🌠Day 1: All About IP Addresses
Imagine a courier is delivering you a parcel. He may ask for your street no and house number. To ensure the order reaches exactly at your doorstep, you must give your street and house number. 📦
ðŸ What is an IP Address?
In terms of networking, this street or house number is called the Internet Protocol (IP).
By this, the courier identifies you to deliver your parcel. Similarly, the server will find your device by its IP address to find you on the internet.
But wait, I sugar-coated it. It is not as simple as that! ðŸ˜ðŸ˜
🔢 IPv4 Structure
An IP has two types, IPv4 and IPv6. Here, we will talk about IPv4 for now.
An IPv4 address looks like this:
192.16.10.9
- Every decimal part is an Octet.
- Every decimal is exactly of one byte (8 bits).
- IPv4 has a total of 32 bits.
- Every decimal ranges from 0-255.
📊 IP Classes
IPv4 has three general classes for common usage. Their ranges are given below:
| Class | Range |
|---|---|
| A | 0.0.0.0 to 127.255.255.255 |
| B | 128.0.0.0 to 191.255.255.255 |
| C | 192.0.0.0 to 223.255.255.255 |
Note: Class D and Class E exist, but they are not exposed to the internet. They are for special use cases.
🌠Public vs Private IPs
There exist a total of roughly 4.3 billion IPv4 addresses, but the humans on Earth are about 8 billion, and every human has more than one device.
To assign every device a unique IP, we face a huge shortage. To avoid this, engineers made two types for IP assigning: Private and Public IPs.
🔒 Private IP
The IP assigned to a device within the LAN is a Private IP.
- Example: Devices connected to your home Wi-Fi router will have a Private IP which only the router knows.
Private IP is always changing for your device.
- If you connect now, your Private IP might be
192.168.125.1. - When you disconnect and connect again, it might be
192.178.12.12.
Classes of Private IPs:
| Class | Range | Usage |
|---|---|---|
| A | 10.0.0.0 to 10.255.255.255 |
Used by large million-dollar companies. |
| B | 172.16.0.0 to 172.31.255.255 |
Used by medium-sized organizations. |
| C | 192.168.0.0 to 192.168.255.255 |
Used in homes. |
🌠Public IP
The IP assigned to the router over the internet is a Public IP.
- Example: Your ISP will assign an IP to your router on lease to communicate over the internet. This leased IP is Public IP.
So, if your private IP matches another over the internet (which is possible), it doesn't affect your connection because your Public IP is different.
Is Public IP permanent for a router over the internet?
No, it changes but very slowly, or it depends on the ISP. For example, if you buy a monthly package, your router's IP might be the same for the whole month, or it may change when you restart the router or after the ISP's maintenance work.
Some public IPs may be permanent but for an extra cost (Static IP).
🔄 DHCP & NAT
Now, you might also be thinking, how do our devices get a Private IP? The answer is DHCP.
🤖 DHCP (Dynamic Host Configuration Protocol)
DHCP is a service that gives a device a Private IP.
- When you connect to a network, your device sends a DHCP Discovery message for available IPs.
- The DHCP server replies with an offer of an available IP.
- The device then sends a DHCP Request.
- The DHCP server assigns that IP to the device.
Remember: In LANs, the router acts as a DHCP server, while in WANs, there is a dedicated DHCP server.
🎠NAT (Network Address Translation)
NAT is a method for transforming Private IPs to Public ones.
Example:
- Router Public IP:
23.45.33.1 - Phone Private IP:
192.168.4.4 - Laptop Private IP:
192.168.3.1
Now, the router's NAT service translates these Private IP addresses to 23.45.33.1 when you make a request on the internet.
📠PAT (Port Address Translation)
You might ask: If every private IP address is translated to the same public IP in the same LAN through NAT, then how does the incoming data know which device made the request?
Answer:
When you make a search, the router doesn't simply do NAT (translate Private IP to Public). Instead, it creates a table using PAT.
This table contains the Private IP along with the port, and the translated IP and port.
| Device | Private IP & Port | Translated IP & Port |
|---|---|---|
| Device 1 | 192.168.123.1:5000 |
32.192.3.1:3000 |
| Device 2 | 192.168.34.3:5500 |
32.192.3.1:3001 |
| Device 3 | 192.168.3.1:5000 |
32.192.3.1:3002 |
So, in this way, ports are also translated, and the data goes to the exact location.
Difference between NAT and PAT:
NAT is an IP translator. PAT is an IP + Port translator.
In most LANs, what we call NAT is actually PAT.