Most computers on the internet today are configured with private addresses that share the use of a single public address installed on a firewall or home router. When the user connects to an internet server such as a web site, the connection is handled by the router that makes the connection using its public address and then forwards the response to the requester. During this transaction, the This is referred to as Network Address Translation (NAT).
A typical example of an IPv4 private address is:
Since private addresses are not routed on the internet, the same private addresses can be reused across the internet without any conflict. The use of private addresses has extended the limited supply of IPv4 addresses since large numbers of computers can share the use of a small number of routable IPv4 addresses.
In the IPv6 protocol, private addresses are used for different purposes, rather than for NAT. Also, in IPv6, network interfaces typically have multiple addresses, some of which are private addresses.
Private or local addresses in the IPv6 protocol include Unique Local Addresses and Link Local Addresses:
Unique Local Address (ULA) is an IPv6 address in the block:
It is the IPv6 counterpart of the IPv4 private address and is used in private networks, They are not routable in the global IPv6 Internet.
Link Local Address is an IPv6 address in the block:
It used only on a local network link for functions such as address resolution or neighbor discovery. They are not routed, even locally.