Networking Fundamentals —
IP Addressing & Services

Why Do We Need IP Addresses?

From Part 1, we know every NIC has a MAC address — great for identifying devices on a local network. But MAC addresses are not practical for global communication. There is no hierarchy; routers cannot use them to determine where a device is located globally.

Just like sending a letter requires Country → State → City → Street → House Number, networks need a hierarchical location system. That system is called an IP Address.

What is an IP Address?

IP stands for Internet Protocol. An IP address identifies where a device is located on a network — think of it as a home address, while the MAC address is an identity card.

IPv4

IPv4 (Internet Protocol Version 4) is the most widely deployed version of IP. It uses 32 bits, written as four octets (0–255) separated by dots.

Example: 192.168.1.10 → four sections, each called an octet, each ranging from 0 to 255.

IPv4 allows 2³² ≈ 4.3 billion addresses — a number that seemed enormous in the early days but has been exhausted by smartphones, laptops, tablets, and IoT devices.

Why Not IPv5?

IPv5 actually existed — it was assigned to the Internet Stream Protocol (ST-II), designed for audio streams, video streams, and real-time communications. It was never intended to replace IPv4 as the general Internet protocol, so IPv6 became the successor.

IPv6

IPv6 (Internet Protocol Version 6) was created specifically to solve IPv4 address exhaustion. It uses 128 bits — providing 2¹²⁸ addresses, an unimaginably large number sufficient for every device on Earth many times over.

Example: 2001:0db8:85a3::8a2e:0370:7334

Public IP Addresses

A Public IP Address is globally unique and reachable from anywhere on the Internet. They are assigned by ISPs (Internet Service Providers). Your home router uses one public IP to represent the entire home network to the outside world.

Private IP Addresses

Private IPs are used inside local networks and are not routable on the public Internet. They exist because if every device needed a public IP, IPv4 would have been exhausted far sooner. Millions of networks can reuse the same private ranges internally.

Static vs Dynamic IP Addresses

A static IP is configured manually and never changes — essential for servers, printers, routers, and cameras that must always be reachable at a predictable address. A dynamic IP is assigned automatically (via DHCP) and can change over time — used for phones, laptops, and home computers where flexibility matters more than predictability.

Subnet Mask

When a computer wants to communicate, it must first answer: is the destination on the same local network, or is it remote? The subnet mask answers this question.

A subnet mask divides an IP address into two parts: the Network Part (which network does this device belong to?) and the Host Part (which specific device within that network?).

Example: IP 192.168.1.10 with mask 255.255.255.0 means:

• ›Network Part: 192.168.1 (the first 24 bits, identified by 255.255.255)
• ›Host Part: .10 (the last 8 bits, identified by .0 in the mask)

Default Gateway

The Default Gateway is the network’s exit door — the device that handles traffic destined for outside your local network. Think of it like a highway entrance: you stay on local streets within your city, but to reach another city you use the highway. In networking, the gateway is that highway entrance.

When a computer determines (via subnet mask) that the destination is not local, it sends the packet to the Default Gateway, which then decides where to forward it next. The gateway is typically:

• ›Home Router — common in home networks
• ›Enterprise Router — used in business and campus networks
• ›Firewall Appliance — provides security and routing between networks

Gateway vs Bridge

Beginners often confuse these two. The key distinction: a bridge joins segments into one network; a gateway connects separate networks.

DHCP

DHCP stands for Dynamic Host Configuration Protocol. Every device that joins a network needs four things: IP Address, Subnet Mask, Default Gateway, and DNS Server. Without DHCP, every device must be configured manually. With DHCP, a server (usually your router) assigns all of this automatically.

DHCP uses the DORA process — four messages between client and server:

Hostname

Humans dislike remembering IP addresses. A hostname is a human-readable name assigned to a device — instead of remembering 192.168.1.50, you use SATWIK-LAPTOP. Hostnames make systems easier to identify in logs, configurations, and network tools.

Localhost

Localhost means this computer itself. When software communicates with localhost, it is communicating with services running on the same machine — no network traffic leaves the computer. This is essential for developers running local web servers, testing APIs, and database development without requiring a network connection.

127.0.0.1

127.0.0.1 is the special IPv4 loopback address — the actual IP that represents localhost. It always points back to the local machine and allows software to test and run without touching the network at all.

Introduction to DNS

Imagine typing 142.250.193.14 instead of google.com every time. DNS (Domain Name System) solves this.

DNS converts human-readable domain names into IP addresses that computers use — exactly like your phone’s contacts book converts "Mom" into a phone number. You remember the name; the system looks up the number.

Part 2 Summary