Domain Name System
Zone File Contents

Each interface node has more IPv6 addresses with different scope and lifetime. For this reason, the following question arose: "What IPv6 addresses should be written into a zone file?" All IPv6 Global Unicast addresses and addresses used for transition mechanisms with long-term lifetime should certainly be written into a zone file. On the other hand, the Link-Local addresses and randomly generated addresses with short-term lifetime that are used for privacy should not be written into a zone file.

For other IPv6 addresses, especially those that are assigned by stateless or stateful address auto-configuration, there is not any universal recommendation. These addresses have mostly short-term lifetime, so their inclusion would require the deployment of dynamic DNS updates.

Another question arises when a computer communicates via two protocols: "What address type does a computer use?" There are two fundamental approaches:

The Same Domain Name

If host.cvut.cz computer has the IPv4 address 192.168.121.57 and IPv6 address 2001:718:8DE:128:3201:A1FF:FE67:12, the following entries will be included in a zone file for cvut.cz domain:

Example of Entries for the Same Domain Name

If the pc computer wants to communicate with host.cvut.cz computer, the DNS server sends both addresses to the pc computer that selects the appropriate address based on the communication protocol. When the pc computer communicates with both protocols, IPv6 will take precedence because the current operating systems prefer IPv6.

Currently, this approach is not entirely reliable due to lack of IPv6 implementation. If the establishing an IPv6 connection fails, an IPv4 connection will be established for TCP communication. The TCP protocol provides mechanisms for reliable delivery of data due to which the computer finds out that the IPv6 network is not functional. But the interval required for detecting malfunction of IPv6 network can be up to several minutes. In the case of UDP communication, the connection is not established at all.

Different Domain Names

In the case of different domain names, it is usually specify a subdomain (often called ip6 or ipv6) in which IPv6 addresses are included. From the domain name directly implies the use of the communication protocol.

Then the zone file for host.cvut.cz computer should contain the following entries:

Example of Entries for Different Domain Names

Most likely, this is a temporary option than the IPv6 implementation will be wholly accessible.