mediumMultiple Choice
DHCPv6 Stateful: Configuring managed-config-flag
Router R4 has the following DHCPv6 configuration:
ipv6 dhcp pool DHCP6_POOL2 address prefix 2001:db8:2::/64 dns-server 2001:db8::1 !
interface GigabitEthernet0/1
ipv6 address 2001:db8:2::1/64 ipv6 dhcp server DHCP6_POOL2 ipv6 nd managed-config-flag
no shutdown
What is the effect of this configuration?
Quick Answer
The answer is that hosts will use DHCPv6 to obtain both their IPv6 address and other configuration parameters like DNS. This is correct because the `ipv6 nd managed-config-flag` command sets the Managed Address Configuration flag (M flag) to 1 in Router Advertisement messages, instructing hosts to use stateful DHCPv6 rather than SLAAC for address assignment. Since the DHCPv6 pool also provides a DNS server, the configuration implements DHCPv6 stateful with managed config flag, meaning DHCPv6 handles both addressing and additional parameters. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding of IPv6 address assignment methods and the distinction between the M flag (managed) and O flag (other configuration). A common trap is confusing the M flag with SLAAC—remember that M=1 means "Managed by DHCPv6" for addresses, while the O flag only requests other config. Memory tip: "M for Mandatory DHCP" for addresses, "O for Optional extras."
⚠ Common exam trap
Cisco often tests the distinction between the M flag (managed-config-flag) and the O flag (other-config-flag), where candidates mistakenly think the M flag only affects DNS or that SLAAC is still used for addressing when the M flag is set.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Hosts will use DHCPv6 to obtain both their IPv6 address and other configuration parameters like DNS.
The configuration uses the `ipv6 nd managed-config-flag` command, which sets the Managed Address Configuration flag (M flag) in Router Advertisement (RA) messages. When the M flag is set to 1, hosts are instructed to use DHCPv6 (stateful DHCPv6) to obtain their IPv6 addresses, not SLAAC. Additionally, the DHCPv6 pool provides DNS server information, so hosts will use DHCPv6 for both addressing and other configuration parameters like DNS. This matches option A.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Hosts will use DHCPv6 to obtain both their IPv6 address and other configuration parameters like DNS.
Why this is correct
The managed-config-flag in Router Advertisements tells hosts to use DHCPv6 for addressing, and the pool supplies both a prefix from 2001:db8:2::/64 and the DNS server, so hosts obtain address and configuration parameters via DHCPv6 rather than SLAAC.
- ✗
Hosts will use SLAAC for addressing and DHCPv6 for DNS only.
Why it's wrong here
The managed-config-flag instructs hosts to obtain addresses via DHCPv6 stateful autoconfiguration, not SLAAC; the pool's address prefix confirms stateful addressing is intended. SLAAC with stateless DHCPv6 for DNS only requires the other-config-flag instead, which is the scenario where this option would hold.
- ✗
The DHCPv6 pool is missing a domain-name, so it will not provide any configuration.
Why it's wrong here
A domain-name is optional in a DHCPv6 pool; its absence does not prevent the pool from supplying the configured address prefix and DNS server. Domain-name is only needed when hosts must resolve unqualified names via a specific suffix, which this stem does not require.
- ✗
The ipv6 nd managed-config-flag command is incompatible with the DHCPv6 server and will cause an error.
Why it's wrong here
The managed-config-flag is designed to work alongside a DHCPv6 server, signalling hosts to use stateful DHCPv6 for addressing; it raises no error. It would be the correct pairing whenever stateful DHCPv6 addressing is intended, as the address prefix here indicates.
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Same concept, more angles
1 more way this is tested on 300-410
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An engineer is troubleshooting a DHCPv6 stateful (DHCPv6) deployment. The router is configured as a DHCPv6 server with a pool for prefix 2001:db8:2::/64. Clients on the LAN are configured to use DHCPv6, but they are not receiving IPv6 addresses. The router interface has 'ipv6 address 2001:db8:2::1/64' and 'ipv6 dhcp server DHCP_POOL'. The engineer sees that the clients are sending SOLICIT messages, but the router sends no REPLY. What is the issue?
hard- A.The interface is missing the 'ipv6 nd managed-config-flag' command.
- ✓ B.The DHCPv6 pool is missing the 'address prefix 2001:db8:2::/64' command.
- C.The router needs the 'ipv6 dhcp relay' command on the interface.
- D.The 'ipv6 unicast-routing' command is missing globally.
Why B: The DHCPv6 server pool must be configured with the address prefix that matches the interface's subnet. Without the 'address prefix 2001:db8:2::/64' command in the pool, the server has no addresses to assign, so it cannot respond to SOLICIT messages with an ADVERTISE. The interface configuration alone does not define the pool's address range.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.