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Cisco Certified Network Associate (CCNA) · Cisco
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The engineer needs a routable, locally-unique IPv6 unicast address that is not advertised to the internet, which perfectly describes a Unique Local Address (ULA). These fall under the prefix FC00::/7, but in practice, only FD00::/8 is used, making B the correct choice. Option A uses FF00::, which is a multicast address range, not unicast. C uses FE80::, which is a link-local address, valid only on a single link and not routable. D uses FC00::, which is technically part of the ULA block but was reserved for centralized assignment, so FD00:: is the valid and widely accepted form for locally assigned ULAs today.
Option B uses fd00::/64, which is within the ULA range. This address prefix ensures that the network is not supposed to be routed outside of the local network, thus inherently blocking advertisement to the internet. Option D uses fc00::/8, which is also part of the ULA space but includes the full interface ID, making it valid for a local address. However, the address in option B (fd00::/64) is more commonly used and directly aligns with the standard for ULA configuration for privacy and ease of use.
In IPv6, “unique local” addresses (ULAs) are the correct choice for an internal-only, routable address that is not advertised on the global Internet. The ULA space is fc00::/7, which typically shows up as addresses beginning with fc or fd. Among the options given: • ff00::… is a multicast address (not a unicast host address). • fe80::… is a link-local address (only valid on the local link and not routable across subnets). • fc00::… or fd00::… belong to the Unique Local Address space (fc00::/7). These are routable within a site but not globally advertised. Because the question explicitly wants a “locally-unique unicast address that is blocked from being advertised to the internet,” the best-fit ULA is typically in the fd00::/8 range (option B), which is why interface vlan 2000 ipv6 address fd00::1234:2343/64 is the correct solution.