When multiple domain names (e.g.,www.ironman.com andwww.hulk.com ) resolve to the same IP address (e.g., 1.3.3.7), a web server hosting multiple applications on that IP must determine which application to serve. This is achieved using theHTTP "Host" header, which is part of the HTTP/1.1 protocol. The client (browser) includes the requested domain (e.g., Host: www.ironman.com) in the request, allowing the server to route the request to the appropriate virtual host or application configured for that domain. This is a standard practice in virtual hosting.

Option A ("The web server inspects the HTTP 'Host' header sent by the client"): Correct, as the Host header enables the server to distinguish between applications on the same IP.

Option B ("The web server inspects the cookies sent by the client"): Incorrect, as cookies are used for session management or personalization, not for identifying the requested application.

Option C ("The web server inspects the client's SSL certificate"): Incorrect, as SSL certificates are used for encryption and authentication, not for application routing (though they may include the domain name for validation).

Option D ("The web server uses a reverse DNS lookup of the client's IP address"): Incorrect, as reverse DNS lookup resolves an IP to a domain, which is irrelevant for the server determining the requested application.

The correct answer is A, aligning with the CAP syllabus under "Web Server Configuration" and "HTTP Protocol Security."References: SecOps Group CAP Documents - "HTTP Headers," "Virtual Hosting," and "OWASP Web Security Testing Guide" sections.