SUBNET, OSI Model

Subnet

Breaking IP address into smaller chunks, easier to manage. A section of a network address.

A subnet (short for subnetwork) is a smaller part of a larger network.

And yes — it is defined by taking a section of the network address and dividing it into smaller parts.

Network Address

192.168.1.0 is called a network because it represents a group of IP addresses that belong together in the same local area network. It’s the identifier for that subnet.

Analogy:

Imagine an apartment building:

• The building address is like 192.168.1.0 → that’s the whole network

• The apartments inside are like 192.168.1.1, .2, .3, up to .254 → those are the devices

CIDR

determines how big ro small the network is. same as subnet mask

Subnet Mask

A subnet mask is a number that tells the computer which part of an IP address is the network and which part is the host (device).

It helps the system separate:

• 🌐 The network portion (where the device belongs)

• 💻 The host portion (which specific device it is)

A subnet mask tells a device how many addresses are in its network, and helps it figure out who it can talk to directly.

OSI Model (Open system Interconnection Model)

each part of the 7 layer describes different types of connectivities. each art of the layer 7 is responsible for how data or information is transferred between devices. Like a team where each player as a specific role

OSI (Physical Layer)

All about cables and hardware and how data is transfered through wires or wirelessly. Information will not be ableto more between devices without this layer.

OSI (Data Link)

make sure data moves between devices smoothly

he Data Link Layer makes sure that data is sent from one device to another on the same network using MAC addresses, frames, and error checks. It helps the data move smoothly and correctly between nearby devices.

Network Layer

Network layer: "Works like aGps"r, "Oh So where is my data going? "

-Assigns an IP Address to the data and determines the best route through the network, making sure it goes to the right destination

Transport Layer

· Transport layer: Delivery truck

=> "all the pieces of data arrive in the right order and

groups them together correctl y If any piece is

missing, it sends it again. "

Network vs Data link

Layer 2 vs Layer 3 – Simple Side-by-Side

Feature	Layer 2: Data Link	Layer 3: Network
📦 Purpose	Move data between devices on the same network (LAN)	Move data between networks (WAN/internet)
🆔 Uses What Address?	MAC address (physical/hardware address)	IP address (logical/software address)
🧱 Unit of Data	Frame	Packet
🎯 Focuses On	Local delivery (device-to-device nearby)	Global routing (device-to-device across networks)
⚠ Error Handling	Basic error checking (like CRC)	Chooses best path, no direct error correction
🔌 Device Example	Switch	Router
🧑‍🤝‍🧑 Who Uses It?	Computers, switches inside a LAN	Routers, firewalls, internet gateways

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Session Layer

"Opens and closes connection between devices. Closes connection when the Communication is finished

Presentation

"translates data into a format both devices understand and encryts data for security. Example: Converting and locking your message before it sends

Application

"The one you directly interact with. Where you access websites,-mail, messaging apps. DATA Becomes useful to you!

what is the difference between getting data to the right device and getting into the right network? aarent they both the same? the data is going to a device anyways? (Network vs DATA LINK)

• The Network Layer is responsible for using IP addresses to find the location where the data needs to go.

• This means the data can travel through routers, cities, and even countries.

• Example: Your computer sends a request to Google — the IP address helps route it through the internet.

• Each home, business, or school has its own private network (like 192.168.x.x).

• The IP address guides the data to the right destination network, like finding the correct building or company.

• Once the data reaches the local network, it still needs to find the exact device (like your phone, PC, or printer).

• That’s where the MAC address comes in — it identifies each unique device.

• This happens inside the same building or LAN.