Cisco Certified Network Associate (CCNA) Practice Exam

What type of IPv6 address is represented by ::/128?

1. Unspecified

2. Loopback

3. Global Unicast

4. Unique Local Address

The correct answer is: Unspecified

The address represented by ::/128 is known as an unspecified address. In the context of IPv6, the unspecified address is denoted by a double colon (::), which represents all zero bits. It is used primarily to indicate the absence of an address, such as when a device has not yet been assigned an address or is seeking to obtain one. This address serves specific purposes, particularly in the initial stages of communication when a device may not have a valid address. For example, it can be used in the source address field of a packet sent by an application that does not yet have an assigned address. The unspecified address cannot be assigned to any interface and is not routable, meaning it is intended strictly for local use within a device. In contrast, the loopback address is a specific IPv6 address (::1) used for loopback testing within a single device, while global unicast addresses and unique local addresses have specific roles in enabling communication across networks and within private networks, respectively.