Cisco CCNA (200-301)Network FundamentalsMedium
An engineer is documenting IPv6 addresses used on an internal network that must be routable only within the organization and never forwarded to the internet, similar in purpose to RFC 1918 private addresses. Which address best fits this description?
- AFF02::1
- BFE80::215:5DFF:FE00:2
- C2001:DB8::1
- DFD12:3456:789A:1::1
Show answer & explanationAnswer & explanation
Correct answer: D. FD12:3456:789A:1::1
Unique Local Addresses (ULA) use the FC00::/7 range, with the locally assigned FD00::/8 prefix being the practical form used in production. They are meant for internal routing only, similar to RFC 1918 private IPv4 space.
Why the other options are wrong
- A. FF02::1 is a multicast address for all nodes on the local link, not a unicast internal address.
- B. FE80::/10 is a link-local address, valid only on the local link, not routed at all.
- C. 2001:DB8::/32 is reserved strictly for documentation and examples, not for real internal networks.
Unique Local Address (ULA)
An IPv6 address type in the FC00::/7 block (commonly FD00::/8) used for private, internal-only routing, analogous to IPv4 private addressing.
- Range: FC00::/7, practical use FD00::/8
- Not routable on the public internet
- Different from link-local (FE80::/10) which is not routed at all
Memory trick: FD is Family and friends Domain—stay inside the house.