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Introduction to IPv6 address
1.
IPv6 address format
An IPv6 address is represented as a series of 16-bit hexadecimals, separated by colons (:).
An IPv6 address is divided into eight groups, and the 16 bits of each group are represented by
four hexadecimal numbers which are separated by colons, for example,
2001:0d02:0000:0000:0014: 0000:0000:0095. The hexadecimal letters in IPv6 addresses are
not case-sensitive.
To simplify the representation of IPv6 addresses, zeros in IPv6 addresses can be handled as
follows:
Leading zeros in each group can be removed. For example, the above-mentioned address
can be represented in shorter format as 2001:d02:0:0:14:0:0:95.
Two colons (::) may be used to compress successive hexadecimal fields of zeros at the
beginning, middle, or end of an IPv6 address. For example, the above-mentioned address
can be represented in the shortest format as 2001:d02::14:0:0:95.
Note:
Two colons (::) can be used only once in an IPv6 address to represent the longest successive
hexadecimal fields of zeros. Otherwise, the device is unable to determine how many zeros
double-colons represent when converting them to zeros to restore a 128-bit IPv6 address.
An IPv6 address consists of two parts: address prefix and interface ID. The address prefix and
the interface ID are respectively equivalent to the network ID and the host ID in an IPv4
address.
An IPv6 address prefix is represented in "IPv6 address/prefix length" format, where "IPv6
address" is an IPv6 address in any of the above-mentioned formats and "prefix length" is a
decimal number indicating how many leftmost bits from the preceding IPv6 address are used
as the address prefix.
2. IPv6 address classification
IPv6 addresses fall into three types: unicast address, multicast address, and anycast address.
Unicast address: An identifier for a single interface, on a single node. A packet that is sent to
a unicast address is delivered to the interface identified by that address.
Multicast address: An identifier for a set of interfaces (typically belonging to different nodes),
similar to an IPv4 multicast address. A packet sent to a multicast address is delivered to all
interfaces identified by that address. There are no broadcast addresses in IPv6. Their
function is superseded by multicast addresses.
Anycast address: An identifier for a set of interfaces (typically belonging to different
nodes). A packet sent to an anycast address is delivered to one of the interfaces identified
by that address (the nearest one, according to the routing protocols’ measure of distance).
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