Virtual Cloud Networks (VCNs) Explained

Key Concepts

Virtual Cloud Networks (VCNs) in Oracle Cloud Infrastructure (OCI) are a foundational component for networking. Understanding VCNs involves grasping the following key concepts:

• Subnets
• Route Tables
• Security Lists
• Internet Gateway

Subnets

Subnets are segments of a VCN that can contain resources like compute instances. Subnets can be public or private, depending on whether they are accessible from the internet. Public subnets are typically used for resources that need to be accessed externally, while private subnets are used for internal resources.

Example: If you are deploying a web server that needs to be accessible from the internet, you would place it in a public subnet. Conversely, if you are running a database server that should only be accessible internally, you would place it in a private subnet.

Route Tables

Route tables define the traffic routes for subnets. Each route table contains rules (routes) that specify where network traffic should be directed. Route tables are essential for managing traffic flow within and outside the VCN.

Example: Suppose you have a public subnet with an internet gateway. You would configure a route table to direct all internet-bound traffic (0.0.0.0/0) to the internet gateway, ensuring that resources in the public subnet can communicate with the internet.

Security Lists

Security lists act as virtual firewalls for subnets, controlling inbound and outbound traffic. Each security list contains rules that specify which traffic is allowed or denied. Security lists provide fine-grained control over network security.

Example: If you want to allow HTTP traffic (port 80) to your web server but block all other inbound traffic, you would create a security list with an allow rule for port 80 and a deny rule for all other ports.

Internet Gateway

An internet gateway allows resources in a public subnet to communicate with the internet. It acts as a bridge between the VCN and the public internet, enabling outbound and inbound traffic.

Example: If you have a web server in a public subnet that needs to be accessible from the internet, you would attach an internet gateway to the VCN and configure the route table to direct internet-bound traffic to the gateway.

Conclusion

Understanding Virtual Cloud Networks (VCNs) in OCI involves knowing how to create and manage subnets, route tables, security lists, and internet gateways. By mastering these concepts, you can design secure, scalable, and efficient network architectures to support your cloud-based applications.