code: func (subnet HTTPProxyCIDRCheck) Check() (warnings, errorList []error) {
  	klog.V(1).Infoln("validating http connectivity to first IP address in the CIDR")
  	if len(subnet.CIDR) == 0 {
  		return nil, nil
  	}
  
  	_, cidr, err := net.ParseCIDR(subnet.CIDR)
  	if err != nil {
  		return nil, []error{errors.Wrapf(err, "error parsing CIDR %q", subnet.CIDR)}
  	}
  
  	testIP, err := ipallocator.GetIndexedIP(cidr, 1)
  	if err != nil {
  		return nil, []error{errors.Wrapf(err, "unable to get first IP address from the given CIDR (%s)", cidr.String())}
  	}
  
  	testIPstring := testIP.String()
  	if len(testIP) == net.IPv6len {
  		testIPstring = fmt.Sprintf("[%s]:1234", testIP)
  	}
  	url := fmt.Sprintf("%s://%s/", subnet.Proto, testIPstring)
  
  	req, err := http.NewRequest("GET", url, nil)
  	if err != nil {
  		return nil, []error{err}
  	}
  
  	// Utilize same transport defaults as it will be used by API server
  	proxy, err := netutil.SetOldTransportDefaults(&http.Transport{}).Proxy(req)
  	if err != nil {
  		return nil, []error{err}
  	}
  	if proxy != nil {
  		return []error{errors.Errorf("connection to %q uses proxy %q. This may lead to malfunctional cluster setup. Make sure that Pod and Services IP ranges specified correctly as exceptions in proxy configuration", subnet.CIDR, proxy)}, nil
  	}
  	return nil, nil
  }
docs: // Check validates http connectivity to first IP address in the CIDR.
  // If it is not directly connected and goes via proxy it will produce warning.