An IP address (Internet Protocol address) is a numerical identifier assigned to every device connected to a network. It enables devices to locate each other and exchange data across local networks and the global internet.
Today’s networking relies on two versions of the protocol:
- IPv4: 32-bit addressing (e.g.,
192.168.1.1), offering ~4.3 billion addresses - IPv6: 128-bit addressing (e.g.,
2001:db8::1), providing an effectively inexhaustible address space
Understanding how private and public IP ranges are defined is fundamental to grasping modern networking and internet scalability.
🏠 Private IP Address Ranges (LAN) #
Private IP addresses are reserved for local networks and are not routable on the public internet. This allows millions of independent networks to reuse the same address space without conflict.
Devices using private IPs access the internet through Network Address Translation (NAT), where a router translates private addresses into a public one.
The Internet Assigned Numbers Authority (IANA), via RFC 1918, defines the following IPv4 private ranges:
IPv4 Private Address Blocks #
| Class | Start Address | End Address | Total Addresses | Common Usage |
|---|---|---|---|---|
| Class A | 10.0.0.0 | 10.255.255.255 | 16,777,216 | Large enterprises, internal backbones |
| Class B | 172.16.0.0 | 172.31.255.255 | 1,048,576 | Campuses, mid-sized organizations |
| Class C | 192.168.0.0 | 192.168.255.255 | 65,536 | Home networks, small offices |
These ranges are intentionally excluded from global routing tables, ensuring they remain local-only.
🌍 Public IP Address Ranges (WAN) #
Public IP addresses are globally unique and routable across the internet. They are allocated by IANA and distributed through Regional Internet Registries (RIRs) to ISPs, cloud providers, and enterprises.
Any device or service intended to be reachable from the internet—such as a website or mail server—must ultimately use a public IP address.
IPv4 Public Address Space #
Public IPv4 addresses include nearly all ranges not reserved for private or special purposes, such as:
1.0.0.0 – 9.255.255.25511.0.0.0 – 126.255.255.255128.0.0.0 – 223.255.255.255
Special-Use IPv4 Addresses #
Some address ranges are neither public nor private, but reserved for specific technical roles:
- Loopback:
127.0.0.1— local host communication - Link-Local (APIPA):
169.254.0.0/16— automatic fallback when DHCP fails - Broadcast:
255.255.255.255— sends traffic to all devices on a subnet
🌐 IPv6 Addressing: Redefining Private and Public #
IPv6 was designed to eliminate address exhaustion and reduce dependence on NAT. While the concepts of “private” and “public” still exist, they are implemented differently.
Key IPv6 Address Types #
-
Global Unicast (Public):
2000::/3
Globally routable, unique addresses used on the public internet -
Unique Local Addresses (ULA / Private):
fc00::/7
IPv6’s equivalent of private IPv4 addresses, intended for internal networking -
Link-Local Addresses:
fe80::/10
Automatically assigned and valid only within a single local link or subnet
Unlike IPv4, IPv6 allows most networks to operate with globally unique addresses without NAT, simplifying routing and end-to-end connectivity.
📊 Private vs Public IP Comparison #
| Feature | Private IP | Public IP |
|---|---|---|
| Scope | Local network only | Global internet |
| Uniqueness | Local uniqueness | Globally unique |
| Internet Reachability | Requires NAT | Directly routable |
| Cost | Free to use | Allocated by ISPs/RIRs |
| Visibility | Hidden from internet | Internet-visible |
🧠 Key Takeaway #
Private and public IP ranges are a cornerstone of internet scalability. Private addressing, combined with NAT, enabled the explosive growth of IPv4 networks, while IPv6 restores end-to-end connectivity with an effectively limitless address space.
Understanding these boundaries is essential for anyone working with networking, infrastructure, or cloud systems.