How to know if a user is using a proxy? [duplicate]

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Detecting whether a user is behind a proxy

Is there a way to know if a user is behind a proxy ?

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No, but if it is for caching purposes you can control the caching of proxies pretty efficiently using the http protocol headers.

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Generally, Piotr Blasiak is right, because we're talking about a Layer 7 protocol, namely HTTP, in which case the proxy acts as a client against the (web-) server. Afaik, the HTTP requests originating from a proxy cannot be distinguisht from those coming from an "actual" client. However, you're able to determine the user's IP address. In most cases this is a useless information. If, however, this IP address belongs to a well known proxy (e.g. one of the tor network), then you're almost sure. So, the only approach is based on probabilistic guesses and lookup-tables.

Maybe this helps.

Kind regards, mefiX