Which statement correctly describes a characteristic of IPv6 unicast addressing?

Introduction / Context:
This question examines your understanding of IPv6 addressing rules, focusing specifically on unicast address ranges. Knowing how to recognize global unicast, link local, and multicast prefixes is essential for designing, configuring, and troubleshooting IPv6 networks. Many exam questions present several plausible looking prefixes, so you must be able to distinguish the correct ones from distractors.

Given Data / Assumptions:
- We are concerned with IPv6 unicast addressing, which identifies a single interface on a network.
- One option references global unicast addresses starting at 2000::/3.
- Other options mention link local prefixes and loopback or multicast semantics.
- Only one statement must be correct, and the rest must contain inaccuracies about IPv6 addressing ranges or usage.

Concept / Approach:
In IPv6, global unicast addresses that are routable on the public Internet are commonly assigned from the 2000::/3 block, which covers addresses from 2000:: up to 3FFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF. Link local addresses, which are used only on a single link for neighbor discovery and similar tasks, are assigned from FE80::/10. Multicast addresses start with FF00::/8. The loopback address is ::1, not the all zero address. Any statement that deviates from these facts is incorrect.

Step-by-Step Solution:
Step 1: Recall that global unicast addresses use the 2000::/3 range, so any statement that matches this is likely to be correct.Step 2: Remember that link local addresses start with FE80::/10, not FF00::/10 or FE00::/12.Step 3: Verify that the unique loopback address is ::1, which is a single address and not expressed as 0000::0 in typical notation.Step 4: Recognize that multicast addresses start with FF00::/8, not FE80::/10.Step 5: Based on these facts, identify the statement about global unicast addresses using the 2000::/3 prefix as the only correct choice.

Verification / Alternative check:
You can cross check the ranges by recalling how IPv6 addressing is often taught. Global unicast is described as IPv6 equivalent of public IPv4 addresses and diagrams usually show 2000::/3 with a variety of current allocations inside. Link local addresses always begin with FE80 and are automatically configured on interfaces. Multicast examples such as FF02::1 and FF02::2 clearly show the FF prefix. The loopback address ::1 appears frequently in examples and documentation and is easy to remember as the IPv6 counterpart of 127.0.0.1.

Why Other Options Are Wrong:
The claim that link local addresses start with FF00::/10 is wrong because that range is reserved for multicast, not unicast. Saying that link local addresses start with FE00::/12 is also incorrect because the used subset is specifically FE80::/10. The statement that the loopback address is 0000::0 is wrong because the loopback is ::1. Finally, the assertion that multicast addresses start with FE80::/10 confuses link local addressing with multicast addressing.

Common Pitfalls:
Students frequently confuse the FE80::/10 link local prefix with global unicast or multicast addresses because all three share the hex digit F. Another common error is to mix up the various sparse allocations that IPv6 documentation uses for examples. Memorizing the main ranges 2000::/3 for global unicast, FE80::/10 for link local, FF00::/8 for multicast, and ::1 for loopback helps avoid these mistakes in both exams and practice.

Final Answer:
The correct statement is that global unicast IPv6 addresses are allocated from the 2000::/3 prefix block.