IpV6 Autoconfiguration tutorial

5.5.4 Address Lifetime Expiry

A preferred address becomes deprecated when its preferred lifetime expires.

What can, should or must be done with a deprecated address?

	Should continue to be used as a source address in existing communications
	Should not be used in new communications if an alternate (non-deprecated) address is available and has sufficient scope.
	IP and higher layers (e.g., TCP, UDP) must continue to accept datagrams destined to a deprecated address since a deprecated address is still a valid address for the interface.
	An implementation may prevent any new communication from using these addresses.
	System management must have the ability to disable the prevention above, and the facility must be disabled by default.

An address becomes invalid when its valid lifetime expires.

An invalid address must not be used as a source address in outgoing communications and must not be recognized as a destination on a receiving interface.