Day 68 of 90 Days of DevOps Challenge: Understanding OSI & TCP/IP Models

On Day 67, I explored core Networking Fundamentals for DevOps, focusing on:

• IP Addressing: IPv4, IPv6, Static & Dynamic IPs

• Public vs Private IPs

• Loopback Address & MAC Address

This provided a strong foundation to delve deeper into network communication models, which are essential for understanding how data flows across networks. whether in cloud deployments, Kubernetes clusters, or CI/CD pipelines.

Today’s focus is on two of the most important networking models. Both models are essential for troubleshooting, architecting networks, and understanding how systems talk to each other.

• The OSI Model

• The TCP/IP Model

OSI Model (Open Systems Interconnection)

The OSI Model is a 7-layer architecture that standardizes the transmission of data over a network. It breaks down network communication into manageable layers, helping us troubleshoot and design better systems.

• It’s a conceptual framework for network communication.

• Developed by ISO (International Organization for Standardization)

The 7 layers of the OSI Model are (Top to Bottom):

1. Application Layer:

   • This is the top layer responsible for interacting with end-user applications and providing services like web browsing, email, and file transfers.

   • Protocols like HTTP, FTP, SMTP, and DNS operate here.

2. Presentation Layer:

   • It handles data translation, encryption, and compression.

   • This layer ensures that data sent from the application layer of one system is readable by the application layer of another.

   • Protocols like SSL/TLS and formats like JPEG or GIF are examples.

3. Session Layer:

   • This layer is responsible for establishing, managing, and terminating sessions between applications.

   • It ensures continuous communication between devices.

   • Protocols such as NetBIOS and RPC work at this layer.

4. Transport Layer:

   • The transport layer ensures reliable data delivery with error correction and flow control.

   • Protocols like TCP provide reliable, ordered data transfer, while UDP offers faster, connectionless communication.

5. Network Layer:

   • Responsible for logical addressing and routing, this layer determines the best path for data to travel.

   • Protocols like IP and ICMP operate here.

6. Data Link Layer:

   • It manages node-to-node data transfer, MAC addressing, and error detection.

   • Ethernet is a common protocol at this layer, and switches operate here.

7. Physical Layer:

   • This layer deals with the physical medium of transmission, such as cables, switches, and electrical signals.

Understanding these layers helps in troubleshooting network issues effectively by isolating problems at specific layers.

TCP/IP Model

The TCP/IP Model (also called the Internet Protocol Suite) is the practical model used in real-world networking, especially in the design and functioning of the Internet. It simplifies the networking process into four layers, compared to the OSI Model's seven.

• based on a practical implementation model of networking.

• Developed by DoD (U.S. Department of Defense)

The four layers of the TCP/IP Model are:

1. Application Layer:

   • This layer provides services for network applications such as web browsers and email clients.

   • Protocols like HTTP, FTP, SMTP, DNS, and SSH function at this level.

   • It combines the OSI model’s application, presentation, and session layers.

2. Transport Layer:

   • This layer is responsible for end-to-end communication and data integrity.

   • It uses TCP for reliable data transmission and UDP for faster, less reliable communication.

3. Internet Layer:

   • This layer handles logical addressing and routing across networks.

   • It uses protocols like IP for addressing, ICMP for diagnostics, and ARP for resolving addresses.

4. Network Access Layer:

   • This layer manages the physical transmission of data over network hardware like cables and wireless connections.

   • Technologies such as Ethernet and Wi-Fi operate here.

The TCP/IP model is more aligned with practical networking and forms the basis of internet communication.

OSI Model vs TCP/IP Model

Why DevOps Engineers Should Know This

• Troubleshooting: Helps pinpoint which network layer is causing an issue. for example, DNS failures relate to Layer 7, while routing issues occur at Layer 3.

• Cloud Networking: AWS VPCs, Subnets, and Route Tables correspond to Layer 3 (Network), while Security Groups and NACLs align with Layer 4 (Transport).

• Kubernetes & Docker Networking: Service discovery, port mapping, and container communication utilize principles across the Transport and Network layers.

• Security: Firewalls, NACLs, and Security Groups function at specific layers, controlling traffic flow and access at both Network and Transport layers.

Final Thoughts

Understanding the OSI and TCP/IP models is foundational for anyone working in DevOps, cloud, or infrastructure engineering. These models provide clarity on how data moves across networks and where various tools, protocols, and cloud components operate within that flow.

With this strong networking base, I’m excited to move forward and explore DHCP (Dynamic Host Configuration Protocol) and DNS (Domain Name System) in the next part of my journey. Both are critical for automated IP addressing and domain name resolution, which are essential in both on-premises and cloud environments like AWS.

Stay tuned as I dive deeper into how devices get IP addresses dynamically and how domain names are mapped to those IPs across the internet and internal networks.