Cisco CCNA (200-301)Network FundamentalsHard
An IPv6 client is configured with the address 2001:DB8:ACAD:1::10/64. Which of the following is a valid link-local address for this host?
- AFC00::1:10
- BFF02::1
- CFE80::1A2B:3CFF:FE4D:5E6F
- D2001:DB8:ACAD:1:FE80::10
Show answer & explanationAnswer & explanation
Correct answer: C. FE80::1A2B:3CFF:FE4D:5E6F
IPv6 link-local addresses always start with FE80::/10. The rest of the address is typically derived from the interface's MAC address using EUI-64 or randomly generated. Option B starts with FE80:: and has a valid EUI-64 derived format (if the MAC was 18:2B:3C:4D:5E:6F), making it a valid example of a link-local address. Options A, C, and D do not begin with the correct FE80:: prefix for link-local addresses.
Why the other options are wrong
- A. FC00::/7 is the prefix for Unique Local Addresses (ULAs), not link-local addresses.
- B. FF02::1 is the all-nodes link-local multicast address, not a host's unique link-local address.
- D. This address uses the global unicast prefix 2001:DB8:ACAD:1, not the link-local prefix FE80::/10.
IPv6 Link-Local Address
An IPv6 link-local address is automatically configured on every IPv6-enabled interface and is used for communication only within the local network segment (link).
- Always starts with the prefix FE80::/10.
- Not routable beyond the local link.
- Used for neighbor discovery, address auto-configuration (SLAAC), and routing protocol updates.
- Often derived from the MAC address using EUI-64 or generated randomly.
Memory trick: Global is world-wide, Link-local is neighbor-friendly, Unique-local is private home.