0 (default+2)
255.255.255.192 (default+2)
3
255.224.0.0 (default+3)
255.255.224.0 (default+3)
255.255.255.224 (default+3)
4
255.240.0.0 (default+4)
255.255.240.0 (default+4)
255.255.255.240 (default+4)
5
255.248.0.0 (default+5)
255.255.248.0 (default+5)
255.255.255.248 (default+5)
6
255.252.0.0 (default+6)
255.255.252.0 (default+6)
255.255.255.252 (default+6)
7
255.254.0.0 (default+7)
255.255.254.0 (default+7)
255.255.255.254 (default+7) * Only 1 Host per subnet
8
255.255.0.0 (default+8)
255.255.255.0 (default+8)
255.255.255.255 (default+8) * Reserved for Broadcasts

The above table might seem confusing at first, but don't despair ! It's simple, really, you just need to look at it in a different way!

The trick to understanding the pattern of the above table is to think of it in the following way: Each Class has its default subnet mask, which I have noted using the Green colour, and all we are doing is borrowing a Bit at a time (starting from 1, all the way to 8) from the Host ID portion of each class. I have used various colours to show you the decimal numbers that we get each time we borrow a bit from the Host ID portion. If you can't understand how these decimal numbers work out, then you should read up on the Binary & IP page.

Each time we borrow a bit from the Host ID, we split the network into a different number of networks. For example, when we borrowed 3 Bits in the Class C network, we ended up partitioning the network into 8 smaller networks. Let's take a look at a detailed example (which we will break into three parts) so we can fully understand all the above.

We are going to do an analysis using the Class C network and 3 Bits which we took from the Host ID. The analysis will take place once we convert our decimal numbers to binary, something that's essential for this type of work. We will see how we get 8 networks from such a configuration and their ranges !

ip-subnetting-mask-bits-1

In this first part, we can see clearly where the 8 Networks come from. The rule applies to all types of Subnets, no matter what Class they are. Simply take the Subnet Bits and place them into the power of 2 and you get your Networks.

Now, that was the easy part. The second part is slightly more complicated and I need you focused so you don't get mixed up!

At first the diagram below seems quite complex, so try to follow me as we go through it:

ip-subnetting-mask-bits-2

The IP Address and Subnet mask is show in Binary format. We focus on the last octet which contains all the information we are after. Now, the last octet has 2 parts, the Subnet ID and Host ID. When we want to calculate the Subnets and Hosts, we deal with them one at a time. Once that's done, we put the Subnet ID and Host ID portion together so we can get the last octet's decimal number.

We know we have 8 networks (or subnets) and, by simply counting or incrementing our binary value by one each time, we get to see all the networks available. So we start off with 000 and finish at 111. On the right hand side I have also put the equivalent decimal number for each network.

Next we take the Host ID portion, where the first available host is 0 0001 (1 in Decimal), because the 0 0000 (0 in Decimal) value is reserved as it is the Network Address (see IP Classes page), and the last value which is 1 1111 (31 in decimal) is used as a Broadcast Address for each Subnet (see Broadcast page).

Note

I've given a formula in the IP Classes page that allows you to calculate the available hosts, that's exactly what we are doing here for each subnet. This formula is :2 to the power of X -2. Where X is the number of Bits we have in the Host ID field, which for our example is 5. When we apply this formula, we get 2 to the power of 5 - 2 = 30 Valid (usable) IP Addresess. If you're wondering why we subtract 2, it's because one is used for the Network Address of that subnet and the other for the Broadcast Address of that subnet. This shouldn't be new news to anyone :)

Summing up, these are the ranges for each subnet in our new network:

ip-subnetting-mask-bits-3

ip-subnetting-mask-bits-4

I hope the example didn't confuse you too much; the above example is one of the simplest type, which is why I chose a Class C network, they are the easiest to work with.

If you did find it somewhat difficult, try to read over it slowly. After a few times, you will get to understand it. These things do need time to sink in!

Next - Routing and Communications Between Subnets

Subnet Masks & Their Effect

Posted in Subnetting

Introduction

There are a few different ways to approach subnetting and it can get confusing because of the complexity of some subnets and the flexibility they offer. For this reason I created this little paragraph to let you know how we are going to approach and learn subnetting. So.....

We are going to analyse the common subnet masks for each Class, giving detailed examples for most of them and allowing you to "see" how everything is calculated and understand the different effects a subnet mask can have as you change it. Once you have mastered this, you can then go on and create your custom subnet masks using any type of Class.

Internet Protocol Classes - Network & Host ID

Posted in IP Protocol

This article explains the 'Network-ID' and 'Host-ID' concept found in IP addressing and subnetting. We analyse the structure of IP addresses and network classes and show their Network-IDs and Host-IDs in binary format to make evident how the system works.

To help understand the network class analysis, we show examples of well-known ip address ranges and calculate their valid networks and hosts depending on their class and subnetmask.

The information provided in this article is extremely important for engineers who want to really understand IP addressing and subnetting.

Every protocol suite defines some type of addressing that identifies computers and networks. IP Addresses are no exception to this "rule". There are certain values that an IP Address can take and these have been defined by the IEEE committee (as most things).

A simple IP Address is a lot more than just a number. It tells us the network that the workstation is part of and the node ID. If you don't understand what I am talking about, don't let it worry you too much because we are going to analyse everything here :)

IP Address Classes and Structure

When the IEEE committee sat down to sort out the range of numbers that were going to be used by all computers, they came out with 5 different ranges or, as we call them, "Classes" of IP Addresses and when someone applies for IP Addresses they are given a certain range within a specific "Class" depending on the size of their network.

To keep things as simple as possible, let's first have a look at the 5 different Classes:

ip-classes-1

In the above table, you can see the 5 Classes. Our first Class is A and our last is E. The first 3 classes ( A, B and C) are used to identify workstations, routers, switches and other devices whereas the last 2 Classes ( D and E) are reserved for special use.

As you would already know an IP Address consists of 32 Bits, which means it's 4 bytes long. The first octet (first 8 Bits or first byte) of an IP Address is enough for us to determine the Class to which it belongs. And, depending on the Class to which the IP Address belongs, we can determine which portion of the IP Address is the Network ID and which is the Node ID.

For example, if I told you that the first octet of an IP Address is "168" then, using the above table, you would notice that it falls within the 128-191 range, which makes it a Class B IP Address.

The Internet Protocol (IP) Header

Posted in IP Protocol

This article examines the Internet Protocol (IP) and its position within the OSI Model. We take a look at the IP Header and all fields contained within an Ethernet frame. Further examination of the IP header is covered in the next pages that follow.

CCENT/CCNA

Cisco Routers

  • SSL WebVPN
  • Securing Routers
  • Policy Based Routing
  • Router on-a-Stick

VPN Security

  • Understand DMVPN
  • GRE/IPSec Configuration
  • Site-to-Site IPSec VPN
  • IPSec Modes

Cisco Help

  • VPN Client Windows 8
  • VPN Client Windows 7
  • CCP Display Problem
  • Cisco Support App.

Windows 2012

  • New Features
  • Licensing
  • Hyper-V / VDI
  • Install Hyper-V

Linux

  • File Permissions
  • Webmin
  • Groups - Users
  • Samba Setup