How HTTP Works Across TCP/IP Layers

This page explains how HTTP requests flow through the different layers of the TCP/IP protocol stack. When you make a request from a web browser or application, the data travels through multiple network layers—each with a specific role—before reaching the destination server. Understanding this layered approach is fundamental to grasping how modern networking and web communication work.

1. Application Layer (HTTP)

The application (e.g., a web app) creates an HTTP request such as GET /data HTTP/1.1.
Headers like Host and User-Agent are added.
The request is passed to the Transport Layer for delivery.
The application does not handle IPs or connections directly; it relies on TCP.

2. Transport Layer (TCP)

TCP segments the HTTP request into smaller pieces called segments.
It assigns a source port (random) and a destination port (80 for HTTP, 443 for HTTPS).
A 3-way handshake establishes the connection:
1. SYN: Client → Server (connection request)
2. SYN-ACK: Server → Client (acknowledge + request)
3. ACK: Client → Server (connection established)
TCP ensures data reliability, ordering, and error recovery.

3. Internet Layer (IP)

TCP segments are encapsulated into IP packets.
Each packet contains a source IP (Server A) and destination IP (Server B).
Routers use the IP addresses to forward packets to the destination.
IP is best-effort (unreliable) — reliability is handled by TCP.

4. Network Access / Link Layer (Ethernet, Wi-Fi)

IP packets are wrapped in frames (like Ethernet frames).
Each frame includes the MAC address of the next hop (switch or router) and a checksum.
The frame is transmitted as electrical/optical/radio signals.
At each hop, the MAC layer checks and forwards the frame to the next hop.

Where the Connection is Established

The connection is established at the Transport Layer (TCP), not at the Application or Link Layer.
After the 3-way handshake, a logical connection is established between:
- Client IP + Port ↔ Server IP + Port
This connection is virtual — no dedicated physical wire exists between the two systems.

Will the Same Connection Be Used for All Requests?

HTTP/1.0

Each HTTP request opens a new TCP connection and closes it after the response.

HTTP/1.1

Introduced persistent connections (Connection: keep-alive).
Multiple requests can reuse one TCP connection.

HTTP/2

Uses a single TCP connection to send multiple requests concurrently (multiplexing).

Summary of the Flow

HTTP request is generated by the application.
TCP creates a reliable connection via handshake.
IP routes the packets through routers to the destination server.
Ethernet/Wi-Fi transmits frames physically across the network.
The receiving server unwraps the layers and processes the HTTP request.

Diagram Example

The diagram below illustrates how multiple HTTP requests can either reuse a single TCP connection (HTTP/1.1, HTTP/2) or use multiple separate TCP connections (HTTP/1.0).