Networking basics: client and server, IP address, IPv4 counting, static and dynamic IP, gateway

By Ravindra Bagale, trainer · LinkedIn · Last updated: 7 October 2026

1. Why we practise on a cloud server, not VirtualBox

Why. This is an AWS course. In a company you will not work on your own laptop; you will work on servers that sit far away in a data center. So from day one we practise the way the job is done.

What. Almost everyone in class has a Windows laptop. To learn Linux and AWS you have two options:

1. Option 1: install VirtualBox on your laptop and run Linux inside it.
2. Option 2: create an AWS account and launch a Linux server in the cloud, using the AWS Free Tier offer for new accounts (check what the current offer includes when you sign up).

How we choose. We take Option 2, because "we are cloud and server people". Your laptop only becomes the screen and keyboard; the real work happens on a server in AWS.

2. Why networking comes before Linux

Why. The server you launch in AWS is not in front of you. To reach it from your laptop you go over the internet. If you don't know what an IP address is, or how a request finds a server, you will be stuck at the very first connection.

What. So we spend the first 2 to 3 days on networking basics, and only then start Linux.

How it helps later.

1. You launch a server in AWS.
2. AWS gives that server an IP address.
3. Your laptop uses that IP to connect to the server.
4. After that, every Linux command you type runs on that far-away server.

3. Client and server: Instagram request and response

Why. Every app you use works the same way. Once you see one example clearly, you understand all of them.

What. Suppose I open the Instagram app on my mobile.

1. My phone sends a request to Instagram's server: "show me reels".
2. The server checks its database.
3. The server fetches the reels from the database.
4. The server sends a response back to my phone.
5. The reels play on my screen.

Same pattern, different apps.

Where do these servers run? A company can run its servers in its own data centers or rent them from a cloud provider such as AWS, Microsoft Azure or Google Cloud (GCP). Some companies spread their app across more than one provider, so if one provider has an outage, the app keeps working from the others. This is called multi-cloud. AWS started in 2006, the earliest of these three, which is one reason it has so much experience. As listed on AWS's global infrastructure page at the time of writing, the AWS Cloud spans 124 Availability Zones in 39 Regions.

4. Why every machine needs an IP address

Why. My phone has to send the request somewhere. On the internet, "somewhere" means an address. Humans have names, and we recognise people by their names. In the same way, machines on the internet are recognised by their IP address.

What. An IP address is a number given to a machine on a network so that other machines can send data to it.

How the app finds the server's IP. The Instagram app does not keep the server's IP written inside it. It keeps a domain name (a name like api.example.com). When the app needs the server, the phone asks DNS (Domain Name System), "what is the IP of this name?", and DNS answers with the IP. Then the phone sends the request to that IP.

1. The app knows the name, for example api.example.com.
2. The phone asks DNS for the IP of that name.
3. DNS replies, for example 7.7.7.7.
4. The phone sends the request to 7.7.7.7.

5. IPv4 and IPv6

Why two kinds? IPv4 was the first version used on the internet, and it is running out of addresses (you will see the exact numbers below). IPv6 was made to solve that.

What.

How we learn it. IPv4 is still used everywhere and it is easier to read, so we learn IPv4 first. IPv6 will come later.

6. IPv4: four parts, each from 0 to 255

Why. You must be able to look at a number and say immediately, "this is an IP address" or "this is not".

What. An IPv4 address has 4 parts separated by dots: _ . _ . _ . _. Each part can be any number from 0 to 255. Nothing bigger.

• Lowest possible: 0.0.0.0
• Highest possible: 255.255.255.255

How to check. Worked examples:

Not every number in this range can be used on the internet. Some ranges are kept for special jobs: for example 127.0.0.1 always means "this same machine", and ranges like 192.168.x.x are kept for home and office networks. We will see these in detail later.

7. Counting IPs: what comes after 0.0.0.255?

Why. When AWS gives you a network, you will need to know how many IPs are inside it. That starts with simple counting.

What. Count only the last part first:

1. 0.0.0.0
2. 0.0.0.1
3. 0.0.0.2
4. … keep going …
5. 0.0.0.255

From 0 to 255 is 256 IPs.

So what is the next IP after 0.0.0.255? In class, a student said 0.0.1.256. That is wrong, because 256 is bigger than 255.

How the rule works (like a car's odometer):

1. When a part reaches 255 and you add 1, that part becomes 0.
2. The part on its left goes up by 1.
3. If that left part was also 255, it also becomes 0 and the next left part goes up by 1.

Worked examples:

You keep counting like this until the very last IP, 255.255.255.255.

8. How many IPv4 addresses are there in total?

Why. This number explains why the world is running out of IPv4.

What and how, step by step on the board:

1. Last part only: 0.0.0.0 to 0.0.0.255 = 256 IPs.
2. Last two parts: when the third part is 0, the fourth part gives 256 IPs. When the third part is 1, another 256. … When the third part is 255, another 256. So 256 × 256 = 65,536 IPs.
3. Last three parts: 256 × 256 × 256 = 16,777,216 IPs.
4. All four parts: 256 × 256 × 256 × 256 = 4,294,967,296 IPs.

In Indian numbering, 4,294,967,296 is written 429,49,67,296, about 429 crore IPv4 addresses.

9. Why IPv4 is running short

Why it matters. If there are not enough addresses, new phones and servers cannot each get their own public IP. This is why tricks like dynamic IP and sharing one IP exist.

What uses IPs. It is not one IP per person. One person can need many:

1. A phone with two SIMs.
2. A laptop and a tablet.
3. A smart TV.
4. The GPS in a car, and the Android player on a car dashboard.
5. Sensors and other IoT devices.
6. And every server of every company.

So 429 crore is far too few. And remember, some of those 429 crore are reserved for special jobs and can never be used on the internet.

10. Static IP and dynamic IP

Why. Because IPs are few, they cannot all be given away permanently. Most devices get an IP only while they are online, and only some get a fixed one.

What. An IP address is just a number. Whether it is static or dynamic depends on how it is given to the device:

11. Dynamic IP: mobile data on and off

Why. This is how a few crore IPs are shared among many more devices.

What. Suppose I have a Jio SIM.

1. I turn on mobile data. Only now does my phone get an IP, say 3.3.3.3.
2. I use WhatsApp for 30 minutes. The IP stays with my phone.
3. I turn off mobile data (or switch on airplane mode, switch off the phone, or lose network).
4. 3.3.3.3 is released and goes back to the pool.
5. The network gives 3.3.3.3 to someone else who just turned on data.
6. When I turn data on again, I may get a different IP, say 5.5.5.5.

Where does that IP go at night? Not to the other side of the world. Each mobile company owns its own blocks of IPs (given through the regional registry, APNIC for India), so Jio's IPs are used only by Jio's own users.

1. You switch off mobile data at night.
2. Your IP goes back into Jio's pool of free IPs.
3. Another Jio user who switches data on (maybe a night-shift worker, or someone waking up early) gets that IP.
4. In the morning you switch data on and get whichever free IP Jio has at that moment, often a different one.

One more real-life point. Mobile companies also save IPs another way: they often give phones a private address and let many phones share one public IP (this is called carrier-grade NAT). On the board we keep 3.3.3.3 to keep the idea simple; the idea of reuse is the same.

12. Static IP: it stays

Why. Some machines must be found at the same address every time, even after a restart. That is a server's job.

What. A static IP, say 7.7.7.7, stays with the device even when it is switched off.

How you get one.

1. Ask your internet provider (Jio, Airtel, Vi and others) for a static IP.
2. Give a reason, such as running a server.
3. It costs extra, which is why not everyone takes one.
4. In AWS, the static IP is called an Elastic IP. You allocate it to your account and attach it to your server.

13. Client and server: who is who?

Why. Every network diagram has clients and servers. You must know which side is which.

What.

1. The server is the big box that answers, for example Instagram's server.
2. The clients are everyone who asks: the Android app, the iPhone app, a browser on a laptop, an iPad, even a car screen.
3. Clients usually have dynamic IPs.
4. Servers usually have static IPs.

14. Why a server needs a fixed IP: the 1 crore users story

Why. Clients can change their IP every day and nothing breaks. If a server changes its IP, lakhs of people are affected.

What happens. Suppose Instagram's server was on a dynamic IP 3.3.3.3, used by 1 crore users:

1. The DNS record for the app's domain name says: the server is at 3.3.3.3.
2. 1 crore phones have asked DNS and remember (cache) the answer 3.3.3.3 for some time.
3. The server restarts for maintenance and, being dynamic, comes back with a new IP, 5.5.5.5.
4. Phones still send requests to 3.3.3.3. Nothing is there now. For those users, the app is down.
5. Someone must update the DNS record to 5.5.5.5, and users keep hitting the dead address until their cached answers expire.
6. Firewall rules and partner systems that allowed 3.3.3.3 also break and must be changed.
7. This would happen again after every restart.

How it is solved. Give the server a fixed IP. Then a restart changes nothing: DNS still points to the right place, and firewall rules keep working. In AWS, the normal public IP of a server can change when you stop and start it, so for a server you attach an Elastic IP, which stays the same until you release it.

Student question: "IP kami ahet, mhanje kadhitari kai problem yeil na?" (IPs are few, so won't there be a problem some day?)

Yes, that is why static IPs are not free for life:

1. A static IP from an internet provider is given for a period.
2. If the period ends or it is not paid, it goes back to the pool.
3. In AWS, if you release an Elastic IP, it goes back to AWS's pool, and you usually cannot get the same one back.

15. Gateway IP: how does my phone reach the server?

Why. A student asked: "Client cha IP assign jhalela ahe, ani server sathi pan ahe, mag te connect kasa hotat?" (The client has an IP and the server also has one, so how do they actually connect?) The answer is the gateway.

What. A gateway is the door out of your network. Every packet that has to go outside your network goes to the gateway first.

Example on the board. I am in Pune, in Shivaji Nagar, on Jio.

1. I turn on mobile data.
2. My phone gets its IP, 3.3.3.3.
3. My phone also gets a gateway IP, 3.3.3.1. This is the address of the Jio tower's side of the network.
4. Everything my phone sends to the internet goes first to 3.3.3.1.

16. Snapchat "Hi": the packet's journey, hop by hop

Why. Now we put everything together: client IP, server IP, DNS and the gateway.

What is a packet? Data on the internet travels in small pieces called packets. Each packet carries:

The gateway IP is not written inside the packet. The packet is only sent to the gateway.

How "Hi" reaches the server. Suppose Snapchat's server is in an AWS data center in Mumbai with IP 8.7.7.7 (this is only a "suppose" example to learn with; all IPs on this board are dummy numbers).

1. I type "Hi" in Snapchat on my Jio phone in Pune.
2. The app knows the server's name. The phone asks DNS for its IP and gets 8.7.7.7.
3. The phone makes a packet: To 8.7.7.7, From 3.3.3.3, Data "Hi".
4. The phone sends the packet to its gateway, 3.3.3.1 (the tower).
5. The gateway router reads the To IP, 8.7.7.7, and sends the packet to the next router on the way, for example 4.4.4.1.
6. That router does the same: reads the To IP and sends it one step closer.
7. Hop by hop, the packet reaches the network that owns 8.7.7.7, and then the Snapchat server.
8. The reply comes back the same way, now with To 3.3.3.3 and From 8.7.7.7.

17. How do the routers know which way to send it?

Why. The tower has never heard of your message. How does it know which direction Mumbai is?

What. Two different things are working here:

1. DNS is used by the phone, not by the towers. A company buys its domain name from a registrar (for example GoDaddy) and adds a DNS record that says "this name is at this IP". Your phone uses DNS to turn the name into an IP, like 8.7.7.7.
2. Routers forward using routes. Every network on the internet (Jio, AWS, and others) announces which IP ranges it owns. This announcing is done with a protocol called BGP. Every router builds a table from these announcements: "for this range, send it that way".
3. So the tower does not need to know Snapchat. It only needs to know "8.7.7.7 is in a range owned by that network; send it to the next hop that way".

18. Your home WiFi router is your gateway

Why. You can't log into a Jio tower, but you can log into the small box at home. It does the same job, so it is the best place to see a gateway with your own eyes.

What. At home, the WiFi router is the gateway for all your devices:

1. All home devices send their packets to the router, 192.168.0.1.
2. These 192.168.x.x addresses are private; they work only inside your home.
3. The router has one public IP from your internet provider, and it sends everything on to the provider's gateway.
4. Your phones still reach the internet: the router swaps their private IP for its public IP on the way out (this is called NAT) and swaps it back on the way in.

Some routers use 192.168.1.1 instead of 192.168.0.1. Never use the .0 address for a device or for logging in.

19. Homework: log into your home router

Recap

Samjla ka? Tonight, log into your router and bring the three IPs. In the next class we go deeper into IPs.

Ravindra Bagale, trainer: linkedin.com/in/ravindra-bagale. All IPs on the board are dummy numbers for learning. Snapchat in AWS Mumbai is a "suppose" example, not a fact about Snapchat.