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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  Name Systems and TCP/IP Name Registration and Name Resolution            9  TCP/IP Name Systems: Host Tables and Domain Name System (DNS)                 9  TCP/IP Domain Name System (DNS)

DNS Master File Format 1 2 Network File and Resource Sharing Protocols and the TCP/IP Network File System (NFS)

Proposed Changes to the IPv6 DNS Extensions

In 2000, the IETF published RFC 2874, DNS Extensions to Support IPv6 Address Aggregation and Renumbering. This standard proposed a replacement for the IPv6 support introduced in RFC 1886, using a new record type, A6, instead of 1886's AAAA. The main difference between AAAA and A6 records is that the former are just whole addresses like A records, while A6 records can contain either a whole or partial address.

The idea behind RFC 2874 was that A6 records could be set up in a manner that complements the IPv6 format for unicast addresses. Then, name resolution would involve a technique called chaining to determine a full address for a name from a set of partially-specified address components. In essence, this would make the addresses behave much the way hierarchical names themselves work, providing some potential flexibility benefits.

For a couple of years, both RFC 1886 and RFC 2874 were proposed standards, and this led to considerable confusion. In August 2002, RFCs 3363 and 3364 were published, which clarified the situation with these two proposals. RFC 3363 represents the “Supreme Court decision”, which was that RFC 2874 and the A6 record be changed to experimental status and the AAAA record of RFC 1886 be kept as the DNS IPv6 standard.

The full explanation for the decision can be found in RFC 3364. In a nutshell, it boiled down to the IETF believing that there were significant potential risks in the successful implementation of RFC 2874. While the capabilities of the A6 record were “interesting”, it was not clear that they were needed, and given those risks, they felt sticking with RFC 1886 was the better move.

DNS Master File Format 1 2 Network File and Resource Sharing Protocols and the TCP/IP Network File System (NFS)