What Is an IP Address?

An IP address can be either dynamic or static. A static address is a permanently assigned address. A static IP address that is assigned by an internet service provider is rare. You can assign static IP addresses to devices on your local network, but it can create network issues if you use it without a good understanding of TCP/IP.

Dynamic IP addresses are the most common. They're assigned by the Dynamic Host Configuration Protocol (DHCP), a service running on the network. DHCP typically runs on network hardware such as routers or dedicated DHCP servers.

A dynamic IP address is issued using a leasing system, meaning that the IP address is only active for a limited time. If the lease expires, the computer will automatically request a new lease. Sometimes, this means the computer will get a new IP address, too, especially if the computer was unplugged from the network between leases.

This process is usually transparent to the user unless the computer warns about an IP address conflict on the network (two computers with the same IP address). An address conflict is rare, and today's technology typically fixes the problem automatically.

Next, let's take a closer look at the important parts of an IP address and the special roles of certain addresses.

Earlier, you read that IPv4 addresses represent four eight-digit binary numbers. That means that each number could be 00000000 to 11111111 in binary, or 0 to 255 in decimal (base-10). In other words, 0.0.0.0 to 255.255.255.255.

However, some numbers in that range are reserved for specific purposes on TCP/IP networks. These reservations are recognized by the authority on TCP/IP addressing, the internet Assigned Numbers Authority (IANA). Four specific reservations include the following:

The other IP address reservations are for subnet classes. A subnetwork is a smaller network of computers connected to a larger network through a router. The subnet can have its own address system so computers on the same subnet can communicate quickly without sending data across the larger network.

A router on a TCP/IP network, including the internet, is configured to recognize one or more subnets and route network traffic appropriately. The following are the IP addresses reserved for subnets:

The first three (within Classes A, B and C) are those most used in creating subnets. Later, we'll see how a subnet uses these addresses. The IANA has outlined specific uses for multicast addresses within internet Engineering Task Force (IETF) document RFC 5771. However, it hasn't designated a purpose or future plan for Class E addresses since it reserved the block in its 1989 document RFC 1112. Before IPv6, the internet was filled with debate about whether the IANA should release Class E for general use.

Next, let's see how subnets work and find out who has those non-reserved IP addresses out on the internet.

The following is an example of a subnet IP address you might have on your computer at home if you're using a router (wireless or wired) between your ISP connection and your computer:

Besides reserving IP addresses, the IANA is also responsible for assigning blocks of IP addresses to certain entities, usually commercial or government organizations. Your internet service provider (ISP) may be one of these entities, or it may be part of a larger block under the control of one of those entities. When you connect to the internet, your ISP assigns you one of these addresses. You can see a full list of IANA assignments and reservations for IPv4 addresses at IANA's website [source: IANA].

If you only connect one computer to the internet, that computer can use the address from your ISP. Many homes today, though, use routers to share a single internet connection between multiple computers.

If you use a router to share an internet connection, the router gets the IP address issued directly from the ISP. Then, it creates and manages a subnet for all the computers connected to that router. If your computer's address falls into one of the reserved subnet ranges listed earlier, you're going through a router rather than connecting directly to the internet.

IP addresses on a subnet have two parts: network and node. The network part identifies the subnet itself. The node, also called the host, is an individual piece of computer equipment connected to the network and requiring a unique address. Each computer knows how to separate the two parts of the IP address by using a subnet mask. A subnet mask looks somewhat like an IP address, but it's actually just a filter used to determine which part of an IP address designates the network and node [source: Solarwinds].

A subnet mask consists of a series of 1 bits followed by a series of 0 bits. The 1 bits indicate those that should mask the network bits in the IP address, revealing only those that identify a unique node on that network. In the IPv4 standard, the most commonly used subnet masks have complete octets of 1s and 0s as follows:

People who set up large networks determine what subnet mask works best based on the number of desired subnets or nodes. For more subnets, use more bits for the network; for more nodes per subnet, use more bits for the nodes. This may mean using non-standard mask values. For instance, if you want to use 10 bits for networks and 22 for nodes, your subnet mask value would require using 11000000 in the second octet, resulting in a subnet mask value of 255.192.0.0.

Another important thing to note about IP addresses in a subnet is that the first and last addresses are reserved. The first address identifies the subnet itself, and the last address identifies the broadcast address for systems on that subnet.

Learning to distinguish between private and public IP addresses is important too. These classifications serve different purposes, both of which are fundamental to how devices communicate over the internet and within local networks [source: Mitchell].

Allocation and Registration

Public ip addresses are globally unique and must be registered wit the Internet Assigned Numbers Authority or a local internet registry. This is done to ensure that each public IP address is distinct and can be accessed over the internet.

On the other hand, private IP addresses are not registered or controlled by a central authority. They are allocated for use within private networks, like those found in homes, schools, and offices.

Accessibility and Scope

As mentioned above, a public IP address is accessible over the internet, which makes them essential for external network communication. They are assigned to devices that need to be directly accessible from outside the local network. This includes things like web servers, email servers, and routers that connect a local network to the web.

A private IP address allows multiple devices within the same network to communicate with each other. These addresses can't be accessed directly from outside the network.

Security and Cost

The public nature of public IP addresses necessitates careful management. Firewalls, intrusion detection systems, and other security measures are often necessary to protect devices with public IPs from unauthorized access by security threats.

Again, private IP addresses operate on a closed circuit, which creates a level of isolation that makes them safer. Moreover, since private IPs are freely available and reusable in different networks, they help conserve the limited supply of public IP addresses and reduce costs for organizations and individuals.

Few concepts are as central to modern communication as the internet protocol address. IP addresses enable devices from all over the globe to find and communicate with one another in the blink of an eye! Despite how far the internet has come, IP addresses remain indispensable cogs that enable the wheel of the internet to continue moving.

As you've learned, an IP address is a fundamental element that underpins the connectivity and functionality of our digital world. And, by unpacking the nature and function of IP addresses, we not only gain a deeper appreciation for the mechanics at play, but also empower ourselves to navigate and shape the communications landscape with more confidence.