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.
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