> For the complete documentation index, see [llms.txt](https://help.gpmloginapp.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.gpmloginapp.com/gpm-login-global-en/getting-started/understanding-fingerprints/tcp-ip-fingerprint.md). # TCP/IP Fingerprint This is a relatively effective method to detect whether a user is using a proxy or not. This method relies on the characteristics of the received packets to determine the operating system from which the packet originated. For example, if you are using Windows but the proxy you use is provided by a Linux server (most proxy servers run on Linux), the system will determine that you are using a proxy. The use of a proxy is not prohibited, but it is considered a factor indicating that you might not be a "real" user. The client side (browser/user's machine) cannot handle this issue; instead, the proxy server must modify the outgoing packets to correctly simulate the client's operating system. Therefore, choosing a suitable proxy provider is also a very important factor. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://help.gpmloginapp.com/gpm-login-global-en/getting-started/understanding-fingerprints/tcp-ip-fingerprint.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.