Difference between "True client ip" and "X-Forwarded for"

Hello,

Actually the XFF header is inserted exactly for that purpose... to let the backend server knows the "real client IP addr".

Indead, when you have a reverse proxy between your client and server. The reverse proxy most of the time (for simplicity) change the source client IP (this is what we call SNAT is F5 references). So in order to let the server know who is behind the reverse proxy, the F5 can insert the XFF header with the client addr.

In that manner, once the request is forwarded to the client it can process this info.

Hope it clarifies.

Regards

For more info check the following link

https://support.f5.com/csp/article/K4816

Hi,

Before 2014, there was no standard http header to insert proxies client ip.

The most common non standard http header was X-Forwarded-For.

Some other proxy / reverse proxy use true-cient-ip (like Akamai)

RFC 7239 describe new standard but is not well deployed yet.