nginx 配置 upstream backup 报错 ,求 V 友解答

nginx是window版本
version: nginx-1.11.9

http {

    upstream backend {
    ip_hash;

    server 127.0.0.1:8080 max_fails=3 fail_timeout=20s;  

    server 127.0.0.1:8086 backup;  
    }  
   
    server {
        listen       83;
        server_name 127.0.0.1;
        location / {  
            proxy_pass http://backend;  
        }  
    }

}

启动 nginx 的时候 报错 错误信息如下:

2017/02/06 10:55:21 [emerg] 7568#4548: 
balancing method does not support parameter "backup" in C:\nginx-1.11.9/conf/nginx.conf:51