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Networking Concepts

OSI Model​

okay let me go through it straight forward

so networking has this 7 layer model called OSI model
it’s basically a structured way to understand “how data moves” from your device to another device

lame language definition:
it is a 7-step pipeline through which data passes. each layer has a job, adds some info, and sends it to the next one

formal definition:
the OSI model (Open Systems Interconnection) standardizes communication functions into 7 abstraction layers to ensure different systems can communicate reliably

the 7 layers (in simple and useful language)​

Layer 7 — Application
the apps you actually use (browser, ssh, discord)

Layer 6 — Presentation
formats and translates data (encryption, compression, encoding)

Layer 5 — Session
creates and maintains the connection (opening, closing, maintaining sessions)

Layer 4 — Transport
splits data into segments, handles ports, and ensures delivery (tcp/udp)

Layer 3 — Network
handles IP addresses and routing (deciding the best path)

Layer 2 — Data Link
mac addressing, local network delivery, error detection

Layer 1 — Physical
actual electrical/optical signals, cables, wifi waves

basically:
7 → what users see
1 → how bits physically travel

TCP/IP Model​

it’s like OSI but the one that the internet actually uses.
more practical, fewer layers.

lame language definition:
TCP/IP is OSI model but compressed into 4 layers so engineers don’t cry

formal definition:
TCP/IP (Transmission Control Protocol / Internet Protocol) is a suite of communication protocols used to interconnect network devices on the internet

layers​

Application Layer
combines OSI’s layers 5,6,7
your apps, formats, protocols like http, dns, ftp

Transport Layer
manages port numbers + segmentation + reliability
(TCP/UDP live here)

Internet Layer
IP addressing + routing

Network Access Layer
equals OSI layer 1+2
MAC, frames, physical transmission

IP Addresses & Subnets​

ip = internet address of a device
A.B.C.D basically

now every IP address has two parts:

Network part → which network you belong to
Host part → your unique device inside that network

so how do we know which part is which?
using subnet mask

lame language definition:
subnet mask draws a line between “network” and “host” portion of the IP address

formal definition:
a subnet mask is a 32-bit number that divides an IP address into network and host identifiers

example:
255.255.255.0 → first 3 octets = network, last = host

so valid hosts become .1 to .254

TCP and UDP​

TCP​

the reliable guy
does handshake, ensures packet delivery, checks order
it’s slow but trustworthy

use cases: https, ssh, ftp, email

UDP​

the fast guy
no handshake, no guarantee, no ordering
works when speed matters

use cases: video calls, gaming, streaming

lame language definition:
TCP cares, UDP doesn’t

Encapsulation​

when data moves through layers, each layer wraps it with its own piece of information
like putting a gift into multiple wrapping papers

formal definition:
encapsulation is the process where each networking layer adds its own header (and sometimes trailer) to the data from the layer above

example flow:
application data → transport segment → IP packet → frame → bits

receiver does the reverse (decapsulation)

Telnet​

telnet is an old protocol to remotely access systems

lame language definition:
it is SSH but without encryption … like shouting your password in public

formal definition:
telnet is an application protocol used to provide a bidirectional text-based communication using a virtual terminal connection over TCP (typically port 23)

not used anymore because everything is plaintext, so attackers can sniff credentials easily

Conclusion​

all networking concepts here boil down to one idea:

data doesn’t just travel; it passes through layers, gets wrapped with info, uses protocols to move, and gets delivered safely using IP + TCP/UDP.

this is the backbone of how the internet works. <!-- truncate -->