CCNA Network Infrastructure and Connectivity Practice Question
This 200-301 practice question tests your understanding of network infrastructure and connectivity. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. A key principle to apply: eUI-64 automatically generates the lower 64 bits of an IPv6 address by embedding the device's MAC address into the interface identifier portion.. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A router interface is configured with the prefix 2001:db8:acad:12::/64 and uses EUI-64 to build the interface ID. What is the main purpose of EUI-64 in this context?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
It automatically creates the interface ID portion of the IPv6 address from the MAC address.
EUI-64 is used to automatically generate the interface identifier portion of the IPv6 address from the underlying MAC address. In practical terms, the /64 prefix provides the network portion, and EUI-64 helps derive the lower 64 bits without the administrator manually typing a full host portion. This can make addressing easier in environments where automatic formation is desired.
The important idea is that EUI-64 affects the interface ID, not the prefix length or the routing behavior of the network. It is an address-construction method, not a routing protocol.
Key principle: EUI-64 automatically generates the lower 64 bits of an IPv6 address by embedding the device's MAC address into the interface identifier portion.
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
This is correct because EUI-64 is used to derive the host/interface portion of the address.
Related concept
EUI-64 automatically generates the lower 64 bits of an IPv6 address by embedding the device's MAC address into the interface identifier portion.
✗
It changes the /64 prefix into a /48 prefix for summarization.
Why it's wrong here
This is wrong because EUI-64 does not alter the network prefix length.
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
This is wrong because link-local addresses are still a normal and important part of IPv6.
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
This is wrong because EUI-64 is an addressing method, not an encryption feature.
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.
✓It automatically creates the interface ID portion of the IPv6 address from the MAC address.Correct answer▾
Why this is correct
This is correct because EUI-64 is used to derive the host/interface portion of the address.
✗It changes the /64 prefix into a /48 prefix for summarization.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because EUI-64 does not change the prefix length of an IPv6 address; it is used solely for generating the interface ID from a MAC address within the existing prefix.
★ When this WOULD be the correct answer
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.
Why candidates choose this
Candidates may choose this option due to confusion about IPv6 prefix lengths and summarization concepts, leading them to incorrectly associate EUI-64 with prefix manipulation instead of its actual function in interface ID generation.
✗It replaces the need for a link-local address.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because EUI-64 does not replace the need for a link-local address; link-local addresses are essential for local network communication in IPv6, regardless of how the global address is generated.
★ When this WOULD be the correct answer
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.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of IPv6 addressing concepts, believing that EUI-64's role in generating global addresses might also extend to eliminating the necessity for link-local addresses.
✗It encrypts IPv6 traffic between neighbors.Wrong answer — click to see why▾
Why this is wrong here
This option is wrong because EUI-64 does not encrypt IPv6 traffic; it is used to generate the interface ID from the MAC address, which is unrelated to encryption processes.
★ When this WOULD be the correct answer
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.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of IPv6 security features, confusing the role of EUI-64 with the need for secure communication methods, leading them to associate it with encryption.
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?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Remember, EUI-64 is about address generation, not routing or network configuration. Focus on its role in forming the interface ID.
Detailed technical explanation
How to think about this question
EUI-64 (Extended Unique Identifier-64) is a method used in IPv6 to automatically generate the interface identifier portion of an IPv6 address. This interface ID occupies the lower 64 bits of the 128-bit IPv6 address. The process takes the 48-bit MAC address of the interface, splits it, inserts a fixed 16-bit value (0xFFFE) in the middle, and flips the Universal/Local bit to create a unique 64-bit interface ID. This approach ensures that each interface has a unique identifier derived from its hardware address, simplifying address configuration and reducing human error.
In IPv6, the network prefix is typically a /64, meaning the first 64 bits represent the network portion, and the last 64 bits represent the interface ID. EUI-64 only affects the interface ID portion and does not alter the prefix length or network routing behavior. Cisco routers use EUI-64 to automatically generate the interface ID when configured with a global unicast prefix, such as 2001:db8:acad:12::/64, allowing the router to form a complete IPv6 address without manual input of the host portion.
A common exam trap is confusing EUI-64 with other IPv6 features like link-local addressing or encryption. EUI-64 does not replace link-local addresses, which are always required for IPv6 operation on a link. It also does not provide encryption or security; it is purely an addressing method. Practically, EUI-64 helps network engineers by automating address assignment, but administrators can still manually configure interface IDs if needed for specific addressing schemes.
KKey Concepts to Remember
EUI-64 automatically generates the lower 64 bits of an IPv6 address by embedding the device's MAC address into the interface identifier portion.
IPv6 addressing requires a /64 prefix length to separate the network portion from the interface identifier, which EUI-64 helps construct.
EUI-64 does not modify the IPv6 network prefix length or perform any summarization or routing functions.
Link-local IPv6 addresses are mandatory and separate from global unicast addresses generated using EUI-64.
EUI-64 is an addressing mechanism and does not provide encryption or security features for IPv6 traffic.
Routers and hosts use EUI-64 to simplify IPv6 address configuration by avoiding manual entry of the interface ID.
The interface ID generated by EUI-64 ensures uniqueness on the local link by leveraging the globally unique MAC address.
EUI-64 is commonly used in Cisco devices to automate IPv6 address assignment on router interfaces for consistent addressing.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
EUI-64 automatically generates the lower 64 bits of an IPv6 address by embedding the device's MAC address into the interface identifier portion.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Review eUI-64 automatically generates the lower 64 bits of an IPv6 address by embedding the device's MAC address into the interface identifier portion., then practise related 200-301 questions on the same topic to reinforce the concept.
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — EUI-64 automatically generates the lower 64 bits of an IPv6 address by embedding the device's MAC address into the interface identifier portion..
What is the correct answer to this question?
The correct answer is: It automatically creates the interface ID portion of the IPv6 address from the MAC address. — EUI-64 is used to automatically generate the interface identifier portion of the IPv6 address from the underlying MAC address. In practical terms, the /64 prefix provides the network portion, and EUI-64 helps derive the lower 64 bits without the administrator manually typing a full host portion. This can make addressing easier in environments where automatic formation is desired.
The important idea is that EUI-64 affects the interface ID, not the prefix length or the routing behavior of the network. It is an address-construction method, not a routing protocol.
What should I do if I get this 200-301 question wrong?
Review eUI-64 automatically generates the lower 64 bits of an IPv6 address by embedding the device's MAC address into the interface identifier portion., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
EUI-64 automatically generates the lower 64 bits of an IPv6 address by embedding the device's MAC address into the interface identifier portion.
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