What is TCP/IP Model
The TCP/IP model serves as a framework for visualizing the organization and transmission of data across a network. This framework aids network engineers and security analysts in conceptualizing network processes and identifying disruptions or security risks.
Comprising four layers — the network access layer, internet layer, transport layer, and application layer — the TCP/IP model enables security experts to dissect attacks when troubleshooting network issues. By analyzing the involved processes during an incident, professionals can deduce which layer or layers were targeted in an attack.
The four layers of the TCP/IP model are as follows:
1. Network Access Layer: Also known as the data link layer, this segment manages the exchange of data frames within a single network. It pertains to the physical hardware responsible for network transmission. Devices like hubs, modems, cables, and wiring fall under this layer. The address resolution protocol (ARP) is a component of this layer, aiding IP in directing data packets by correlating IP addresses with MAC addresses on the same physical network.
2. Internet Layer: Sometimes referred to as the network layer, this layer ensures the delivery of data to a destination host, even if it resides on a different network. It determines the appropriate protocol for handling data packets. Key protocols at this layer include:
- Internet Protocol (IP): Responsible for forwarding data packets to the correct destination. It relies on the Transmission Control Protocol/User Datagram Protocol (TCP/UDP) for final delivery. IP packets facilitate communication between distinct networks, routing them from the sender to the receiver. TCP/UDP retransmits lost or corrupted data.
— Internet Control Message Protocol (ICMP): Shares error and status updates about data packets, aiding in error detection and network troubleshooting. It reports dropped or missing packets, connectivity issues, and packet redirection to other routers.
3. Transport Layer: This layer ensures the dependable transfer of data between two systems or networks. The transport protocols operating here are TCP and UDP.
- Transmission Control Protocol (TCP): Ensures reliable data transmission to the intended service. TCP’s header contains the port number of the destination service.
— User Datagram Protocol (UDP): Utilized by applications prioritizing speed over transmission reliability. Unlike TCP, UDP data is less meticulously tracked. It’s commonly used in real-time, performance-sensitive applications like video streaming due to its lack of network connection establishment.
4. Application Layer: Corresponding to the application, presentation, and session layers of the OSI model, the application layer in the TCP/IP model is responsible for initiating or responding to network requests. It defines accessible internet services and applications for users. Some prevalent protocols operating at this layer include:
Hypertext transfer protocol (HTTP)
Simple mail transfer protocol (SMTP)
Secure shell (SSH)
File transfer protocol (FTP)
Domain name system (DNS)
Application layer protocols rely on underlying layers to transfer the data across the network.
