Introduction

Cloudflare uses X-Forwarded-For header. The header is used to store the original IP address when the request is forwarded using a proxy.

You will need the Module ngx_http_realip_module.

First step: Verify that you have the ngx_http_realip_module

Check the output of the next command and search for the string ngx_realip or --with-http_realip_module

nginx -V

Second step: Recompile with realip module (optional)

If your nginx was missing the realip module you will need to recompile it: Skip this step if you have the realip module.

wget http://nginx.org/download/nginx-1.7.4.tar.gz
tar -zxvf nginx-1.7.4.tar.gz
./configure --with-http_realip_module # Add all other options
make
sudo make install

When you executed nginx -V it will output other modules, add those options to the ./configure.

Third step: Configuration

Open the file /etc/nginx/nginx.conf add the following in the http block, or in the server block:

set_real_ip_from 103.21.244.0/22;
set_real_ip_from 103.22.200.0/22;
set_real_ip_from 103.31.4.0/22;
set_real_ip_from 104.16.0.0/12;
set_real_ip_from 108.162.192.0/18;
set_real_ip_from 131.0.72.0/22;
set_real_ip_from 141.101.64.0/18;
set_real_ip_from 162.158.0.0/15;
set_real_ip_from 172.64.0.0/13;
set_real_ip_from 173.245.48.0/20;
set_real_ip_from 188.114.96.0/20;
set_real_ip_from 190.93.240.0/20;
set_real_ip_from 197.234.240.0/22;
set_real_ip_from 198.41.128.0/17;
set_real_ip_from 2400:cb00::/32;
set_real_ip_from 2606:4700::/32;
set_real_ip_from 2803:f800::/32;
set_real_ip_from 2405:b500::/32;
set_real_ip_from 2405:8100::/32;
set_real_ip_from 2c0f:f248::/32;
set_real_ip_from 2a06:98c0::/29;

# use any of the following two
real_ip_header CF-Connecting-IP;
#real_ip_header X-Forwarded-For;