When a site is proxied through Cloudflare, your origin web server access log records a Cloudflare IP address for each incoming request by default. However with the mod_cloudflare tool, you can record the real IP address of incoming requests.
Cloudflare reports the actual visitor IP address in an appended HTTP header called CF-Connecting-IP. However at times when you have other applications that depend on the incoming IP address of the original visitor, certain problems might arise.
To address this issue, you can log real visitor IPs with mod_cloudflare in your origin web server.
The diagram below outlines the different ways that IP addresses are handled with and without Cloudflare. Also, consult these articles for restoring original visitor IPs in specific web servers and CMS platforms.