In IPv4, private addresses are common and are used for internal networks, separated from the public Internet through NAT (Network Address Translation). IPv6, however, handles this concept differently due to its large address space.

IPv6 does not have “private” addresses in the same sense as IPv4. Instead, it uses several types of addresses for specific purposes that can be considered analogous to private addresses in certain contexts:

Unique Local Addresses (ULAs)

Unique local addresses (ULAs) in IPv6 are similar to private addresses in IPv4. They are designed for internal use within private networks and are not intended to be routed on the public internet. These addresses begin with the prefix fc00::/7, although the prefix fd00::/8 It is commonly used to generate ULA addresses randomly and with low risk of collision on different networks.

Characteristics of the ULAs:

• Not Globally Routable: ULAs are not recognized by Internet routers, which means they cannot be used for traffic crossing the Internet.
• Possible Uniqueness: Although ULAs are not guaranteed by a central authority, the address space is large enough to make duplication very unlikely when randomly generated.
• Self-containment: Ideal for internal communication of a network, limiting the need for renumbering if connectivity to the Internet or between different internal networks is reconfigured.

Link Local Addresses

Link-local addresses in IPv6 are another type of address that is only valid and unique on a specific physical link (for example, a LAN). These addresses start with fe80::/10 and are similar to APIPA (Automatic Private IP Addressing) automatic addresses in IPv4.

Use:

• Local Communication: Useful for communication between devices on the same network segment or local link without the need for prior configuration.
• Initial Operations: Used for operations such as initial device configuration, service discovery, and configuring other types of addresses.

In summary, although IPv6 does not use the concept of private addresses in the same way as IPv4, it offers ULAs and link-local addresses that provide similar functionality for scenarios where global connectivity is not desired or needed.