Public vs Private IP Addresses: What's the Difference?

A public IP address comes from address space intended for routing on the public internet. A private IP address is used inside private networks and is not globally routable. Homes, offices, and cloud networks use private addresses for internal connections and public addresses for internet-facing communication.

The public/private distinction usually refers to IPv4. IPv6 has its own address categories, explained below. For the underlying concept, read What Is an IP Address?.

Public vs private IP addresses at a glance

The ability to reuse private space is a deliberate part of RFC 1918, the private IPv4 addressing standard.

What is a public IP address?

A public IP address provides an address that other networks can route traffic toward across the internet. Providers assign public addresses to connections and services; organizations can also use public address ranges they are authorized to manage.

Public addresses might be used by a home router, a website’s public endpoint, or a business VPN gateway. The wider allocation system is described in IANA’s number resources overview.

Public does not mean open. A service still needs working routing, a listening application, and access rules that allow the connection. A firewall can block incoming traffic even when the destination has a public address.

What is a private IP address?

A private IPv4 address identifies a connection inside a private network. For example, your laptop might use 192.168.1.20, while a printer uses 192.168.1.30.

An unrelated home can reuse those same addresses because its network is separate. If two networks with overlapping ranges are later connected, such as through a business VPN, the overlap can cause routing conflicts. Address planning becomes important when private networks need to communicate. RFC 1918 discusses this tradeoff.

Private addressing also works across routed internal networks. It is not limited to devices connected to one Wi-Fi router.

What are the private IPv4 address ranges?

IANA lists three private-use ranges:

The slash notation is a compact way to describe an address block. The range columns show exactly which addresses it covers.

Not every address starting with 172 is private. Only addresses from 172.16.0.0 through 172.31.255.255 fall within that private range.

Also, an address outside these three ranges is not automatically public. IPv4 has other special-purpose ranges. For example, 127.0.0.1 is a loopback address that refers back to the local device, while 169.254.0.0/16 is link-local space. These are separate from private-use space in IANA’s IPv4 special-purpose registry.

How does a private IP address access the internet?

In a typical home IPv4 network, the router uses network address translation, or NAT.

Imagine a laptop at 192.168.1.20 opening a website:

1. The laptop sends traffic toward the website through the router.
2. The router translates the outgoing source address to its public IPv4 address. In a common address-sharing setup, it also tracks port mappings to distinguish connections.
3. The website replies to the public address.
4. The router uses the mapping to deliver the reply to the laptop.

This allows multiple devices to share one public IPv4 address. The address-and-port translation mechanism is described in RFC 3022.

Why is my router’s address different from an IP checker’s result?

First, check which router address you are viewing. Its LAN address belongs to the local network; its WAN address belongs to the connection toward the provider. These serve different purposes.

Some providers also use carrier-grade NAT, or CGNAT, so multiple customers share public IPv4 space. A range reserved for this use is 100.64.0.0/10, covering 100.64.0.0 through 100.127.255.255. It is shared address space, distinct from the three private ranges. RFC 6598 defines it.

If your router receives a shared or private WAN address, an external IP checker may show the provider’s translated public address. A VPN, another upstream router, or comparing IPv4 with IPv6 can also explain a mismatch.

Are public and private IP addresses static or dynamic?

Either can be static or dynamic. Public/private describes where an address can be used; static/dynamic describes how its assignment is managed.

A business may keep a static public address for a service. A printer may have a fixed private address so local computers can find it consistently. Other devices receive dynamic assignments. DHCP supports both dynamic and administratively fixed allocation, as described in RFC 2131.

Does IPv6 have private addresses?

IPv6 uses different categories:

• Global unicast addresses are used for globally routable communication, subject to routing and firewall rules.
• Unique local addresses, or ULAs, support communication within sites or between cooperating sites. They are not intended for routing on the global internet. The range is fc00::/7; locally assigned ULAs use the fd00::/8 half. RFC 4193 defines ULAs.
• Link-local addresses, from fe80::/10, support communication on a single network link and are not forwarded by routers. They are defined in RFC 4291.

A device can have several IPv6 addresses for different purposes. The usual IPv4 pattern of private addresses sharing one public address is not a requirement for IPv6. Read IPv4 vs IPv6 for a broader comparison.

How does this relate to BYOIP?

Bring Your Own IP concerns eligible public address space that an organization controls and wants to use with a supporting provider. Private ranges such as 192.168.0.0/16 do not establish exclusive control because unrelated networks can reuse them.

For a business, the question is whether it needs continuity for its public addresses when changing infrastructure. Internal private addressing is a separate part of its network design.

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