Why a Proxy That Works at Home May Fail on a VPS: The Source-IP Check

A proxy configuration that works from a home computer can stop working after moving the application to a VPS, even though the hostname, port and code are unchanged. When the endpoint uses IP authentication, the provider checks the public source address of the machine connecting to the proxy, not the proxy's exit address. The article's illustrative example shows a home address on the allowlist being accepted while a VPS address is rejected, and notes that adding the exit IP would not fix this. Recommended steps include confirming the endpoint uses IP authentication, determining the real outbound address from the application's host, and accounting for NAT gateways, VPNs, or IPv4/IPv6 differences. Checking the source through the proxy itself reports the exit IP and can be misleading, so provider logs or controlled tests are suggested instead.