IPv6 Network - Representing IPv6 Information in the DNS

Ignoring caching for a moment, every DNS request involves the root nameservers, TLD servers and the destination’s nameserver, and often nameservers from the initiator’s and/or destination’s ISPs. Requiring all those nameservers to be upgraded to support IPv6 in order to be able to look up IPv6 addresses in the DNS would make it almost impossible to deploy IPv6. Fortunately, this isn’t necessary. In 1995, RFC 1886 described a very straightforward way to publish IPv6 information in the DNS that provided an easy upgrade path. However, in 2000, a more ambitious way to do the same was published in RFC 2874. This new mechanism was partially implemented, but more detailed analysis and practical experience showed that it was perhaps a bit too ambitious, so around 2001, the IETF started moving away from the new method, and in 2003, RFC 1886 was reinstated for the most part but with one small, yet important change (RFC 3596).

Purists always type a period at the end of an FQDN, to indicate that it’s an FQDN. This stops the resolver from thinking it needs to stick the local domain name to the end. In the example.com network, www.kame.net may mean www.kame.net.example.com or www.kame.net, but www.kame.net. is always www.kame.net.

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