Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
What does a host rely on when using SLAAC to build an IPv6 address?
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
Distractor review
Only a DNS reply
DNS does not provide the Layer 3 prefix needed for SLAAC.
B
Best answer
A Router Advertisement containing the network prefix
Correct. Router Advertisements are central to SLAAC.
C
Distractor review
An ARP reply from the default gateway
ARP is an IPv4 mechanism and not used in IPv6 the same way.
D
Distractor review
A VTP summary advertisement
VTP has nothing to do with IPv6 host addressing.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is assuming that SLAAC depends on DHCP or ARP replies to configure IPv6 addresses. Many candidates mistakenly believe that DHCPv6 or DNS responses provide the necessary prefix information, or that ARP functions similarly in IPv6 as in IPv4. However, SLAAC relies exclusively on ICMPv6 Router Advertisements to deliver network prefix information. Misunderstanding this can lead to incorrect answers, especially when options mention DHCP, DNS, or ARP. Recognizing that Router Advertisements are the sole source of prefix data in SLAAC is essential to avoid this pitfall.
Technical deep dive
How to think about this question
Stateless Address Autoconfiguration (SLAAC) is a fundamental IPv6 feature that allows hosts to self-configure their IP addresses without requiring a DHCP server. The core mechanism involves the host listening for ICMPv6 Router Advertisements (RAs) sent periodically or in response to Router Solicitations. These RAs contain the network prefix and configuration flags that inform the host how to construct its IPv6 address and whether to use additional configuration methods. When a host receives a Router Advertisement, it extracts the advertised network prefix and appends its own interface identifier, typically derived from the MAC address or generated randomly, to form a full IPv6 address. This process eliminates the need for manual configuration or DHCPv6 in many scenarios. Cisco devices and hosts rely on these RAs to ensure proper network prefix assignment and reachability within the IPv6 subnet. A common exam trap is confusing SLAAC with DHCPv6 or IPv4 mechanisms like ARP. Unlike DHCPv6, SLAAC does not require a server to assign addresses; instead, it depends solely on Router Advertisements. Additionally, ARP is not used in IPv6 for address resolution, so expecting an ARP reply for SLAAC is incorrect. Understanding this distinction is crucial for CCNA candidates to avoid misinterpreting how IPv6 addressing works in Cisco environments.
KKey Concepts to Remember
- SLAAC enables IPv6 hosts to autonomously configure their addresses by using network prefix information advertised in ICMPv6 Router Advertisements.
- Router Advertisements contain essential prefix and configuration flags that hosts use to build their IPv6 addresses without requiring DHCPv6 servers.
- IPv6 address autoconfiguration via SLAAC appends a host-generated interface identifier to the prefix learned from Router Advertisements.
- Unlike IPv4, IPv6 does not use ARP for address resolution, so ARP replies are irrelevant to SLAAC and IPv6 address configuration.
- DNS replies do not provide Layer 3 prefix information and therefore cannot be used by hosts to build IPv6 addresses with SLAAC.
- VTP advertisements are unrelated to IPv6 addressing and do not influence SLAAC or host IP configuration.
- Hosts rely solely on ICMPv6 Router Advertisements to learn network prefixes and configuration parameters for SLAAC.
- Misinterpreting DHCPv6 or ARP as part of SLAAC can lead to incorrect conclusions about IPv6 address autoconfiguration.
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.
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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?
SLAAC enables IPv6 hosts to autonomously configure their addresses by using network prefix information advertised in ICMPv6 Router Advertisements.
What is the correct answer to this question?
The correct answer is: A Router Advertisement containing the network prefix — With Stateless Address Autoconfiguration, hosts learn the prefix information from ICMPv6 Router Advertisements and then build their own interface identifier.
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.
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