N10-009 Question 233
Select 2Zone types: Forward, Reverse, Authoritative vs. non-authoritative, Primary vs. secondary, Recursive, Hosts fileA company is migrating a public web application to a new IP address. During testing, users on the internal network can browse to https://portal.example.com and receive the new address, but a security analyst notices that reverse lookups on the new IP still return no hostname. The company also wants to ensure that if the primary DNS server for example.com fails, another DNS server can continue answering with a copy of the zone data. Which TWO actions should the network administrator take to meet these requirements?
- A
Create or update a PTR record in the appropriate reverse lookup zone for the new IP address
- B
Add an entry to the hosts file on the administrator's workstation so all clients can resolve the new address
- C
Configure a secondary zone for example.com on another DNS server
- D
Enable recursive queries on the authoritative public DNS server so it can generate reverse records automatically
- E
Create a non-authoritative copy of the zone on a resolver-only DNS server and use it as the failover server
Show answer and explanation
Correct answers: A, C
Explanation
This scenario tests practical DNS administration across several related concepts. A forward lookup zone maps hostnames to IP addresses using records such as A and AAAA, while a reverse lookup zone maps IP addresses back to hostnames using PTR records. Because the analyst specifically observed failed reverse lookups, the required fix is to add or update the PTR record in the reverse zone. For resilience, the administrator should configure a secondary zone on another DNS server. A secondary zone receives zone transfers from the primary and can answer authoritatively if the primary is unavailable. By contrast, a hosts file is only local to one machine and does not scale or support network-wide DNS management. Also, recursion is a query behavior, not a mechanism for creating reverse records or replacing authoritative zone hosting. These distinctions align with standard DNS operational practices and with vendor documentation from Microsoft DNS, BIND administration guides, and general DNS standards described in RFC 1034 and RFC 1035.
- A. Correct.
Correct. Forward lookups such as portal.example.com to an IP address use A or AAAA records in a forward lookup zone, but reverse lookups from IP address to hostname require a PTR record in the appropriate reverse lookup zone, such as an in-addr.arpa zone for IPv4. If reverse lookups are failing after the migration, adding or updating the PTR record is the proper fix.
- B. Incorrect.
Incorrect. A hosts file entry affects only the local system where it is configured. It does not update DNS for other clients, does not provide reverse lookup capability for the network, and is not an appropriate enterprise solution for a public application migration. This is a common misconception because hosts files can override name resolution locally, but they are not a substitute for DNS zone records.
- C. Correct.
Correct. A secondary zone is a read-only copy of a primary zone transferred from the primary DNS server. If the primary server becomes unavailable, the secondary server can continue answering authoritatively for that zone using the replicated data. This directly addresses the availability requirement for example.com.
- D. Incorrect.
Incorrect. Recursive queries allow a DNS server to query other DNS servers on behalf of a client to find an answer, but recursion does not create DNS records and does not automatically generate PTR records. Public authoritative DNS servers are commonly configured to answer authoritatively for their zones and often do not need recursion enabled at all.
- E. Incorrect.
Incorrect. A resolver-only server that provides cached answers is not hosting an authoritative copy of the company's zone. Cached or non-authoritative data cannot reliably serve as the authoritative failover source for example.com. To meet the requirement, the backup server must host the zone as a secondary and answer authoritatively for it.