Editing IPv6 (section)

==IPv6 in the Domain Name System==
In the [[Domain Name System]] (DNS), [[hostname]]s are mapped to IPv6 addresses by [[AAAA record|AAAA]] ("quad-A") resource records. For [[Reverse DNS lookup|reverse resolution]], the IETF reserved the domain [[.arpa|ip6.arpa]], where the name space is hierarchically divided by the 1-digit [[hexadecimal]] representation of [[nibble]] units (4 bits) of the IPv6 address. This scheme is defined in {{IETF RFC|3596}}.

When a dual-stack host queries a DNS server to resolve a [[fully qualified domain name]] (FQDN), the DNS client of the host sends two DNS requests, one querying A records and the other querying AAAA records. The host operating system may be configured with a preference for address selection rules {{IETF RFC|6724}}.<ref>{{Cite book|title=IPv6 Essentials: Integrating IPv6 into Your IPv4 Network|author=Silvia Hagen|publisher=O'Reilly Media, Inc.|year=2014|isbn=9781449335267|pages=176}}</ref>

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An alternative record type was used in early DNS implementations for IPv6, designed to facilitate network renumbering, the ''A6'' records for the forward lookup and a number of other innovations such as ''bit-string labels'' and ''[[CNAME record#DNAME record|DNAME]]'' records. It is defined in {{IETF RFC|2874}} and its references (with further discussion of the pros and cons of both schemes in {{IETF RFC|3364}}), but has been deprecated to experimental status ({{IETF RFC|3363}}).