5.2. From the Standpoint of a Site

5.2. From the Standpoint of a Site

There are a number of design factors in IPv6 local addresses that reduce the likelihood that IPv6 local addresses will be used as arbitrary global unicast addresses. These include:

• The default rules to filter packets and routes make it very difficult to use IPv6 local addresses for arbitrary use across the Internet. For a site to use them as general purpose unicast addresses, it would have to make sure that the default rules were not being used by all other sites and intermediate ISPs used for their current and future communication.

• They are not mathematically guaranteed to be unique and are not registered in public databases. Collisions, while highly unlikely, are possible and a collision can compromise the integrity of the communications. The lack of public registration creates operational problems.

• The addresses are allocated randomly. If a site had multiple prefixes that it wanted to be used globally, the cost of advertising them would be very high because they could not be aggregated.

• They have a long prefix (i.e., /48) so a single local address prefix doesn't provide enough address space to be used exclusively by the largest organizations.