A network engineer wants IPv6 clients to automatically generate their own addresses using router advertisements while also receiving DNS server information without deploying a full stateful DHCPv6 server. Which router configuration accomplishes this?
- AStateful DHCPv6 only, disabling router advertisements entirely
- BNeighbor Discovery Protocol with the A-flag disabled on all interfaces
- CSLAAC with the O-flag set, enabling stateless DHCPv6 for options like DNS
- DSLAAC with the M-flag set, forcing full stateful DHCPv6 address assignment
Show answer & explanationAnswer & explanation
Correct answer: C. SLAAC with the O-flag set, enabling stateless DHCPv6 for options like DNS
When the Other Configuration (O) flag is set in router advertisements, clients use SLAAC to self-generate addresses but still query a stateless DHCPv6 server for supplementary options such as DNS server addresses, without a full stateful DHCPv6 lease process. Setting the M-flag would instead trigger full stateful DHCPv6 address assignment, and disabling the A-flag would prevent SLAAC address generation altogether.
Why the other options are wrong
- A. Disabling router advertisements removes SLAAC capability entirely, contradicting the requirement.
- B. Disabling the A-flag prevents SLAAC address autoconfiguration on the prefix, which is the opposite of what's wanted.
- D. The M-flag forces full stateful DHCPv6, which is more than what's needed here.
SLAAC vs DHCPv6 Flags
IPv6 router advertisements include M (Managed) and O (Other) flags that control whether clients use stateful DHCPv6 for addresses and/or stateless DHCPv6 for extra configuration data like DNS.
- A-flag: enables SLAAC address autoconfiguration on the prefix
- M-flag: triggers full stateful DHCPv6 for address assignment
- O-flag: triggers stateless DHCPv6 just for extra options (e.g., DNS)
Memory trick: O is for 'Other stuff' like DNS, M is for 'Managed' full addressing.