all-zero fields is replaced with two colons (::). If the address contains multiple runs of all-zero fields of the same size, to prevent ambiguities, it is the leftmost that is compressed. For example, is rendered as rather than as . :: is not used to represent just a single all-zero field. For example, is shortened to , but is rendered as .

These methods can lead to very short representations for IPv6 addresses. For example, the localhost (loopback) address, , and the IPv6 unspecified address, ,