RFC 4193, Unique Local IPv6 Unicast Addresses, defines unique local addresses (ULAs), which are IPv6 unicast addresses. They can be considered IPv6 equivalents of the private IPv4 addresses identified in RFC 1918, Address Allocation for Private Internets, which cannot be routed globally.

A ULA is globally unique, but not expected to be globally routable. It is intended for local communications and to be routable in a limited area such as a site or among a small number of sites. Palo Alto Networks^® does not recommend that you assign ULAs, but a firewall configured with NPTv6 will translate prefixes sent to it, including ULAs.