IP Address, Subnet Mask, Gateway, DHCP Service, and PPPoE Dial-Up

The advent of 5G technology has propelled the development of next-generation network communications. Home broadband speeds, which initially started at just a few dozen kilobits per second, have now surged to speeds of hundreds or even thousands of megabits per second. Many users who have deployed home NAS (Network Attached Storage) systems have even upgraded to 10Gbps internal local area networks. And now, the era of 6G is on the horizon.

In this age of interconnected information, mastering fundamental network knowledge is essential. Today, we will discuss five foundational concepts that are crucial for understanding:

1. IP Address
2. Subnet Mask
3. Gateway
4. DHCP Service
5. PPPoE Dial-Up

These concepts are frequently used in daily network configuration for computers or routers. In this article, I will explain them in a simple and engaging manner, avoiding technical jargon, to ensure you grasp these essential ideas.

01 What is an IP Address?

Let’s start with a question: Imagine a group of people in a closed room. What is the quickest way to call out to a specific person?

Most likely, your first thought would be to call their name, right?

Another simple method is to assign each person a number. For example, calling out “Number One” would indicate who you are referring to.

In the digital world, the same principle applies. To quickly access a specific device, each device needs a unique identifier, which is known as the IP address of the network device.

What happens if two people in the room have the same number?

Obviously, when that number is called, it becomes unclear who is being addressed. Therefore, a room cannot have two people with the same number.

Similarly, within a local network, no two devices can have the same IP address. If they do, it is called an IP conflict, which can severely disrupt network stability.

Now, let’s expand this scenario. Suppose there are multiple closed rooms in a building, each with a group of people. How do you locate a specific person in a particular room?

The answer is still through numbering. Each room is assigned a number, and within that room, each person is also numbered. For example, “Room 1, Number 1” would pinpoint the specific person.

In the context of network devices, an IP address like 192.168.1.100 can be understood as follows: 192.168.1 represents the room number, or the network segment we often refer to, and 100 is the identifier for the device within that segment.

02 What is a Subnet Mask?

Given the numbering scheme: 192.168.1.100, a new question arises:

Why is the room number 192.168.1, and the person’s number 100? Could we set the room number to 192.168 and the person’s number to 1.100 instead?

The answer is yes, but this would create ambiguity. The number 192.168.1.100 could then represent either the 100th person in Room 192.168.1 or the 1.100th person in Room 192.168.

To resolve this, we introduce another rule, the subnet mask, which tells us how many digits represent the room number and how many represent the person’s number.

Since the digital world operates on numbers, this rule is cleverly designed to be the same length as the numbering. By performing a bitwise AND operation with the numbering, it determines which part is the room number and which part is the person’s number.

For simplicity, let’s use an example:

The most common subnet mask, 255.255.255.0, means that the first three digits (255.255.255) represent the room number, and the last digit (0) represents the person’s number.

For instance, with the IP address 192.168.1.100 and the subnet mask 255.255.0.0, it indicates that 192.168 is the room number (or network segment), and 1.100 is the person’s number (or device identifier within that segment).

03 What is a Gateway?

Continuing from the previous scenario, each person in the closed room now has a unique number, which corresponds to the IP address of a network device.

But what if the people inside the room need to communicate with those outside?

In this case, a person with the ability to “teleport” between rooms is needed to relay messages. This person would take the messages from inside the room to the outside and bring back responses.

In the network world, this role is filled by the gateway, which is responsible for transmitting information from the internal network to the external network and vice versa. In a home network, this role is typically played by the router.

The router is the only device connected to the broadband, and all other devices in the home must go through the router to access the internet.

Therefore, the gateway in a home broadband network is the router. If the gateway is set incorrectly, it’s like trying to send a message through someone without the teleportation ability, and the message will not reach its intended destination.

04 What is DHCP Service?

From our previous understanding, we know how crucial a unique number is for each person. In a small room with just a few people, assigning numbers is straightforward, and everyone can choose their own number.

But imagine a large room with hundreds of people. If everyone chooses their own number, conflicts are bound to occur!

This is where a person with authority comes in.

This person assigns all the numbers, eliminating the need for individuals to choose their own, thus preventing conflicts. This service provided by the authoritative person can be called DHCP service.

As the saying goes, the capable should take on more responsibilities. Remember the person with the teleportation ability we mentioned earlier? If they were to assign the numbers, it would surely be accepted by everyone.

In a home broadband network, the DHCP service is usually provided by the gateway, which assigns an IP address to each device on the network.

05 What is PPPoE Dial-Up?

Continuing from the previous scenario, the person with the teleportation ability in each closed room has become the gateway, enabling communication between the room and the outside world. However, this only facilitates communication within a single building.

How can information be transmitted to a specific person in another building?

This is where a “god” who manages multiple buildings comes into play. This god can help relay messages to each building.

In other words, the person with the teleportation ability in each closed room hands over the communication messages to this god, who then delivers them to the intended recipients. This service provided by the god is akin to the home broadband service offered by telecom operators, which allows connection to the vast world outside, commonly known as the wide area network (WAN) or the internet.

Of course, communicating with the god is not straightforward. A dedicated channel is required.

This dedicated channel is established through PPPoE (Point-to-Point Protocol over Ethernet), a private communication channel between the person with the teleportation ability and the god.

This channel must be kept confidential and encrypted; otherwise, chaos would ensue. Therefore, authentication is required each time a connection is established, which is what we refer to as PPPoE dial-up for home broadband internet access.

And that concludes the explanation of the five fundamental network concepts.

Do you understand now?