لطفا منتظر باشید ...
11.5 The ABCs of IPv6 Addressing
The Microsoft DNS Server supports the new AAAA record necessary for
IPv6. We thought some information on the representation and structure
of IPv6 addresses would be appropriate to help you understand the
record.IPv6 addresses are 128 bits long. The preferred representation of an
IPv6 address is eight groups of as many as four hexadecimal digits,
separated by colons. For example:
0123:4567:89ab:cdef:0123:4567:89ab:cdef
The first group of hex digits (0123, in this example) represents the
most significant (or highest order) four bits of the address.Groups of digits that begin with one or more zeros
don't need to be padded to four places, so you can
also write the previous address as:
123:4567:89ab:cdef:123:4567:89ab:cdef
Each group must contain at least one digit, though, unless
you're using the :: notation. The :: notation allows
you to compress sequential groups of zeros. This comes in handy when
you're specifying just an IPv6 prefix. For example,
this notation:
dead:beef::
specifies the first 32 bits of an IPv6 address as
dead:beef and the remaining 96 as zeros.You can also use :: at the beginning of an IPv6 address to specify a
suffix. For example, the IPv6 loopback address is commonly written
as:
::1
or 127 zeros followed by a single one. You can even use :: in the
middle of an address as a shorthand for contiguous groups of zeros:
dead:beef::1
You can use the :: shorthand only once in an address since more than
one could be ambiguous.IPv6 prefixes are specified in a format similar to
IPv4's CIDR notation. As many bits of the prefix as
are significant are expressed in the standard IPv6 notation, followed
by a slash and a decimal count of exactly how many significant bits
there are. So the following three prefix specifications are
equivalent (though obviously not equivalently terse):
dead:beef:0000:00f1:0000:0000:0000:0000/64
dead:beef::00f1:0:0:0:0/64
dead:beef:0:f1::/64
11.5.1 IPv6 Forward and Reverse Mapping
Clearly,
the existing A record
won't accommodate IPv6's 128-bit
addresses. RFC 1886 defines the solution: an address record
that's four times as long as an A record.
That's the AAAA (pronounced
"quad A") record. The
AAAA record takes as its record-specific data the textual format of
an IPv6 record as described earlier. So for example,
you'd see AAAA records like this one:
ipv6-host IN AAAA 4321:0:1:2:3:4:567:89ab
RFC 3152 established
ip6.arpa,
a new reverse-mapping namespace for IPv6 addresses.[6] Each level of subdomain under
ip6.arpa represents four bits of the 128-bit
address, encoded as a hexadecimal digit just like in the
record-specific data of the AAAA record. The least significant
(lowest order) bits appear at the far left of the domain name. Unlike
the format of addresses in AAAA records, omitting leading zeros is
not allowed, so there are always 32 hexadecimal digits and 32 levels
of subdomain below ip6.arpa in a domain name
corresponding to a full IPv6 address. The domain name that
corresponds to the address in the previous example is:[6] Several aspects of IPv6 addressing have been a moving target
within the Internet standards community. We should point out that the
original domain for IPv6 reverse mapping as defined in RFC 1886 was
ip6.int. This domain was changed to
ip6.arpa by RFC 3152 for both technical and
political reasons.
b.a.9.8.7.6.5.0.4.0.0.0.3.0.0.0.2.0.0.0.1.0.0.0.0.0.0.0.1.2.3.4.ip6.arpa.
These domain names
have
PTR records attached, just as the
domain names under in-addr.arpa do:
b.a.9.8.7.6.5.0.4.0.0.0.3.0.0.0.2.0.0.0.1.0.0.0.0.0.0.0.1.2.3.4.ip6.arpa. IN PTR
mash.ip6.movie.edu.
