Identify the link-local address from the following IPv6 addresses:
2023
Identify the link-local address from the following IPv6 addresses:
- A.
2001:0db8:abcd:0012:0000:0000:0000:0001
- B.
FE80:0000:0000:0000:0202:B3FF:FE1E:8329
- C.
FF02:0000:0000:0000:0000:0000:0000:0001
- D.
::1
- E.
2001:4860:4860::8888
Attempted by 10 students.
Show answer & explanation
Correct answer: B
Concept
An IPv6 address is classified by the leading bits of its first hextet, which fix its scope and purpose. A link-local unicast address is valid only on a single network link (it is never routed off that link), and by RFC 4291 it lies in the FE80::/10 block. The /10 pins only the first 10 bits to 1111111010, so its first hextet ranges from FE80 to FEBF. The task is to match each address to its reserved prefix and pick the one whose high-order bits fall in that link-local range.
Applying the prefix rules
Address (first hextet) | Reserved prefix | Type / scope |
|---|---|---|
|
| Documentation / global |
|
| Link-local unicast |
|
| Multicast |
|
| Loopback |
|
| Global unicast |
Only the address whose first hextet is FE80 has high-order bits inside FE80::/10, so it is the link-local address.
Cross-check
Expand the first hextet to bits: FE80 = 1111 1110 1000 0000. Its first 10 bits are 1111111010, which is exactly the FE80::/10 pattern (any first hextet FE80-FEBF shares these 10 bits). None of the other addresses' high-order bits match this pattern, confirming the choice.