Unable to use custom variable with limit_conn_zone (1 reply)

I am trying to use the limit connections / limit request. I have the server behind a proxy, the proxy has the following line :

proxy_set_header X-Real-IP $remote_addr;

and in my nginx.conf on my server behind the proxy i have :

limit_conn_zone $http_x_real_ip zone=perip:10m;
limit_conn perip 20;
limit_req_zone $http_x_real_ip zone=forward:10m rate=60r/m;

However, when checking my logs, I get the internal address of the proxy server listed, not the external real ip :

2014/09/27 13:45:16 [error] 57287#0: *29475 limiting requests, excess: 30.536 by zone "forward", client: 10.120.23.133

Can you see an issue with my configuration, or is there a bug with nginx in respect to using custom variables?