HTTP headers contain more information about you, like your IP, and the used proxy. Depending on the proxy type, some of those variables are present or not.
| Proxy type | HTTP header | Client can | Proxy can | ||
| REMOTE_ADDR(1) | HTTP_VIA | HTTP_X_FORWARDED_FOR | be found | be detected | |
| No proxy | Client IP | (not set) | not set or client IP | Yes | - |
| Transparent proxy | Proxy IP | Proxy IP | Client IP, optionnally followed by proxy IP | Yes | Yes |
| Anonymous proxy | Proxy IP | Proxy IP | Proxy IP | No | Yes |
| Anonymous proxy (distorting) | Proxy IP | Proxy IP | Random IP | Yes | No |
| Elite proxy | Proxy IP | (not set) | not set or client IP | Yes | Yes(2) |
(1) HTTP_X_REMOTE_ADDR is used primarily, then REMOTE_ADDR if first isn't provided
(2) there is still one way to detect that the caller is a proxy by using an identified proxy servers list and match the calling IP.
Basically, transparent proxy servers won't preserve any anonymity, whereas anonymous and elite proxy servers will (elite proxy server being also undetectable)
See explanation on different proxy types at http://www.freeproxy.ru/en/free_proxy/faq/proxy_anonymity.htm
Your proxy type is Unable to check, missing header
| REMOTE_ADDR | 38.107.191.91 |
| HTTP-Via | |
| HTTP-X-Forwarded-For | 38.107.191.91 |
| HTTP-X-Proxy-Type | Error |
| HTTP-X-Transparent | |
| HTTP-X-Proxy-Detectable | |
| HTTP-X-Original-IP | 38.107.191.91 |
| HTTP-X-Transparent | HTTP-X-Proxy-Detectable | Resulting proxy type |
| true | false | None |
| true | true | Transparent |
| false | true | Anonymous / Distorting |
| false | false | Elite (high anonymity) |
| Error, you didn't provide HTTP-X-Original-IP header |