Public vs. Private IP Addresses

1. Public IP Addresses

Public addresses are globally unique identifiers and are Internet-routable.

Key Characteristics:

• Assignment: They are assigned and regulated by Internet Service Providers (ISPs) under the coordination of global authorities like IANA and RIRs (such as RIPE, ARIN, etc.).
• Visibility: Any device directly connected to the global network requires a public IP to be reachable from the outside (web servers, edge routers, etc.).
• Cost: They are usually limited and often have an associated cost, especially commercial static IPs.

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2. Private IP Addresses

Private addresses are reserved exclusively for use within a Local Area Network (LAN).

Routing Rule: They are not routable on the Internet. If a core internet router detects a packet with a private IP as its source or destination, it drops it immediately for security reasons.

RFC 1918 Standard

The private addressing space is defined by the RFC 1918 standard, which divides these IPs into three main blocks based on network size (adapted classful addressing):

Class	Private Network Range	Available IPs per Block	Typical Use / Use Cases
Class A	10.0.0.0 – 10.255.255.255	~16.7 million	Large corporations (Enterprise), cloud infrastructures (AWS/Azure VPCs).
Class B	172.16.0.0 – 172.31.255.255	~65,536 per subnet	Medium-sized networks, educational campuses, container environments (Docker/LXC).
Class C	192.168.0.0 – 192.168.255.255	256 per subnet	Home networks (SOHO residential routers) and small offices.