What is RFC1918 (Private IP Addressing)?

RFC1918 is a standard defined by the Internet Engineering Task Force that specifies private IPv4 address ranges. These addresses are used inside private networks (like your home, office, or cloud VCN in OCI) and are not routable on the public internet. ⚡ Simple Analogy

Think of RFC1918 IPs like:

Apartment numbers inside a building Many buildings can have Apartment 101 But the building address (public IP) is what the outside world sees

📦 The Three RFC1918 Address Ranges 1️⃣ 10.0.0.0/8 (often subnetted like 10.0.0.0/16)

Range: 10.0.0.0 – 10.255.255.255

Very large block (over 16 million IPs)

Common in cloud environments (OCI, AWS, Azure) and large enterprises

In OCI, you might see something like: 10.0.0.0/16 for a VCN

2️⃣ 172.16.0.0/12

Range: 172.16.0.0 – 172.31.255.255

Medium-sized block (~1 million IPs)

Often used in mid-size enterprise networks

3️⃣ 192.168.0.0/16

Range: 192.168.0.0 – 192.168.255.255

Smallest block (~65K IPs)

Used in home networks, Wi-Fi routers Example: your router IP → 192.168.1.1

🧠 Why RFC1918 Exists

Without private IPs:

We’d run out of public IPv4 addresses very quickly Every device would need a globally unique IP

RFC1918 allows:

Reuse of the same IP ranges in different networks Isolation of internal systems Better security and scalability

In Oracle Cloud Infrastructure (OCI):

You create a VCN (Virtual Cloud Network) using RFC1918 ranges Example: VCN CIDR: 10.0.0.0/16 Subnets: 10.0.1.0/24 → Web tier 10.0.2.0/24 → App tier

These IPs:

Stay private Need a NAT Gateway or Internet Gateway to reach the internet

🚀 Quick Summary

RFC1918 defines 3 private IP ranges Used in internal networks and cloud (OCI VCNs) Not routable on the internet Requires NAT or gateways for external access