Application Layer

How Does DNS Work?

DNS (Domain Name System) is the internet’s phonebook: it translates human-readable domain names like example.com into the IP addresses machines use to connect,…

Difference Between HTTP and HTTPS

HTTP (HyperText Transfer Protocol) transfers web data in plain text, while HTTPS is the same protocol running over a TLS-encrypted connection — so HTTPS adds e…

What is a Proxy Server?

A proxy server is an intermediary that sits between a client and the destination server, forwarding requests and responses on the client’s behalf while optiona…

TCP/IP Model vs OSI Model

The OSI model is a seven-layer conceptual reference used for teaching and troubleshooting, while the TCP/IP model is a four-layer practical model that actually…

HTTP/2 vs HTTP/1.1: What Changed?

HTTP/2 replaces HTTP/1.1’s text-based, one-request-per-connection model with a binary framing layer that multiplexes many requests and responses over a single…

What is the HTTP Request Lifecycle?

The HTTP request lifecycle is the full sequence a browser follows to load a resource: DNS resolution, TCP (and TLS) connection setup, sending the HTTP request,…

What is the Application Layer (OSI Layer 7)?

The Application Layer (Layer 7, the topmost OSI layer) is where network-aware software directly interacts with the user or another program, providing the proto…

What is SNMP (Simple Network Management Protocol)?

SNMP (Simple Network Management Protocol) is an Application-layer protocol used to monitor and manage network devices — routers, switches, servers, printers —…

What is FTP (File Transfer Protocol)?

FTP (File Transfer Protocol) is an application-layer protocol for transferring files between a client and a server over a network, using a separate control con…

What is SFTP (SSH File Transfer Protocol)?

SFTP (SSH File Transfer Protocol) is a secure file transfer protocol that runs entirely over a single encrypted SSH connection on port 22, providing file opera…

What is SMTP (Simple Mail Transfer Protocol)?

SMTP (Simple Mail Transfer Protocol) is the application-layer protocol used to send and relay email between mail servers, and from a mail client to its outgoin…

What is IMAP (Internet Message Access Protocol)?

IMAP (Internet Message Access Protocol) is an application-layer protocol that lets an email client read and manage messages that remain stored on the mail serv…

What is POP3 (Post Office Protocol version 3)?

POP3 (Post Office Protocol version 3) is an application-layer protocol for retrieving email that traditionally downloads messages from the mail server to a sin…

What is Telnet?

Telnet is an application-layer protocol that provides a text-based, interactive terminal session to a remote host over TCP port 23, sending everything — includ…

What is SSH (Secure Shell)?

SSH (Secure Shell) is an encrypted application-layer protocol, typically running on TCP port 22, that provides secure remote login, command execution, and file…

What is NTP (Network Time Protocol)?

NTP (Network Time Protocol) is an application-layer protocol, running over UDP port 123, that synchronizes a device’s clock to an accurate reference time by ex…

What is LDAP (Lightweight Directory Access Protocol)?

LDAP (Lightweight Directory Access Protocol) is an application-layer protocol, typically running on TCP port 389 (or 636 for LDAPS), used to query and modify h…

What Is HTTP/3 and QUIC?

HTTP/3 is the third major version of HTTP that runs over QUIC, a transport protocol built on UDP, instead of TCP — this eliminates TCP-level head-of-line block…

HTTP Methods Explained (GET, POST, PUT, PATCH, DELETE)

HTTP methods define the intended action on a resource: GET retrieves data safely without side effects, POST creates a resource or triggers processing, PUT repl…

HTTP Status Codes Explained in Detail

HTTP status codes are three-digit responses that classify the outcome of a request into five families — 1xx informational, 2xx success, 3xx redirection, 4xx cl…

HTTP Headers Explained: Key Types and Uses

HTTP headers are key-value metadata sent alongside a request or response that control behavior without touching the body — covering content negotiation (Accept…

What is HTTP Keep-Alive?

HTTP Keep-Alive is a mechanism that reuses a single TCP connection for multiple HTTP requests and responses instead of opening a new connection for every reque…

What is Chunked Transfer Encoding?

Chunked transfer encoding is an HTTP/1.1 mechanism that lets a server stream a response body in a series of independently-sized chunks without knowing the tota…

What is HTTP Content Negotiation?

HTTP content negotiation is the process by which a client and server agree on the best representation of a resource to return — such as its format, language, o…