i have a ubuntu 10.04 with nginx /0.8.54 running as a load balance proxy named: www.local.com

I have two IIS backend servers which responds on Host header request web1.local.com web2.local.com

Problem: When i hit my nginx balancer on www.local.com my backend servers respond with the default server blank webpage (IIS default page) since they are waiting for a right host header (e.g. web1.local.com)

my nginx.conf

upstream backend {
                server web1.local.com:80;
                server web2.local.com:80;
        }
        server {

      listen 80;
            location / {
              proxy_pass  http://backend;
              proxy_set_header        X-Real-IP       $remote_addr;
              proxy_set_header        Host            $proxy_host;
            }
    }

any hint ?