What is a Public IP Address?

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An IP address is considered public if it can be used on the Internet. Public IP addresses have different IP number ranges than private IP addresses.

How a Public IP Address Works 

Public IP addresses are used by Internet servers including those for Web sites and DNS serversbroadband routers and other network gateways, or any computer connected directly to the Internet.

Each public address belongs to a range or block of addresses.

The Internet Assigned Numbers Authority (IANA) controls ownership of these IP ranges and assigns each block to organizations such as Internet Service Providers (ISPs) who in turn allocate individual IP addresses to customers.

Consumers normally receive one public IP address when they subscribe to an Internet service plans. Some higher-priced plans offer several IP addresses rather than one, useful for Small Office / Home Office (SOHO) networks. Business Internet plans give organizations a range (block) of public IP addresses.

Home Internet plans do not assign any one specific IP number to a home network. Instead, residential ISPs allocate households any currently available address from their pool, then reclaims that address if a customer stops using it. This helps conserve the limited number of available public addresses each ISP owns.

Most Common Public IP Addresses

Among the many millions of IP addresses in use on the Internet today, certain ones appear much more commonly than others:

  • the addresses of public DNS servers. Internet users apply these addresses to their devices, which are in turn used to support Domain Name Service lookups.

Public Addressing in IPv6

The newest version of Internet Protocol - IPv6 - uses a different numbering system than the traditional IP (IPv4) listed above. As with IPv4, IPv6 also reserves a specific range of addresses for private use. Other than this one range (any address which begins with "fdxx:"), the rest of IPv6 addresses are public.

IPv6 provides a much larger number of public IP addresses than IPv4.  While Internet providers must carefully control their IPv4 public address allocation due to shortage of supply, IPv6 provides nearly unlimited addressing options.

Restrictions on Public IP Address Numbers

All public IP addresses fall outside the ranges reserved for private uses by Internet standards groups. Specifically all IP addresses that start with "10." (10.x.x.x) or "192.168." (192.168.x.x) fall within private ranges, as do any addresses between 172.16.0.0 and 172.31.255.255.

Most networks also do not allow IP addresses that end with ".0" or ".255" to be used by client devices.