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Networking Core Protocols

Shubham
Shubham
Cybersecurity Enthusiast

Introduction​

okay let me go through it straight forward

this room covers the core application-layer protocols the internet uses everyday: DNS, WHOIS, HTTP, FTP, SMTP/POP3/IMAP.
these protocols help resolve names, fetch web pages, transfer files, and send/receive emails.

lame language definition:
these are the official "languages" computers speak for websites, files, emails, and domain lookup

formal definition:
Core network protocols are standardized application-layer communication rules that define how data is requested, transferred, and interpreted across the internet, enabling services like DNS resolution, HTTP browsing, FTP file transfer, and email transmission.

DNS (Domain Name System)​

dns converts names → ip addresses.
your browser can't understand domain names, only numbers.

lame language definition:
dns is the internet’s phonebook

formal definition:
DNS is a hierarchical, distributed naming system that resolves human-readable domain names into IP addresses and provides additional record types like MX, CNAME, PTR, etc.

DNS Example​

nslookup example.com
Server: 8.8.8.8
Address: 8.8.8.8#53

Non-authoritative answer:
Name: example.com
Address: 93.184.216.34

browser now knows where to send HTTP request.

WHOIS​

whois gives info about who owns a domain, when it was registered, etc.

lame language definition:
whois is “who owns this address on the internet?”

formal definition:
WHOIS is a query/response protocol used to look up registration data for domain names and IP address blocks.

WHOIS Example​

whois example.com
Domain Name: EXAMPLE.COM
Creation Date: 1995-08-13
Registrar: ...
Registrant Organization: IANA

used in reconnaissance.

HTTP (Hypertext Transfer Protocol)​

http is how browsers fetch web pages, APIs, json, images, etc.

lame language definition:
http is “give me this webpage”

formal definition:
HTTP is an application-layer protocol defining how clients and servers request and deliver web resources, using methods like GET, POST, PUT, DELETE, etc.

HTTP Example​

GET / HTTP/1.1
Host: example.com
User-Agent: curl/7.79.1
Accept: /

HTTP/1.1 200 OK
Content-Type: text/html
<html>...</html> ```
FTP (File Transfer Protocol)

ftp is used to upload/download files between client and server.

lame language definition: ftp is a courier service for files.

formal definition: FTP is a standard network protocol for transferring files over a reliable TCP connection, usually using port 21 for control and additional ports for data.

FTP Example​

ftp example.com
Name: anonymous
Password: guest

ftp> ls
ftp> get secrets.txt
ftp> bye

Email Protocols (SMTP, POP3, IMAP)​

SMTP​

used for sending emails.

lame language definition: smtp sends your mail to the post office.

formal definition: SMTP is a protocol for transferring outgoing email between clients and mail servers, and between mail servers.

POP3​

used for retrieving emails, usually downloads + deletes.

lame language definition: pop3 pulls emails down to your device.

formal definition: POP3 is a simple email retrieval protocol where the client downloads messages from server and optionally deletes them from the mailbox.

IMAP​

used for retrieving emails but keeps them synced across devices.

lame language definition: imap keeps your emails on the server so all devices see same inbox.

formal definition: IMAP is an email protocol allowing clients to view, organize, and synchronize mail stored on the server without deleting it.

Email Example (POP3 via telnet)​

telnet mail.example.com 110
+OK POP3 server ready
USER student
+OK
PASS password123
+OK Logged in
LIST
+OK 2 messages
RETR 1
Subject: Welcome
From: admin@example.com
QUIT

Why These Protocols Matter​

dns → resolves names
whois → reveals domain ownership
http → loads websites
ftp → transfers files
smtp/pop/imap → email communication

lame language definition: without these, the internet would be a pile of raw IP addresses and bytes

formal definition: Core protocols make internet services usable by providing standardized mechanisms for name resolution, content delivery, file transfer, and email exchange. Conclusion

networking core protocols explain how websites load, how domains resolve, how files are transferred, and how emails flow across servers.

if you understand dns, whois, http, ftp, smtp/pop3/imap — you understand how humans communicate over the internet at protocol-level.

`

Networking Concepts

Shubham
Shubham
Cybersecurity Enthusiast

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. `