An administrator receives a call from a user reporting that one of the application servers is not accessible by host name but is accessible via an IP address. Which of the following is the MOST…

A misconfigured reverse lookup zone affects PTR records used for IP-to-hostname resolution, not hostname-to-IP forward lookups that end users rely on.

An MX record is used for mail exchange routing and has no bearing on general host name resolution for application servers.

A missing DNS resource record - specifically the A record - means the DNS server has no entry to resolve the hostname to an IP address, causing name resolution to fail. Because the IP address still works directly, the network path and server itself are functional; only the name-to-IP mapping is absent. Adding the correct A record to the appropriate DNS zone would resolve the issue.

If the entire forward lookup zone were missing, no hostname in that domain would resolve at all, which would be a broader outage rather than a single host being unreachable by name.