Which of the following is a link-local unicast address?

A link-local unicast address is defined for use within a single local network segment and is not routable beyond that segment. In IPv6, link-local addresses begin with the prefix FE80::/10. This means that any address starting with FE80 to FEBF is considered a link-local unicast address.

The choice of FE80::1 falls squarely within this range, making it the correct answer. It can be used by network interfaces on the same local segment to communicate without the need for a global address or external routing.

In contrast, the address 2001:db8::1 is an example of a global unicast address typically used for documentation and should be routable. FC00::1 is an address that belongs to the Unique Local Address (ULA) range, which is intended for local communications within a site and can be routable within that site but not on the global Internet. FF02::1, on the other hand, is a multicast address intended for multicast communications, specifically for all nodes on the local link.

These distinctions clarify why FE80::1 is the only option that qualifies as a link-local unicast address.