Configuring Name Services

A dual node must determine if the peer can support IPv6 or IPv4 in order to know which IP version to use when transmitting. Controlling what information goes in the name service accomplishes this. You define an IPv4 node's IP address and the IPv6 node's IP address in the name service. Thus, a dual node has both addresses in the name service.

However, the presence of an IPv6 address in the name service also signifies that the node is reachable, using IPv6 from all nodes that get information from that name service. For example, placing an IPv6 address in NIS implies that the IPv6 host is reachable using IPv6 from all IPv6 and dual nodes that belong to that NIS domain. Placing an IPv6 address in global DNS requires that the node is reachable from the Internet IPv6 backbone. This is no different than in IPv4 where, for example, mail delivery and HTTP proxy operation depend on there being only IPv4 addresses for nodes that can be reached using IPv4. When no reachability exists in IPv4, for instance, due to firewalls, the name service must be partitioned into an inside firewall and outside firewall database so that IPv4 addresses are visible only where they are reachable.

The protocol used to access the name service (DNS, NIS, NIS+, or something else) is independent of the type of address that can be retrieved from the name service. This name service support, coupled with dual stacks, allows a dual node to use IPv4 when communicating with IPv4-only nodes and use IPv6 when communicating with IPv6 nodes, provided that there is an IPv6 route to the destination.