The security engineer receives an incident ticket from the helpdesk stating that DNS lookup requests are no longer working from the office. The network team has ensured that Layer 2 and Layer 3…

PING uses ICMP echo requests to test Layer 3 reachability and provides no information about whether any specific TCP or UDP port is open.

Nessus is a vulnerability scanner used for detecting security weaknesses, not a targeted tool for quickly verifying a single port's listening state.

NSLOOKUP sends actual DNS queries and reports resolution results, but it cannot confirm whether the DNS daemon is listening on port 53 if the service is unresponsive or misconfigured.

NMAP is a network port scanner that can probe a target host to determine which ports are open and which services are listening on them. Running a command such as 'nmap -p 53 <dns-server>' directly confirms whether the DNS service is bound to port 53, which is exactly what the scenario requires. No other tool listed can report on port-level listening state.