4.1 IP Addresses and Routing
In the previous module, we learned that DNS helps translate human-readable names into technical information that computers can use.
When someone types a domain name such as:
michaelisuniversity.com
DNS helps find the information needed to reach the correct destination. However, finding a destination is only part of the process. Once a device knows where it wants to go, it still needs a way to get there. This is where IP addresses and routing become important.
DNS helps answer the question:
“Where is the destination?”
Routing helps answer the question:
“How do we get there?”
Together, IP addressing and routing allow data to travel across networks and reach the correct destination.
What Is an IP Address?
An IP address is a numerical address used to identify a device on a network.
IP stands for Internet Protocol.
Internet Protocol is one of the core communication standards that makes the Internet possible. Among other things, it provides a system for identifying devices and helping data move between them.
A simple way to think about an IP address is as a mailing address. If someone wants to send you a letter, they need an address.
Similarly, if one computer wants to send information to another computer, it needs some way to identify where that information should go. That identifying address is called an IP address.
For example, a device might have an address that looks like:
192.0.2.15
Computers use these numerical addresses to identify destinations and exchange information across networks. Without addresses, devices would have no reliable way to know where information should be delivered.
IPv4 and IPv6
Today, two major versions of IP addresses are used on the Internet.
These are called:
- IPv4
- IPv6
IPv4 stands for Internet Protocol Version 4.
IPv4 addresses are the familiar addresses made of four groups of numbers separated by periods.
For example:
192.0.2.15
When the Internet was first developed, IPv4 provided a very large number of possible addresses. At the time, few people imagined that billions of phones, computers, televisions, game consoles, sensors, cameras, vehicles, and other devices would eventually connect to the Internet.
As the Internet grew, the world began running out of available IPv4 addresses. To help solve this problem, a newer addressing system called IPv6 was developed.
IPv6 addresses are much longer and can support a vastly larger number of devices.
An IPv6 address might look something like:
2001:db8::15
IPv6 was designed to provide enough addresses for the continued growth of the Internet.
Today, both IPv4 and IPv6 are widely used. Many modern websites and services support both.
Public and Private IP Addresses
Not every IP address is visible to the entire Internet. Some addresses are public. Some are private.
A public IP address is an address that can be reached from the Internet.
A private IP address is used inside a local network.
For example, imagine a home network. Your laptop, phone, smart television, printer, and tablet may all have private IP addresses assigned by your home router. These devices can communicate with each other within the home network. The router then acts as a gateway between the local network and the larger Internet.
From the perspective of the Internet, many devices inside the home may appear to share a single public IP address provided by the Internet service provider.
This arrangement helps conserve public IP addresses and is common in homes and businesses around the world.
Networks and Routers
An IP address identifies a destination.
A router helps data move toward that destination.
A router is a networking device that connects networks together and helps direct traffic between them.
We have already encountered routers briefly in previous modules when we discussed how packets move across the Internet.
Routers are one of the reasons the Internet can connect billions of devices spread across countless networks.
Imagine driving across a country. You may pass through many intersections before reaching your destination. At each intersection, you decide which road to take next.
Routers perform a similar role for Internet traffic. They receive packets and help determine where those packets should go next.
What Is Routing?
Routing is the process of determining the path that data takes across networks.
When you open a website, send an email, stream a video, or use an app, the information involved is typically divided into packets.
Those packets may travel through many networks before reaching their destination.
Each router along the path examines information in the packet and helps decide where it should be sent next.
This decision-making process is called routing.
The Internet does not have one giant map controlled by a single organization. Instead, many routers operated by many different organizations cooperate to move traffic across the world. This is one reason the Internet is often described as a network of networks.
Routing Tables
How does a router know where to send a packet?
One important tool is something called a routing table.
A routing table is a collection of information that helps a router decide where traffic should go.
A simple way to think about a routing table is as a set of directions.
Imagine someone asks:
“How do I get to this city?”
A map or navigation system helps answer the question.
Similarly, a routing table helps routers determine the next step in a packet’s journey.
Routing tables may contain manually configured routes, routes learned from other routers, and information about nearby networks. They do not necessarily know the entire path from beginning to end. Instead, they often make the best next decision based on the information available to them.
As packets move through the Internet, many routers work together to guide them toward their destination.
How a Packet Finds Its Destination
Let us put everything together.
Imagine that someone opens a website. The process might look something like this:
- The user enters a domain name into a browser.
- DNS helps find the IP address associated with that domain.
- The browser creates requests that are divided into packets.
- Routers examine the packet information.
- The packets move through multiple networks.
- The destination server receives the packets.
- The server sends packets back to the user.
Most of this happens in fractions of a second.
The user sees a webpage load. Behind the scenes, routers, IP addresses, DNS systems, servers, and networks are all working together.
Why Routing Matters
Routing is one of the hidden systems that makes the Internet possible.
Without routing, data could not reliably travel between networks. Websites would not load. Email would not arrive. Streaming services would not work. Cloud applications would not function.
Modern communication depends on the ability to move packets efficiently across a massive global network.
Routing is also important for reliability.
If one path becomes unavailable, traffic can often be redirected through other routes. This flexibility helps the Internet continue operating even when equipment fails, cables are damaged, or networks experience problems.
Looking Ahead
So far we have learned how the Internet was created, how websites work, how DNS helps users find online destinations, and how IP addresses and routing help data travel across networks.
However, we now come to new questions:
Who actually provides Internet connectivity?
Who owns the networks that carry traffic?
Who connects homes and businesses to the wider Internet?
How do thousands of separate networks cooperate to create a global communication system?
In the next section, we will examine Internet service providers, network tiers, peering, and the organizations that help keep the modern Internet connected.