What Are Private IP Addresses?

By Stephen Bucaro

Normally you have to be assigned an IP address, or a group of IP addresses by one of the five Regional Internet Registries (RIRs). In turn, the RIRs receive their allocation of IP addresses from the The Internet Assigned Numbers Authority (IANA). However, if you just need IP addresses for an internal network that will not be routed to the Internet, you can select from blocks of IP addresses reserved as Private IP addresses.

Private IP addresses are not assigned to any specific organization, you can use them for your own internal network as you please. However, if you try to get on the Internet with a Private IP address, the first router your transmission comes upon will recognize that they use a private address and will just drop your packets.

IPv4 Private Address Ranges

Your network using private IP addresses can still connect to the Internet through a proxy server, a server with a non-private IP Address that all computers on your network have to go through to access the Internet.

Or you can connect to the Internet by using a Network Address Translation (NAT) gateway, a server with a pool of non-private IP Addresses that will convert your computers private IP Address into one of the non-private IP Addresses in its pool and send your transmission over the Internet, and convert the Internet's response back into your computers private IP Address.

IPv6 also has private IP addresses, except with IPv6 they're called Unique Local Addresses (ULA). The IPv6 address block fc00::/7 has been allocated for private IP addresses, that's approximately 1.1 trillion addresses.

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