What does the client do to automatically detect proxy settings?

The process of automatically detecting proxy settings primarily involves utilizing the Web Proxy Auto-Discovery Protocol (WPAD). When a client is configured to find proxy settings automatically, it leverages WPAD by sending a request to discover proxy configurations via DHCP or DNS. This method allows the client to receive the necessary proxy information without requiring user intervention, ensuring that it can connect to the internet through the appropriate proxy server seamlessly.

In contrast, manually looking up proxies or checking local configurations would not provide an automated detection method and would require user input or pre-existing information on the client device. Sending an IP packet to discover proxies is also not part of the standard proxy detection process. Therefore, using WPAD is the most efficient and effective means for automatic proxy configuration detection.