The 128 bits of an IPv6 address are represented in 8 groups of 16 bits each. Each group is written as four hexadecimal digits and the groups are separated by colons (:). An example of this representation is 2001:0db8:0000:0000:0000:ff00:0042:8329.
For convenience, an IPv6 address may be abbreviated to shorter notations by application of the following rules.
- One or more leading zeroes from any groups of hexadecimal digits are removed; this is usually done to either all or none of the leading zeroes. For example, the group 0042 is converted to 42.
- Consecutive sections of zeroes are replaced with a double colon (::). The double colon may only be used once in an address, as multiple use would render the address indeterminate. RFC 5952 recommends that a double colon must not be used to denote an omitted single section of zeroes.
An example of application of these rules:
- Initial address: 2001:0db8:0000:0000:0000:ff00:0042:8329
- After removing all leading zeroes in each group: 2001:db8:0:0:0:ff00:42:8329
- After omitting consecutive sections of zeroes: 2001:db8::ff00:42:8329