Explained: How is My IP Assigned / Determined (IPv4)?

Infopackets Reader Izzy M. writes:

" Dear Dennis,

I am trying to figure out how IP addresses are assigned using IPv4 (IP addressing version 4), but can't seem to find a straight answer online. My question: is there a certain number that my IP address has to be? Is there any correlation between my IP address, subnet mask and default gateway? How is my IP address assigned or determined? Thank you in advance! "

My response:

I think the reason you can't find an answer to this question is because this is an extremely broad question. To put this as simple as possible: the answer to your question depends on your network class (A, B, C, D). The network class then determines whether you are referring to a public IP address which is assigned to your modem by your Internet provider, or a private IP address which is typically assigned by your router on a home network.

Related: How Do I Change my IP Address (IP Banned)?

Explained: How is My IP Assigned / Determined (IPv4)?

Your IP address (with respect to IPv4) is derived from three main things:

1. Your network class (A, B, C, D) - this defines whether you're using a public IP address (from your Internet provider) or a private IP address (typically assigned by your router, on your home network). For the record you can review a list of public IPs (IPv4) here.

2. The subnet, which defines how many IPs are assigned to the network class range

3. Whether the IP is leased or permanent (static or dynamic)

How an IP is Assigned on a Home Network (IPv4)

Let's look at a typical example for a home user.

Internet access is provided by an Internet Service Provider (ISP); data travels from the Internet to a modem inside your home (usually). A router connects to the modem and allows your home network to communicate to the outside world (to the Internet).

The router usually has DHCP (dynamic host control protocol) enabled by default. The purpose of DHCP is to automatically assign any device on your network an IPv4 address. This allows you to share the Internet across multiple devices in your home (or office), and even communicate with other devices across your entire private network.

Here's where things get a bit more technical.

The subnet mask is used to define a subnet range on the network. As a typical example, most routers are assigned a class C range. Class C is defined as having IPs 192.168.0.0 to 192.168.255.255, which yields a total of 2,097,150 usable IP addresses. This is far too large for most home networks; as such, a subnet mask is applied to yield a smaller range of usable IPs on the network.

Thus, a typical network class C range (for use at home) would be 192.168.0.1 to 192.168.2.254 with a subnet mask of 255.255.255.0, yielding 254 usable IP addresses. There is a mathematical way to derive how IPs are subnetted, which I will not get into - but you read read up on, if you want.

Of that IP range, certain IPs are reserved for special cases. For example:

• 192.168.0.1 is usually the default gateway (also used for the router administration page)
• 192.168.0.2 - 192.168.0.100 are usually reserved for dynamic addresses, controlled by DHCP; these IPs are leased and expire over time, thus DHCP IPs are not always the same
• 129.168.0.101 - 192.168.0.254 are usually reserved for static IPs
• 192.168.0.255 is the broadcast IP

Assigning an IPv4 Address: Using DHCP or Static IPs

On a typical home network, an IPv4 address is assigned depending on how the router and your machine are configured.

By default, DHCP (dynamic host control protocol) is enabled on the router. This means that the router will automatically assign an IP address to any device on the network automatically according to the DHCP IP range. The DHCP range is defined in the router administration page. Using the example above, the range would be 192.168.0.2 to 192.168.0.100.

If you prefer to set a static IP rather than one through DHCP, this would be done by adjusting your network adapter settings in the operating system. For example, if you have a 'server' or 'media pc' machine in the home and you want to use the same IP address for that device all the time (instead of a random IP address), then a static IP address makes more sense.

I hope this answers your question.

Keep in mind that this is an extremely broad question with many variables involved. That said, in the case of 'home networking' this answer should fit. In the case of how an IP is assigned using an Internet Provider: the same ideas apply, except DHCP is controlled by the Internet Provider and IPs are leased for a certain duration of time (especially if your modem or router loses power).

Related: How Do I Change my IP Address (IP Banned)?

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About the author: Dennis Faas is the owner and operator of Infopackets.com. With over 30 years of computing experience, Dennis' areas of expertise are a broad range and include PC hardware, Microsoft Windows, Linux, network administration, and virtualization. Dennis holds a Bachelors degree in Computer Science (1999) and has authored 6 books on the topics of MS Windows and PC Security. If you like the advice you received on this page, please up-vote / Like this page and share it with friends. For technical support inquiries, Dennis can be reached via Live chat online this site using the Zopim Chat service (currently located at the bottom left of the screen); optionally, you can contact Dennis through the website contact form.