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IPv4 Addressing

IPv4 Addressing

Author: Jacob Sorem

Basics of IPv4 addressing and subnetting, using a scenario

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IPv4 Basics

Basic overview of IPv4 Addressing

IPv4 Classes and Private IP Addressing

A quick look at the classes of IPv4 addresses and the limitations of each class. Understanding this helps us to understand why we subnet.

Note: I use Network ID below at a time which should be called Network Address. Technically Network ID is the information related to the network portion of the address, and Host ID the host. The Network Address is the first possible IP address in a network or subnet (sometimes referred to as the Subnet Address). Here's an example:

Network ID: 192.168.1
Host ID: 15
Network Address:

Sorry for any confusion.

Supplement to IP Addressing

In the above video, the classes for private IP addressing are mentioned.  These three, plus two more, can help define a nice set of information one might see on the Network+ Certification.  Here are the details of the five IPv4 addresses (in bold) I recommend memorizing and why they are helpful.

  • 10.     ___.___.___  Class A private
  • Starting Subnet Mask, /8 starting CIDR
  • 1 possible network (before subnetting)  16 million possible hosts (nodes) in the one network (before subnetting)
    • 126.___.___.___  End of the Class A range
  •  Loopback (the home machine)
    • 128.___.___.___  Start of the Class B range
  • 169.254.     ___.___  APIPA (Automatic Private IP Addressing, self assigning addresses when no DHCP is available)
  • 172.16-31.     ___.___  Class B private
  • Starting Subnet Mask, /16 starting CIDR
  • 16 possible networks (before subnetting)  65k possible hosts (nodes) in each network (before subnetting)
    • 191.___.___.___ End of Class B, 192.___.___.___ beginning of Class C
  • 192.168.0-255.     ___  Class C private
  • Starting Subnet Mask, /24 starting CIDR
  • 256 possible networks (before subnetting)  254 possible hosts (nodes) in each network (before subnetting)

Here's a handy table, in case you just want the 5 IP addresses and what they are.

IP address Description
10.___.___.___ /8 Class A Private Loopback
169.254.___.___ APIPA
172.16-31.___.___ /16 Class B Private
192.168.0-255.___ /24 Class C Private

With this information, it should be possible to answer most, if not all, IPv4 addressing related questions.

Subnetting as a concept

Before we get to the math, this is basically what subnetting is doing with a network address space.

The Math Behind Subnetting

Now that we understand the concept, it's time to calculate the specifics. Once we do this the hard way, we'll do it the easy way. (Note: the thumbnail image was taken in the middle of making changes. The Class A subnet mask does not match the binary. I hope this clears up any potential confusion.)

Subnetting Scenario

When trying to apply subnetting to a scenario, we need to ask some specific questions.

Calculating the Subnet We Need

Now that the network specifications are known, we can calculate the subnet mask and CIDR.

Final Application of the Subnet Calculator to the Scenario

Besides calculating the specific subnet mask and CIDR numbers, a subnet calculator can help with configuring the specifics of a network. These last three questions might be something you encounter when actually setting up a subnet in the enterprise environment.