🔢 Understanding IPv4 Addresses in Depth

🤔 What is an IPv4 Address?

An IPv4 address is a 32-bit number that serves as a unique logical identifier for a device on a network. It’s how devices find each other across the internet.

• Format: It is written as four decimal numbers separated by dots, known as dotted-decimal notation. Each number is called an octet.
• Example: 172.16.254.1
• Range: Each octet can be a number from 0 to 255. This format allows for 2³² (about 4.3 billion) unique addresses.

🧩 The Two Parts of an IP Address

Every IPv4 address is made of two parts:

1. Network ID: The first part of the address that identifies the specific network a device is on. All devices on the same local network share the same Network ID.
2. Host ID: The second part of the address that identifies the specific device (or host) on that network. Each host on the same network must have a unique Host ID.

Analogy: Think of the address Park Street, House No. 10.

• Park Street is the Network ID.
• House No. 10 is the Host ID.

🎭 The Subnet Mask: The Divider

A subnet mask is a 32-bit number that tells a device which part of its IP address is the Network ID and which part is the Host ID.

• How it Works: The 255s in a subnet mask correspond to the Network ID, while the 0s correspond to the Host ID.
• Example:
  • IP Address: 192.168.1.10
  • Subnet Mask: 255.255.255.0
  • This mask tells us the Network ID is 192.168.1 and the Host ID is 10.

📜 IP Address Classes (The Traditional System)

Historically, IPv4 addresses were grouped into classes. While modern networking uses a more flexible system (CIDR), understanding classes is fundamental.

• Class A (1.x.x.x to 126.x.x.x)

  • Structure: Network.Host.Host.Host
  • Default Mask: 255.0.0.0
  • Use: For extremely large networks owned by entities like major international corporations.

• Class B (128.x.x.x to 191.x.x.x)

  • Structure: Network.Network.Host.Host
  • Default Mask: 255.255.0.0
  • Use: For medium-to-large networks, like universities.

• Class C (192.x.x.x to 223.x.x.x)

  • Structure: Network.Network.Network.Host
  • Default Mask: 255.255.255.0
  • Use: For small networks. The vast majority of home and small office networks in India use a Class C private address range.

🔒 Special and Reserved IP Addresses

Not all IP addresses are assignable to devices. Some are reserved for special purposes.

• Private IP Addresses: These ranges are reserved for use inside private networks (LANs) and are not routable on the public internet.

  • 10.0.0.0 to 10.255.255.255 (Class A)
  • 172.16.0.0 to 172.31.255.255 (Class B)
  • 192.168.0.0 to 192.168.255.255 (Class C) - Extremely common in home routers.

• Loopback Address: 127.0.0.1. This address always refers to the local machine itself, also known as “localhost.” It’s used for testing.

• Network & Broadcast Addresses:

  • Network Address: The first address in a range (where the host part is all zeros, e.g., 192.168.1.0). It identifies the network itself and cannot be assigned to a device.
  • Broadcast Address: The last address in a range (where the host part is all ones, e.g., 192.168.1.255). It’s used to send a message to all devices on the network at once.

🛡️ Private vs. Public IP Address (with CGNAT)

To understand how our many devices access the internet, it’s crucial to know the difference between the two main types of IP addresses and how they are managed.

🌍 Public IP Address

A Public IP address is the single address assigned to your network by your Internet Service Provider (ISP). This is the address that the rest of the internet sees when you go online.

• Scope: Global and routable on the public internet.
• Uniqueness: It must be globally unique. No two networks can have the same public IP address at the same time.
• Assigned By: Your ISP (e.g., Jio, Airtel, BSNL).
• Analogy: Think of it as the main postal address of your entire office building.

✅ Benefits

• Direct Accessibility: A device with a public IP can be directly reached from anywhere on the internet. This is essential for hosting public services like a website, an email server, or a game server.
• Uniqueness: A public IP provides a clear, unique identity on the global network, which simplifies direct communication between two points without the complexities of NAT.

❌ Drawbacks

• Security Risk: Being directly exposed to the internet makes a device a visible target for hackers, automated scans, and other malicious attacks. A robust firewall is non-negotiable.
• Scarcity and Cost: Public IPv4 addresses are a finite resource and have been completely allocated. This scarcity means they have a cost, and ISPs must manage them carefully, leading to practices like CGNAT.

🏠 Private IP Address

A Private IP address is the address assigned to each individual device within your local network (LAN) by your router.

• Scope: Local only. It is not routable on the public internet.
• Uniqueness: It only needs to be unique within your own LAN. The same private address (e.g., 192.168.1.100) can be used in millions of different homes.
• Assigned By: Your home router.
• Analogy: Think of it as the specific cubicle number for an employee inside the office building. It’s only relevant internally.

✅ Benefits

• Enhanced Security: This is the primary benefit. Devices on a private network are not directly reachable from the internet. The router’s NAT acts as a natural firewall, protecting internal devices from external threats.
• Address Conservation: By allowing millions of private networks to reuse the same address ranges (like 192.168.x.x), private IPs were the main solution to the IPv4 exhaustion problem.
• Free and Simple: Private IP ranges are free to use, and routers automatically manage their assignment via DHCP, making local network setup easy.

❌ Drawbacks

• Indirect Accessibility: You cannot directly connect to a device with a private IP from outside the local network. This makes hosting servers or remotely accessing a specific device more complex, requiring configurations like Port Forwarding.
• NAT Complications: Relying on NAT can sometimes cause problems for peer-to-peer applications, online gaming, and VoIP. If your ISP uses CGNAT (Double NAT), it becomes nearly impossible to set up direct inbound connections.

🔄 How They Work Together: NAT (Network Address Translation)

So how do all your devices with private IPs communicate with the internet using only one public IP? The answer is NAT (Network Address Translation), a process managed by your router.

NAT acts like a receptionist for your network:

1. Outgoing: When your phone (private IP 192.168.1.5) wants to access a website, the request goes to your router. The router replaces the private IP with its own public IP and sends the request to the internet.
2. Incoming: When the website responds, it sends the data back to your router’s public IP. The router then checks its records, sees that the request originally came from your phone, and forwards the data to the correct private IP (192.168.1.5).

🏢 What is CGNAT? (Carrier-Grade NAT)

Due to the global shortage of IPv4 addresses, many ISPs in India (especially mobile and some broadband providers) have taken NAT a step further with CGNAT.

• What it is: CGNAT is a large-scale NAT performed by the ISP itself. Instead of assigning a unique Public IP to your router, the ISP assigns your router a private IP from their own network (often in the 100.64.x.x range).
• How it works: Your router does NAT for your home, and then the ISP’s router does a second layer of NAT for hundreds or thousands of customers, who all share a single Public IP. This is often called Double NAT.
• Analogy: Imagine a large IT park (the ISP) with many different company buildings (customers). Each building has its own receptionist (your router doing NAT). But all mail leaving the IT park goes through a central mailroom (the ISP doing CGNAT), which puts the single address of the IT park on all outgoing mail.
• Impact: CGNAT makes it very difficult to run personal servers, host games, or access security cameras from outside your home network, as you don’t control the final layer of address translation.

✨ Quick Comparison

🔄 Dynamic vs. Static IP Address

The terms “dynamic” and “static” refer to how an IP address is assigned to a device. This applies to both public and private IP addresses.

🌊 Dynamic IP Address

A Dynamic IP address is an address that is automatically assigned to a device on a temporary basis. It can, and often does, change over time.

• How it Works: This process is managed by a DHCP (Dynamic Host Configuration Protocol) server. When a device connects to a network, it requests an IP address, and the DHCP server “leases” one to it from an available pool. When you restart your router or your lease expires, your ISP may assign you a new public IP.
• Common Use: This is the default for most devices. Your laptop and smartphone get dynamic private IPs from your router, and most residential internet plans in India (from providers like Jio or Airtel) provide you with a dynamic public IP.

✅ Benefits

• Automatic & Easy: No manual setup is required. It’s a plug-and-play system.
• Cost-Effective: ISPs can efficiently manage their limited pool of IPv4 addresses by reassigning them to customers who are currently online.

❌ Drawbacks

• Unreliable for Hosting: Since the address can change, it’s not suitable for hosting a website or game server, as external users won’t have a consistent address to connect to.

🗿 Static IP Address

A Static IP address is an address that is manually assigned to a device and remains fixed. It does not change.

• How it Works: An administrator manually configures the network settings of a device with a specific IP address, which is then permanently reserved for that device.
• Common Use: Essential for any device that needs to be reliably accessible over the network. This includes servers (web, email, game), network printers, and security cameras. Businesses typically purchase static public IPs for their public-facing services.

✅ Benefits

• Reliable for Hosting: The constant address makes it ideal for hosting services, as DNS records can point to it reliably.
• Predictable Access: You always know the address of the device, which is crucial for remote access and network management.

❌ Drawbacks

• Manual Configuration: It requires manual setup and increases the risk of configuration errors.
• Higher Cost: ISPs in India usually charge a premium for a static public IP address because it is permanently allocated to a single customer.