CCNA Network Infrastructure and Connectivity Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  It automatically creates the interface ID portion of the IPv6 address from the MAC address.

  Why this is correct

  EUI-64 is the interface ID generation method used when a router interface has no explicit 64-bit host portion configured. The 48-bit MAC address is split, the hex value FFFE is inserted between the OUI and the serial number, and the universal/local bit is flipped to form the 64-bit interface identifier. This automatically completes the IPv6 address and is why the statement is correct.

• ✗

  It changes the /64 prefix into a /48 prefix for summarization.

  Why it's wrong here

  EUI-64 operates exclusively on the interface ID (the low-order 64 bits) of the IPv6 address; it has no mechanism to alter the network prefix or its length. The /64 is the subnet prefix and is configured independently by the network administrator, often for routing and summarization planning. Changing a /64 to a /48 would require a separate renumbering or aggregation configuration, not an automatic process, making this option incorrect.

  When this WOULD be correct

  In a different question, if it asked about IPv6 address summarization techniques, and it provided a scenario where a network administrator needs to summarize multiple /64 prefixes into a single /48 prefix for routing efficiency, then this option would be correct.

• ✗

  It replaces the need for a link-local address.

  Why it's wrong here

  Every IPv6 interface is required to have a link-local address (fe80::/10) for Neighbor Discovery, duplicate address detection, and many routing protocol operations such as OSPFv3. EUI-64 can be used to generate the interface ID for a link-local address, but it in no way removes the need for that address. Even when a global unicast address is configured, the link-local address remains active and essential, so this option is false.

  When this WOULD be correct

  In a different question setup, if the question asked about a technology that eliminates the need for link-local addresses in specific scenarios, such as a proprietary protocol that uses a different addressing scheme, then this option could be correct.

• ✗

  It encrypts IPv6 traffic between neighbors.

  Why it's wrong here

  EUI-64 is purely a deterministic method for generating a 64-bit interface identifier from a MAC address, involving bit manipulation and insertion of FFFE. It performs no cryptographic operations and provides no confidentiality or integrity for transmitted data. IPv6 traffic encryption is handled by IPsec (AH or ESP headers), which is a separate security framework unrelated to address assignment, thus this option is incorrect.

  When this WOULD be correct

  In a different question that asks about the security features of IPv6 protocols, if it specifically inquires about methods to secure communications between neighboring devices, then the option could be correct if discussing encryption mechanisms like IPsec, which can be used in conjunction with IPv6.

Option-by-option analysis

Why each answer is right or wrong

Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.

Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”

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