Nmap is the correct tool in this scenario because it is designed to conduct network discovery and security auditing. It can be used to scan for open ports and identify the services running on those ports along with their version information, which can help to discover known vulnerabilities. Exploit DB is a repository of known exploits and would not be used to identify what services are running. Wireshark is primarily a network protocol analyzer and would not specifically identify services based on open ports. Metasploit is an exploitation framework used after the identification of vulnerabilities, not for the initial discovery of services.