4.5. Application and Higher Level Protocol Issues

4.5. Application and Higher Level Protocol Issues

Application and other higher level protocols can treat Local IPv6 addresses in the same manner as other types of global unicast addresses. No special handling is required. This type of address may not be reachable, but that is no different from other types of IPv6 global unicast address. Applications need to be able to handle multiple addresses that may or may not be reachable at any point in time. In most cases, this complexity should be hidden in APIs.

From a host's perspective, the difference between Local IPv6 and other types of global unicast addresses shows up as different reachability and could be handled by default in that way. In some cases, it is better for nodes and applications to treat them differently from global unicast addresses. A starting point might be to give them preference over global unicast, but fall back to global unicast if a particular destination is found to be unreachable. Much of this behavior can be controlled by how they are allocated to nodes and put into the DNS. However, it is useful if a host can have both types of addresses and use them appropriately.

Note that the address selection mechanisms of [ADDSEL], and in particular the policy override mechanism replacing default address selection, are expected to be used on a site where Local IPv6 addresses are configured.