Multiple IP addresses can be assigned to a local network interface with each local IP address possibly belonging to multiple network aggregations. IPv6 unicast addresses can be assigned to local interfaces in addition to IPv4 addresses.

Since local IPv6 addresses might have different prefix lengths, address scopes, or other address properties, IPv6 implementations have multiple possibilities for source address selection and destination address preference when initiating communication. RFC 3484, “Default Address Selection for IPv6,” defines a set of default algorithms for selecting source and destination addresses so that developers and administrators can predict the behavior of their systems.

You can specify that default address selection be based on a set of predefined default policies as defined by RFC 3484 by using the IPv6 Default Address Selection (IPv6DAS) option of the TCPIP OPTION (OPT) command. This option enables or disables the use of the IPv6 default address selection algorithms for source and destination address selection as follows.

To enable the IPv6DAS option so that default address selection is based on a set of predefined default policies as defined by RFC 3484, enter the following. These default policies can be changed using the TCPIP Address Selection Policy command as described in the following subsection.

NW TCPIP OPT + IPv6DefaultAddressSelection

To disable IPv6DAS, enter the following:

NW TCPIP OPT – IPv6DefaultAddressSelection

When disabled, the default behavior is identical to that used in IPv4. In a multi-homed environment where there is more than one interface to the same network, local address selection is performed in a round-robin fashion. This distributes the TCPIP dialogs among the available interfaces. The IPv6 Default Address Selection option is disabled by default.