An Internet Protocol Version $6$ address $($IPv$6$ address$)$ is a numerical label that is used to identify

a network interface of a computer or a network node participating in an IPv$6$ computer network and

for locating it in the network.

IPv$6$ addresses have a size of $128$ bits. An IPv$6$ address is represented as eight groups of four

hexadecimal digits, each group representing $16$ bits $($two octets, a group sometimes also called

a hextet$).$ The groups are separated by colons $(.$

An example of an IPv$6$ address is:

$2001$:$0$db$8$:$85$a$3$:$0000$:$0000$:$8$a$2$e:$0370$:$7334$

The hexadecimal digits are case$-$insensitive, but IETF recommendations suggest the use of lower

case letters.

In an attempt to simplify IPv$6$ addresses, the standards provide flexibility in their representation.

However, this also complicates several common operations: searching for a specific address in a

text file or stream, and comparing two addresses to determine their equivalence.

To mitigate these problems, a canonical format is defined for rendering IPv$6$ addresses in text:

Leading zeros in each $16-$bit field are suppressed. For example, $2001$:$0$db$8$::$0001$ is rendered

as $2001$:db$8$::$1,$ though any all$-$zero field that is explicitly presented is rendered as $0.$

$"$ :$\text{'}"$ is not used to shorten just a single $0$ field. For example, $2001$:db$8$:$0$:$0$:$0$:$0$:$2$:$1$ is shortened

to $2001$:db$8$::$2$:$1,$ but $2001$:db$8$:$0000$:$1$:$1$:$1$:$1$:$1$ is rendered as $2001$:db$8$:$0$:$1$:$1$:$1$:$1$:$1.$

Representations are shortened as much as possible. The longest sequence of consecutive all$-$

zero fields is replaced with double$-$colon. If there are multiple longest runs of all$-$zero fields, then

it is the leftmost that is compressed. E$.$g$.,2001$:db$8$:$0$:$0$:$1$:$0$:$0$:$1$ is rendered

as $2001$:db$8$::$1$:$0$:$0$:$1$ rather than as $2001$:db$8$:$0$:$0$:$1$::$1.$

Hexadecimal digits are expressed as lower$-$case letters. For example, $2001$:db$8$::$1$ is preferred

over $2001$:DB$8$::$1.$

are reduced to ::$1$ and ::$,$ respectively.