Prefix information option for router advertisements

A router advertisement can contain prefix information options. Each prefix information option contains an IPv6 prefix and flags that indicate how the prefix can be used.

A prefix information option contains two flags:

An on-link flag, which indicates whether on-link processing needs to be performed for the prefix on the shared link. When a prefix is on-link, the addresses in that prefix can be reached on that link without going through a router.
An autonomous flag, which indicates whether autoconfiguration processing needs to be performed for the prefix on the shared link.

The sending router can set one flag or both flags in the prefix information option.

On-link processing

The sending router indicates that a prefix is on-link by setting the on-link flag and specifying a nonzero value for the Valid Lifetime value for the prefix. If the prefix information option indicates that the prefix is on-link, the following criteria are true:

z/OS® Communications Server adds an IPv6 dynamic direct route (if it was not already added by a previous advertisement).
The destination of the route is the prefix that is being processed.
The interface of the route is the interface on which the advertisement was received.
The length of time that the route remains valid is set or is reset using the Valid Lifetime value from the Prefix Information option.

If a non-replaceable static route exists to this prefix or if a direct route to the prefix was added by OMPROUTE (because the PREFIX parameter was specified on the IPV6_INTERFACE, IPV6_OSPF_INTERFACE, or IPV6_RIP_INTERFACE statement in the OMPROUTE configuration file or because a router advertised by way of IPv6 OSPF that the prefix is on-link), then z/OS Communications Server does not add the dynamic direct route. If a replaceable static route exists to this prefix, the dynamic direct route is added, which replaces the replaceable route. The replaceable static route is reinstated if the dynamic direct route is removed later.

The sending router can indicate that a prefix is no longer on-link by setting the on-link flag and specifying the value 0 for the Valid Lifetime value for the prefix. If an IPv6 dynamic direct route exists for which the destination is the prefix that is being processed and for which the interface is the receiving interface, and that route was added as the result of a received router advertisement (for example, the route was not added by OMPROUTE), then z/OS Communications Server deletes the route.

Address autoconfiguration processing

The sending router can indicate that a prefix is to be used for address autoconfiguration by setting the autonomous flag and specifying a nonzero Valid Lifetime value for the prefix. If the Prefix Information option indicates that the prefix should be used for address autoconfiguration, z/OS Communications Server performs the following actions:

Adds an IPv6 home address to the receiving interface for the public autoconfigured address (if that home address was not added by a previous advertisement)
Adds an IPv6 implicit route for the receiving interface and the public autoconfigured address (if that route was not added by a previous advertisement)
Sets or resets the length of time that the home address and implicit route remain valid, using the Valid Lifetime value from the Prefix Information option
Sets or resets the length of time that the home address remains in the preferred state (not in the deprecated state), using the Preferred Lifetime value from the Prefix Information option

If you configured this interface to support temporary addresses (you configured the TEMPADDRS parameter on the IPCONFIG6 statement and the TEMPPREFIX parameter that is specified on the INTERFACE statement includes the prefix), z/OS Communications Server also performs the following actions:

Adds an IPv6 home address for the receiving interface and for the temporary autoconfigured address (if that home address was not already added by a previous advertisement)
Adds an IPv6 implicit route for the receiving interface and for the temporary autoconfigured address (if that route was not already added by a previous advertisement)
Sets or resets the length of time that the home address and implicit route remain valid, using the Valid Lifetime value from the Prefix Information option and the TEMPADDRS VALIDLIFETIME value that is configured
Sets or resets the length of time that the home address remains in the preferred state (not in the deprecated state), using the Preferred Lifetime value from the Prefix Information option and the TEMPADDRS PREFLIFETIME value that is configured

Restriction: Prefixes that are learned solely by using the Prefix parameter on the OMPROUTE IPV6_INTERFACE, IPV6_OSPF_INTERFACE, or IPV6_RIP_INTERFACE statement are never used for autoconfiguration.

If you manually configure addresses for an IPv6 interface using the INTERFACE statement, addresses for that interface cannot be autoconfigured. If a prefix is not 64 bits in length, it is not used for autoconfiguration of addresses. Unlike the prefix route and the default route, the implicit route and home address cannot immediately be deleted; these items must age out. If the Valid Lifetime value is set to infinity, the implicit route and home address for the public autoconfigured address do not time out. For more information about autoconfiguration, see Stateless address autoconfiguration.