Courseiva
← 200-301
Full test
hardmultiple choiceObjective-mapped

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?

Question 1hardmultiple choice
Full question →

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?

Full question →

Answer choices

Why each option matters

Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.

A

Best answer

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

This is correct because EUI-64 is used to derive the host/interface portion of the address.

B

Distractor review

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

This is wrong because EUI-64 does not alter the network prefix length.

C

Distractor review

It replaces the need for a link-local address.

This is wrong because link-local addresses are still a normal and important part of IPv6.

D

Distractor review

It encrypts IPv6 traffic between neighbors.

This is wrong because EUI-64 is an addressing method, not an encryption feature.

Common exam trap

Common exam trap: answer the scenario, not the keyword

A frequent exam trap is assuming that EUI-64 changes the IPv6 prefix length or replaces link-local addresses. Some candidates mistakenly believe EUI-64 modifies the network portion or provides encryption. However, EUI-64 only generates the interface ID from the MAC address and does not affect the /64 prefix or routing. Confusing EUI-64 with link-local address functionality or security features leads to incorrect answers. Understanding that EUI-64 strictly automates the host portion of the IPv6 address helps avoid this pitfall.

Technical deep dive

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.

Related practice questions

Related 200-301 practice-question pages

Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.

CCNA subnetting practice questions

Practise IPv4 subnetting, CIDR, masks, host ranges and subnet selection.

CCNA OSPF practice questions

Practise OSPF neighbours, router IDs, metrics, areas and routing-table interpretation.

CCNA VLAN practice questions

Practise VLANs, access ports, trunks, allowed VLANs and switching scenarios.

CCNA STP practice questions

Practise spanning tree, root bridge election, port roles and STP troubleshooting.

CCNA EtherChannel practice questions

Practise LACP, PAgP, port-channel behaviour and bundle requirements.

CCNA ACL practice questions

Practise standard and extended ACLs, permit/deny logic and traffic filtering.

CCNA NAT practice questions

Practise static NAT, dynamic NAT, PAT and inside/outside address translation.

CCNA DHCP practice questions

Practise DHCP scopes, relay, leases and troubleshooting.

CCNA show ip route practice questions

Practise routing-table output, longest-prefix match, AD and route selection.

CCNA show interfaces trunk practice questions

Practise trunk verification and VLAN forwarding across switches.

CCNA wireless security practice questions

Practise WLAN security, authentication and wireless architecture concepts.

CCNA IPv6 practice questions

Practise IPv6 addressing, routes, neighbour discovery and common IPv6 exam traps.

More questions from this exam

Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.

Question 1

A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?

Question 2

A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?

Question 3

What is the OSPF metric called?

Question 4

A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?

Question 5

A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?

Question 6

A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?

FAQ

Questions learners often ask

What does this 200-301 question test?

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?

Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.

Discussion

Loading comments…

Sign in to join the discussion.