When we talk about how devices communicate across a network whether you're sending an email, streaming a movie, or browsing the web one model quietly makes it all happen: the TCP/IP model.
Developed long before the OSI reference model, TCP/IP (also known as the DARPA or DOD model) forms the backbone of today's internet. While the OSI model uses seven layers, TCP/IP simplifies things by using just four:
Application Layer (Process Layer)
Transport Layer (Host to Host Layer)
Internet Layer (Internetworking Layer)
Link Layer (Network Interface / Network Access Layer)
Why TCP/IP Has Only Four Layers
The TCP/IP model came directly from the TCP/IP protocol suite, a large collection of communication protocols that evolved through real world use. Unlike the theoretical OSI model, TCP/IP wasn't designed to be perfect on paper it was designed to work.
Because of this, several OSI layers are merged together in TCP/IP. For example:
OSI's Application, Presentation, and Session layers are combined into the Application Layer in TCP/IP.
OSI's Data Link and Physical layers are combined into the Link Layer.
This makes the model more practical and straightforward, especially for network engineers.
The Four Layers of the TCP/IP Model (With Examples)
Application Layer
This is the layer where users and applications interact with the network.
Common protocols:
HTTP/HTTPS : web browsing
SMTP/IMAP : email
FTP/SFTP : file transfer
DNS : domain name lookup
Example: When you type www.youtube.com into a browser, the request is handled at the Application Layer using HTTP/HTTPS.
Transport Layer
Responsible for end to end communication between two devices (host to host communication).
Key protocols:
TCP (Transmission Control Protocol) : reliable, connection oriented
UDP (User Datagram Protocol) : faster, connectionless
Example:
Watching a live sports stream uses UDP, because speed matters more than perfect accuracy.
Downloading a document uses TCP, since every bit must arrive correctly.
Internet Layer
This layer handles routing deciding how data moves from one network to another.
Main protocol:
IP (Internet Protocol)
Example: Routing your packet from your home router in New York to a remote server in London is handled at this layer using IP addresses.
Link Layer
This layer deals with hardware level communication, such as sending data from your device to your router.
Common technologies:
Ethernet
Wi-Fi
ARP (Address Resolution Protocol)
Example: Your laptop sending data to your WiFi router uses WiFi standards and ARP to map IP addresses to MAC addresses.
Strengths of the TCP/IP Suite
TCP/IP became popular because it is:
Platform independent : It works on Windows, Linux, macOS, and nearly every device.
Based on open standards : Anyone can implement or adapt it.
Flexible and scalable : It powers everything from small home networks to the global internet.
Weaknesses and Vulnerabilities of TCP/IP
Because TCP/IP was created in an era when security wasn't a priority, it comes with several vulnerabilities.
Common TCP/IP Attack Types
Buffer Overflow Attacks Attackers exploit poorly written network code to overwrite memory.
SYN Flood Attacks An attacker sends repeated fake connection requests to overwhelm a server.
Denial of Service (DoS) Attacks Flooding the network with traffic to make services unavailable.
Fragmentation Attacks Malformed packet fragments can crash or confuse systems.
Oversized Packet Attacks Sending huge packets to exploit buffer limits.
IP Spoofing Pretending to be another IP address to bypass filters or impersonate devices.
Man in the Middle (MitM) Attacks Intercepting communication between two systems.
Session Hijacking Taking over an existing authenticated connection.
Passive Attacks (Sniffing)
Even without actively attacking, an adversary can capture data packets on insecure networks using tools like Wireshark. Example: On an open public WiFi network, an attacker could intercept unencrypted data.
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