Which HTTP header is used to distinguish virtual hosts when multiple domain names share a single IP address?

• A. Host
• B. Accept
• C. User-Agent
• D. Referer

Answer: (A)

The ability to serve multiple domain names from one IP hinges on the Host header in HTTP requests. When a client requests a page, it includes the Host header with the domain it’s trying to reach. The server uses that value to pick the correct virtual host configuration and return the content for the right site. This is essential for name-based virtual hosting, where many domains point to the same IP.

Other headers have different roles: Accept specifies the content types the client can handle, User-Agent identifies the client software, and Referer indicates the page that linked to the requested resource. None of these determine which virtual host the request should be served from. So the Host header is the key mechanism for distinguishing virtual hosts.