Stateless address autoconfiguration

The larger address field of IPv6 solves a number of problems inherent in IPv4, but the size of the address itself might be a potential problem for the TCP/IP administrator. As a result, IPv6 has the capability to automatically assign an address to an interface at initialization time. In this way, a network can become operational with minimal action on the part of the TCP/IP administrator. Stateless autoconfiguration is supported for an OSA-Express QDIO interface in z/OS® Communications Server if no manually configured addresses are defined on the interface. Manual configuration of the host's local addresses is not required except for VIPA interfaces. Stateless address autoconfiguration consists of the following steps:

During interface startup, the host generates its own addresses by using a combination of router advertised prefixes and the interface ID. If the INTFID parameter is configured on the INTERFACE statement, the value that is configured on the parameter is used as the interface ID. Otherwise, the host obtains an interface token from the interface hardware to create an interface ID.
If temporary addresses are supported on the interface (the TEMPADDRS parameter is configured on the IPCONFIG6 statement and the TEMPPREFIX parameter is configured on the INTERFACE statement), a random interface ID is generated. Temporary addresses are generated using a combination of router-advertised prefixes and the random interface ID.
Duplicate address detection is performed for each address. If a duplicate is not detected or Duplicate Address Detection (DAD) is disabled for the interface (DUPADDRDET 0 specified on the INTERFACE statement), the local address is added.
A stateless autoconfigured address is deleted when its valid lifetime expires or when a manually defined address is added to the interface.
An IPv6 address generated using stateless address autoconfiguration has two timers associated with it: A preferred lifetime timer and a valid lifetime timer. Router advertisements contain the valid lifetime and preferred lifetime timers for a prefix. Temporary autoconfigured addresses also have a valid lifetime and preferred lifetime timer configured on the IPCONFIG6 statement (TEMPADDRS PREFLIFETIME value VALIDLIFETIME value). The valid and preferred lifetime timers for a temporary autoconfigured address are the lesser of the values contained in the router advertisement for the prefix and the value specified on the IPCONFIG6 statement. The valid and preferred lifetime timers for a public autoconfigured address are the values that are in the router advertisement for the prefix.

An IPv6 address goes through two phases to gracefully handle the address expiration:
Preferred

Use is unrestricted.

Deprecated

In anticipation of the expiration of the leased period, use of the address is discouraged.

When the preferred lifetime expires, the address created from the prefix is deprecated. When the valid lifetime expires, the address created from the prefix is deleted and an operator message is issued.