OCI Networking Explained: Virtual Cloud Networks (VCN) Deep Dive

When I started learning networking in Oracle Cloud Infrastructure, one thing became obvious very quickly: If IAM controls who can access resources, networking controls how everything communicates. In this article, I’m breaking down Virtual Cloud Networks (VCN) properly. Not just definitions, but how it actually works underneath. 🧠 Part 1: CIDR Blocks and IP Notation (The Foundation) Before we touch VCNs, we need to understand CIDR. What is CIDR? CIDR stands for Classless Inter-Domain Routing. Format: A.B.C.D/x Example: 10.0.0.0/16 /x = network portion Remaining bits = host portion An IPv4 address has: 4 octets 8 bits each 32 bits total The Rule of Size The smaller the prefix, the larger the network. Formula to calculate total IP addresses: 2^(32 - x) Example: For 10.0.0.0/16 2^(32 - 16) = 2^16 = 65,536 IP addresses Binary Conversion Each octet is based on powers of 2: | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 | Example: 192.168.0.2 in binary: 11000000.10101000.00000000.00000010 You don’t ne