Which Unicast address scope is publicly accessible with a hierarchical design?

The correct answer, Aggregatable Global, denotes a unicast address scope that is designed for global uniqueness and is publicly accessible. This type of address allows for a hierarchical routing structure, which is essential for efficient routing on the internet. Each Aggregatable Global address can be broken down into regions or organizations, making it easier to manage large networks and improve scalability.

In this addressing scheme, the global routing prefix helps routers identify the network portion of the address, which is crucial for the global propagation of packets across different networks. This hierarchical organization supports efficient routing and reduces the size of routing tables, enhancing overall internet performance.

In contrast, Site-local addresses are intended for use within a specific site or organization and are not routable on the global internet. Similarly, Link-local addresses are meant for communication within a single network segment and also lack global routability. Aggregatable Local addresses, while they imply some local organization, do not carry the same global routing capabilities as Aggregatable Global addresses, which are paramount for widespread public accessibility on the internet.