Which prefix is used for IPv6 global unicast addresses?

• A. fe80::/10
• B. ::ffff/96
• C. 2000::/3
• D. ff00::/8

Answer: (C)

Global unicast addresses are the IPv6 addresses intended to be globally routable on the Internet. The prefix allocated for this space is 2000::/3, which spans from 2000:: to 3fff:ffff:ffff:ffff:ffff:ffff:ffff:ffff. This range is designated for publicly reachable addresses, the IPv6 equivalent of the public IPv4 space.

Fe80::/10 covers link-local addresses, which are used only on a single local link and aren’t routable beyond that link. ::ffff/96 represents IPv4-mapped IPv6 addresses used for IPv4-IPv6 interoperability, not global unicast routing. ff00::/8 is the multicast space, consisting of addresses delivered to multiple recipients rather than a single interface. Therefore, the prefix for IPv6 global unicast addresses is 2000::/3.