N10-009 Question 137
Single answerIPv6 addressing: Mitigating address exhaustion, Compatibility requirements (Tunneling, Dual stack, NAT64)A company has run out of available IPv4 addresses for new client devices. The network team enables IPv6 on the internal LAN so new workstations can receive native IPv6 addresses, but most public websites and several cloud services the company uses are still reachable only over IPv4. Management wants a solution that lets the new IPv6-only clients access those IPv4-only external resources without requiring every internal host to run both protocols. Which solution best meets this requirement?
- A
Deploy dual stack on all client devices so they can use IPv4 and IPv6 simultaneously
- B
Implement NAT64 with DNS64 at the network edge to translate IPv6 client traffic to IPv4 destinations
- C
Configure an IPv6-over-IPv4 tunneling protocol between internal clients and the internet
- D
Use APIPA addressing for clients that cannot obtain an IPv4 address
Show answer and explanation
Correct answer: B
Explanation
The best answer is NAT64 with DNS64 because the company wants to mitigate IPv4 address exhaustion by deploying IPv6-only clients internally while still maintaining compatibility with IPv4-only external services. Dual stack is often recommended during IPv6 transition because it provides broad compatibility, but it does not satisfy the requirement to avoid running both protocols on every endpoint. Tunneling is useful when IPv6 traffic must traverse an IPv4-only portion of the network, but it is not a translation mechanism for reaching IPv4-only application endpoints. NAT64 specifically addresses communication from IPv6-only hosts to IPv4-only servers, and DNS64 complements it by synthesizing AAAA responses when only A records exist. This aligns with common IPv6 transition guidance from standards bodies such as the IETF, including RFC 6146 for Stateful NAT64 and RFC 6147 for DNS64.
- A. Incorrect.
This is incorrect because dual stack requires each client to run both IPv4 and IPv6. While dual stack is a common transition strategy, the scenario specifically states the company wants IPv6-only clients to reach IPv4-only external resources without requiring every host to run both protocols. Dual stack would also still consume IPv4 addresses on clients, which does not best address IPv4 exhaustion.
- B. Correct.
This is correct. NAT64 is designed to allow IPv6-only clients to communicate with IPv4-only servers by translating between IPv6 and IPv4 at a gateway. DNS64 is typically paired with NAT64 so that when an IPv6-only client queries DNS for an IPv4-only host, the DNS server can synthesize an AAAA record from the A record. This approach preserves IPv6-only addressing on internal clients while still providing access to legacy IPv4 internet resources.
- C. Incorrect.
This is incorrect because tunneling is generally used to carry one protocol through another network, such as transporting IPv6 traffic across an IPv4 infrastructure. It does not by itself solve the problem of IPv6-only clients needing to communicate with IPv4-only destinations. Tunneling preserves the original protocol rather than translating between IPv6 and IPv4.
- D. Incorrect.
This is incorrect because APIPA is a link-local IPv4 addressing mechanism in the 169.254.0.0/16 range used when a host cannot obtain an IPv4 address from DHCP. It does not provide routed internet connectivity and does not address IPv6-to-IPv4 communication requirements. Choosing this option reflects a misconception that any automatic address assignment can solve address exhaustion.