Concepts: Networks, IP, DNS, Packets

What Is a Network?

A network is any group of devices that are connected so they can share data. Your phone, your router at home, and your ISP’s equipment are all part of a network. The internet is just a very large network of networks — millions of them, all connected and talking to each other using agreed-upon rules.

When you log into your bank’s website and transfer money, your browser is sending data to the bank’s server. That data travels through your Wi-Fi or mobile connection, through cables, through data centres, and back again — all in under two seconds.

IP Addresses — The Postal Address of the Internet

Every device that connects to the internet needs an address so data knows where to go. This is called an IP address (Internet Protocol address).

Think of it this way: your home has a postal address. Without it, no parcel can find you. Every device on the internet has an IP address. Without it, no data packet can find you.

IP addresses look like this: 142.250.192.46. Four numbers separated by dots, each between 0 and 255. That particular address belongs to Google.

Public vs. Private IP

Your router has a public IP address — this is the address the rest of the internet sees. All the devices in your home (your phone, laptop, smart TV) share this one public IP.

Inside your home network, each device gets a private IP address — something like 192.168.1.5. Your router keeps track of which private device gets which data from the outside world.

Internet ← Public IP: 103.21.58.10 → Your Router → Private IPs:
                                                      Phone: 192.168.1.2
                                                      Laptop: 192.168.1.3
                                                      Smart TV: 192.168.1.4

DNS — The Internet’s Phone Book

When you type sbi.co.in into your browser, your computer does not know where that is. It only knows addresses — numbers like 203.197.166.60. So how does it find SBI’s server?

This is where DNS (Domain Name System) comes in.

Imagine you know someone as “Priya from Haldwani.” You don’t know her phone number. But you have a phone book that can look up “Priya from Haldwani” and return her number. DNS is exactly that phone book — except it converts domain names into IP addresses, and it works in milliseconds.

How a DNS lookup works, step by step:

1. You type sbi.co.in into your browser
2. Your phone checks its own memory first — “Have I looked this up recently?” (This is called the DNS cache)
3. If not, it asks your ISP’s DNS server: “What is the IP for sbi.co.in?”
4. The ISP’s DNS server may ask other DNS servers higher up the chain
5. Eventually the answer comes back: 203.197.166.60
6. Your browser now connects to that IP address

The whole process takes milliseconds. You never see it happen.

Packets — Breaking Data into Pieces

Here is something surprising: when you send a WhatsApp photo to a friend, that photo does not travel as a single chunk. It gets broken into hundreds or thousands of small pieces called packets.

Why? Because the internet was designed for resilience. If one route is congested, individual packets can take different paths. If one packet gets lost, only that piece needs to be resent — not the whole photo. This is much more efficient than sending one giant chunk that would need to be completely re-sent if anything went wrong.

Pandey sir’s postal analogy: Imagine writing a very long letter — 20 pages. You could put it in one giant envelope and hope it arrives. Or you could number each page, put each in its own envelope addressed to the same destination, and send them separately. Some might go through Lucknow, some through Delhi. All arrive at the destination and are reassembled in order.

Each packet contains:

• A piece of the actual data (the “payload”)
• The destination IP address
• The source IP address
• A sequence number (so packets can be reassembled in order)
• Error-checking information

Routing — Finding the Path

Once data is broken into packets, each packet needs to find its way across the internet. This is done by routers — devices whose entire job is to receive packets and decide where to send them next.

Imagine a packet travelling from your phone in Bhopal to a server in Mumbai. It might pass through:

Your phone → Mobile tower → ISP network → City router →
Backbone router → Maharashtra network → Mumbai data centre

Each router along the way looks at the destination IP address and makes a decision: “Which direction should I send this next?” This is called routing, and there are sophisticated algorithms that make these decisions in microseconds, accounting for congestion and failures on the network.

Protocols — The Agreed Rules

None of this works unless every device agrees on the same rules. These rules are called protocols.

• IP (Internet Protocol) — how packets are addressed and routed
• TCP — how reliable delivery is guaranteed
• HTTP — how browsers and web servers communicate
• HTTPS — encrypted HTTP (the padlock you see in the browser)

Think of protocols like railway track gauge — all trains in India are built to the same track width. Different manufacturers, different trains, but they all run on the same tracks. Protocols are the agreed-upon “gauge” of the internet.

Putting It Together: The Online Banking Journey

Now you can answer the opening question. When you log into your bank’s website and transfer money:

1. Your browser creates a request (using HTTPS protocol)
2. DNS resolves onlinesbi.sbi to an IP address
3. The request is broken into TCP/IP packets
4. Packets are routed hop by hop from your device through your network to the bank’s servers
5. The bank’s servers verify your identity and process the transfer instruction
6. A response travels back the same way — broken into packets, routed, reassembled
7. Your screen shows “Transfer Successful” in under two seconds

Every single step in that chain used the concepts from this session.