N10-009 Question 226
Single answer3.4 Given a scenario, implement IPv4 and IPv6 network services.A company has enabled IPv6 on a new branch office LAN, but hosts are still receiving only link-local IPv6 addresses and cannot reach internal IPv6 application servers at the main office. The network technician confirms that the router interface connected to the LAN has a valid global unicast IPv6 address configured. Management wants hosts to automatically receive IPv6 addresses and the correct default gateway without manually configuring each endpoint. Which action should the technician take FIRST to meet this requirement?
- A
Configure and enable IPv6 router advertisements on the LAN interface
- B
Create an AAAA record for each client in the DNS server
- C
Enable APIPA on the clients so they can self-assign routable addresses
- D
Configure a DHCPv4 scope with option 003 for the default gateway
Show answer and explanation
Correct answer: A
Explanation
This scenario tests implementation of IPv6 network services, specifically automatic address configuration and gateway discovery. In a normal IPv6 deployment, hosts automatically create a link-local address, but they need Router Advertisements from a local router to learn the on-link prefix and default gateway. With SLAAC, the host can then generate its own global unicast address from the advertised prefix. Even when DHCPv6 is used for additional settings, the default gateway is still learned through RAs rather than DHCPv6. This behavior is defined in IPv6 Neighbor Discovery and Stateless Address Autoconfiguration standards, including RFC 4861 and RFC 4862. Therefore, the first and most appropriate action is to ensure IPv6 router advertisements are configured and enabled on the LAN interface.
- A. Correct.
Correct. In IPv6, hosts typically learn the default gateway through Router Advertisements (RAs) sent by a router as part of Neighbor Discovery. RAs can also support Stateless Address Autoconfiguration (SLAAC), allowing hosts to automatically generate usable IPv6 addresses from the advertised prefix. If clients are receiving only link-local addresses, a common issue is that RAs are not being sent or are not reaching the LAN.
- B. Incorrect.
Incorrect. AAAA records map hostnames to IPv6 addresses in DNS, but they do not assign IPv6 addresses to clients or provide a default gateway. A technician might choose this if they confuse name resolution with address assignment.
- C. Incorrect.
Incorrect. APIPA is an IPv4 feature that assigns addresses in the 169.254.0.0/16 range when DHCP is unavailable. It does not apply to IPv6 routable addressing. In IPv6, link-local addressing is automatic, but link-local addresses alone are not sufficient for routed access to remote IPv6 networks.
- D. Incorrect.
Incorrect. DHCPv4 scope option 003 provides the default gateway for IPv4 clients only. It has no effect on IPv6 addressing or IPv6 default gateway assignment. In IPv6, the default gateway is normally learned through Router Advertisements, not DHCPv6.