SLAAC and EUI-64 IPv6 Address Assignment on an Interface

200-301 By islever Editorial Last updated

Configure and verify IPv6 addressing and prefix Describe IPv6 address types

Short answer

C Enable SLAAC on the interface so the router can use the modified EUI-64 process to derive the global unicast IPv6 address from the interface's MAC address.

Question

Which action must be taken to assign a global unicast IPv6 address on an interface that is derived from the MAC address of that interface?
  1. explicitly assign a link-local address
  2. disable the EUI-64 bit process
  3. enable SLAAC on an interface Correct Answer
  4. configure a stateful DHCPv6 server on the network

Key Takeaways

The question tests how a MAC-derived (EUI-64) interface ID is created: SLAAC performs it, so the trap is thinking you must manually assign a link-local address or disable EUI-64, which does the opposite of what is asked.

On a Cisco router interface, an IPv6 global unicast address built from the interface MAC address via the modified EUI-64 process is produced only when Stateless Address Autoconfiguration (SLAAC) is running. This page establishes that enabling IPv6 SLAAC on the interface (typically after an RA is received from a router) is the required action, and explains why the other options cannot generate a MAC-derived global address.

Common mistake: Many learners pick B, believing the EUI-64 bit process must be enabled or toggled — but the option says DISABLE, which would prevent the MAC-based interface ID from being formed, defeating the very mechanism requested.

Expert Analysis

Why the Answer Is Correct

With SLAAC enabled, an interface uses Router Advertisement prefixes plus the modified EUI-64 process to form a 128-bit global unicast address whose interface ID is derived from the interface's 48-bit MAC address (the U/L bit is flipped and FFFE is inserted in the middle). The Cisco configuration trigger is the ipv6 unicast-routing plus the ipv6 address <prefix>/<length> eui-64 form and the reception of RA messages, all part of SLAAC operation defined in RFC 4862. Without SLAAC (and the associated RA/NSDU behavior), the router has no stateless mechanism to synthesize that MAC-based global address automatically, which is exactly what option C enables.

Why the Other Options Are Wrong

Option A is wrong because an explicitly assigned link-local address (for example ipv6 address fe80::1/64) only creates a link-scope address, not a global unicast address, and it does not use the MAC address at all. Option B is wrong because disabling EUI-64 removes the MAC-to-interface-ID mapping; you would then rely on a randomly generated (RFC 4941 privacy) or manually specified interface ID. Option D is wrong because stateful DHCPv6 delivers addresses from a server's pool with no requirement that the interface ID match the MAC, and it does not use EUI-64; that is DHCPv6 stateful mode, not SLAAC. Option D also involves client request/lease mechanics absent from the MAC-derived scenario described.

Community Comment Notes

Community discussion supports C: ZUMY stated plainly "C is the answer," and dsolaide explained that SLAAC "is specifically used to assign only a global unicast IPv6 address, an IPv6 prefix length, and, optionally, a default router." 7d040c6 gave the decisive reasoning that "The EUI-64 process performs the action required, so disabling it would certainly not achieve the outcome - whereas SLAAC does a similar thing, automatically." ElieAC's confusion about option B is the classic trap this page resolves, and several commenters note that the site's answer keys are occasionally wrong, so learners should verify against Cisco/RFC documentation rather than trusting any single posted answer.

Official Reference

https://www.rfc-editor.org/rfc/rfc4862

This link opens the official vendor documentation in a new tab.

Exam Strategy

On CCNA exam questions, keywords like "derived from the MAC address" always point to SLAAC with modified EUI-64, so choose the option that enables or activates the autoconfiguration process rather than one that disables or manually configures it. Rule out any option mentioning DHCPv6 when the question describes stateless, MAC-based generation.

Frequently Asked Questions

Why is disabling the EUI-64 bit process not the correct action here?

EUI-64 is the very process that builds the interface ID from the MAC address. Disabling it removes the MAC-derived ID, so no MAC-based global unicast address would be created.

Does stateful DHCPv6 ever generate a MAC-derived IPv6 address?

No. Stateful DHCPv6 assigns addresses from a server pool, and the interface ID does not need to match the MAC address, so it does not satisfy the question's requirement.

More 200-301 FAQ →

Discussion 24 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 24

  1. maw619 👍 114
    The more people agreeing with the answer helps me sleep better at night.
  2. Brocolee 👍 38
    For anyone that read @dave1992 comment, don't worry! The reason people doing it is because there is a lot of INCORRECT answer especially from #423 - #1057 ( I haven't check anything after that yet). So the more people COMMENTING it, the more it help others validate the answer so when you sit on the actual exam you know you got it right. this user @dave1992 here is just being a Smart As*. the saying goes: if you can't contribute positively, then just shut the F up.
  3. GangsterDady 👍 35
    they leave correct answer comment cause some question's answers on this website are wrong.
  4. ciscodj 👍 31
    you must be new to these types of questions and answers. The reason it's done is because some answers can be incorrect and the more ppl input you get a better idea if the answer is valid or not.
  5. dave1992 👍 28
    i love how you can literally click for the correct answer but theres still people that come here and leave a comment saying," C is the correct answer"
Show 19 more comments
  1. ZUMY 👍 13
    C is the answer
  2. Scalibur 👍 5
    Also, if you see different answers from different people, you will try to research, investigate, and then give a good opinion and feedback to everyone interested in the question!!!!!
  3. dsolaide 👍 3 Answered C
    SLAAC is designed to be a simple, automatic approach to assigning IPv6 addresses. It is defined in RFC4862 and is specifically used to assign only a global unicast IPv6 address, an IPv6 prefix length, and, optionally, a default router.
  4. 7d040c6 👍 2
    The EUI-64 process performs the action required, so disabling it would certainly not achieve the outcome - whereas SLAAC does a similar thing, automatically, so it is the only possible correct answer.
  5. ElieAC 👍 2
    So how do we know the actual correct answer now? because i thought B is the Correct answer, and it made sense for me. Can someone Clarify?
  6. Da_Costa 👍 2
    Enable Stateless Address Auto-Configuration (SLAAC)
  7. MD100MD101FUCKER 👍 2
    Correct Answer: C
  8. oranjo 👍 1
    By default, when generating an IPv6 address from a MAC address, the EUI-64 process is used. This process involves taking the 48-bit MAC address and inserting "FFFE" in the middle, resulting in a 64-bit interface identifier. However, this method can potentially compromise privacy, as the MAC address can be easily traced back to the device.
  9. syougun200x 👍 1
    Thanks for the comment. Followed the below Cisco article and other no Ciscos but could not gererate a global address automatically. I will stopped there cause fixation doesnt help. IPv6 Stateless Autoconfiguration https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipv6_basic/configuration/xe-3se/5700/ip6-statlss-auto-xe.html
  10. ciscopue 👍 1
    B. Disable the EUI-64 bit process. The EUI-64 process automatically modifies the interface identifier portion of the IPv6 address based on the MAC address. By disabling the EUI-64 process, you can use other methods for generating the interface identifier, such as manual configuration or DHCPv6.
  11. EmmySploit 👍 1 Answered D
    This question does go over my head a little bit because A & B are clearly not correct due to the fact that manually configuring ipv6 does not make it global/public ip the same goes for disabling the EUI-64 but SLAAC that is used to automatically assign ip is the answer someone pls help?
  12. TOTO1914 👍 1 Answered C
    SLAAC (Stateless Address Autoconfiguration) allows an IPv6 host/interface to automatically generate a global unicast IPv6 address. When EUI-64 is used, the interface ID can be derived from the interface's MAC address
  13. Geosh 👍 1
    this was my answer too. Thanks 7d for the clarification!
  14. oranjo 👍 1
    Correct answer is B
  15. Crazey 👍 1
    Repeating question
  16. jat1 👍 1 Answered C
    Answer is the C.
  17. rhylos 👍 1 Answered C
    C is correct.
  18. 2b081f1 👍 1 Answered C
    c is correct
  19. Nicocisco 👍 1 Answered C
    C is right

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