ip masking in nginx

gistfile1.txt

map $remote_addr $remote_addr_anon {
    ~(?P<ip>\d+\.\d+)\.         $ip.0.0;
    ~(?P<ip>[^:]+:[^:]+):       $ip::;
    default                     0.0.0.0;
}
map $http_x_forwarded_for $http_x_forwarded_for_anon {
    ~(?P<ip>\d+\.\d+)\.         $ip.0.0;
    ~(?P<ip>[^:]+:[^:]+):       $ip::;
    default                     0.0.0.0;                                                    
}

log_format  main  '$remote_addr_anon - $remote_user [$time_local] "$request" ' 
                  '$status $body_bytes_sent "$http_referer" '
                  '"$http_user_agent" "$http_x_forwarded_for_anon"';