We assume that the reader has a good general understanding of the Domain Name System (DNS). Many aspects of the DNS are unaffected by IPv6, because it was designed on very general principles.
A specific Resource Record type is defined to embed IPv6 addresses: the AAAA Record [RFC3596]. This simply provides a 128 bit IPv6 address in the same way that an A record provides an IPv4 address. (AAAA is normally pronounced "Quad-A".)
Similarly, reverse lookup is enabled by the IP6.ARPA domain. This is
done using 4-byte nibbles respresented as hexadecimal characters, so the
address 2001:db8:4006:80b:a1b3:6d7a:3f65:dd13 will appear as
3.1.d.d.5.6.f.3.a.7.d.6.3.b.1.a.b.0.8.0.6.0.0.4.8.b.d.0.1.0.0.2.IP6.ARPA.
Clearly, these entries are for computers, not for humans.
A corollary of defining the AAAA record is that DNS lookups that indirectly cause an A record lookup must also cause a AAAA lookup. This concerns NS, SRV and MX lookups.
This change also affects API calls that involve the DNS. The old
gethostbyname() and gethostbyaddr() calls are OBSOLETE and
should no longer be used. They are replaced by getaddrinfo() and
getnameinfo(), which handle IPv6 as well as IPv4. In particular,
getaddrinfo() provides the programmer with a list of both IPv6 and
IPv4 addresses, and it is the programmer's job to decide which one to
use. The order in which addresses are presented to the programmer is
determined by a local configuration table on the host, in a way
described by RFC6724.
Unfortunately there is no standard mechanism for remote configuration of
this table. Operators need to be aware of this complexity when
attempting to cause users to favor IPv6 over IPv4 (or the converse).
Apart from this, in an ideal world DNS for IPv6 should not cause extra operational issues. However, in practice, there are some matters of concern:
-
As noted in 2. Managed configuration, the DNS server for a subnet must be announced by a Router Advertisement even if DHCPv6 is in use.
-
DNS IPv6 Transport Operational Guidelines are documented in BCP91.
-
Considerations for Reverse DNS in IPv6 for Internet Service Providers are documented in RFC8501.
-
It is not unknown for some sites to register IPv4-mapped IPv6 addresses, e.g.
::ffff:198.51.100.99, with AAAA records. While this seems to work in most cases, it is inappropriate if the host in question has a valid IPv6 address, and pointless otherwise.
Some statistics on AAAA records and reachability may be found at Dan Wing's site.