Dockerd won't start if a network with the default subnet prefix already exists in HNS.

Signed-off-by: Pradip Dhara <pradipd@microsoft.com>

daemon/daemon_windows.go

@@ -33,7 +33,6 @@ import (
 
 const (
 	isWindows            = true
-	defaultNetworkSpace  = "172.16.0.0/12"
 	platformSupported    = true
 	windowsMinCPUShares  = 1
 	windowsMaxCPUShares  = 10000
@@ -424,15 +423,19 @@ func initBridgeDriver(controller libnetwork.NetworkController, config *config.Co
 		winlibnetwork.NetworkName: runconfig.DefaultDaemonNetworkMode().NetworkName(),
 	}
 
-	subnetPrefix := defaultNetworkSpace
+	var ipamOption libnetwork.NetworkOption
+	var subnetPrefix string
+
 	if config.BridgeConfig.FixedCIDR != "" {
 		subnetPrefix = config.BridgeConfig.FixedCIDR
 	}
 
-	ipamV4Conf := libnetwork.IpamConf{PreferredPool: subnetPrefix}
-	v4Conf := []*libnetwork.IpamConf{&ipamV4Conf}
-	v6Conf := []*libnetwork.IpamConf{}
-	ipamOption := libnetwork.NetworkOptionIpam("default", "", v4Conf, v6Conf, nil)
+	if subnetPrefix != "" {
+		ipamV4Conf := libnetwork.IpamConf{PreferredPool: subnetPrefix}
+		v4Conf := []*libnetwork.IpamConf{&ipamV4Conf}
+		v6Conf := []*libnetwork.IpamConf{}
+		ipamOption = libnetwork.NetworkOptionIpam("default", "", v4Conf, v6Conf, nil)
+	}
 
 	_, err := controller.NewNetwork(string(runconfig.DefaultDaemonNetworkMode()), runconfig.DefaultDaemonNetworkMode().NetworkName(), "",
 		libnetwork.NetworkOptionGeneric(options.Generic{