diff --git a/kubetest2-gke/deployer/deployer.go b/kubetest2-gke/deployer/deployer.go
index d93dc4a..c5a04ef 100644
--- a/kubetest2-gke/deployer/deployer.go
+++ b/kubetest2-gke/deployer/deployer.go
@@ -201,6 +201,7 @@ func NewDeployer(opts types.Options) *Deployer {
 		},
 		NetworkOptions: &options.NetworkOptions{
 			Network:               "default",
+			UseCustomSubnetMode:   false,
 			RemoveNetwork:         true,
 			EnableULAInternalIPv6: false,
 		},
diff --git a/kubetest2-gke/deployer/network.go b/kubetest2-gke/deployer/network.go
index d775380..7b4e5cc 100644
--- a/kubetest2-gke/deployer/network.go
+++ b/kubetest2-gke/deployer/network.go
@@ -73,6 +73,10 @@ func (d *Deployer) VerifyNetworkFlags() error {
 		if err := validateSubnetRanges(d.SubnetworkRanges); err != nil {
 			return err
 		}
+
+		if !d.UseCustomSubnetMode {
+			return errors.New("the 'auto' subnet mode cannot be used for multi-project profile")
+		}
 	}
 
 	return d.internalizeNetworkFlags(numProjects)
@@ -148,18 +152,18 @@ func (d *Deployer) internalizeNetworkFlags(numProjects int) error {
 
 func (d *Deployer) CreateNetwork() error {
 	// Create network if it doesn't exist.
-	// For single project profile, the subnet-mode could be auto for simplicity.
-	// For multiple projects profile, the subnet-mode must be custom and should only be created in the host project.
-	//   (Here we consider the first project to be the host project and the rest be service projects)
-	//   Reference: https://cloud.google.com/kubernetes-engine/docs/how-to/cluster-shared-vpc#creating_a_network_and_two_subnets
-	subnetMode := "auto"
-	if len(d.Projects) > 1 {
-		subnetMode = "custom"
-	}
 	if runWithNoOutput(exec.Command("gcloud", "compute", "networks", "describe", d.Network,
 		"--project="+d.Projects[0],
 		"--format=value(name)")) != nil {
 		// Assume error implies non-existent.
+		// For single project profile, the subnet-mode could be auto for simplicity.
+		// For multiple projects profile, the subnet-mode must be custom and should only be created in the host project.
+		//   (Here we consider the first project to be the host project and the rest be service projects)
+		//   Reference: https://cloud.google.com/kubernetes-engine/docs/how-to/cluster-shared-vpc#creating_a_network_and_two_subnets
+		subnetMode := "auto"
+		if d.UseCustomSubnetMode || len(d.Projects) > 1 {
+			subnetMode = string("custom")
+		}
 		// TODO(chizhg): find a more reliable way to check if the network exists or not.
 		klog.V(1).Infof("Couldn't describe network %q, assuming it doesn't exist and creating it", d.Network)
 		createNetworkCommand := []string{
diff --git a/kubetest2-gke/deployer/options/network.go b/kubetest2-gke/deployer/options/network.go
index e6ca5d8..e8dc7ea 100644
--- a/kubetest2-gke/deployer/options/network.go
+++ b/kubetest2-gke/deployer/options/network.go
@@ -23,6 +23,7 @@ type NetworkOptions struct {
 	PrivateClusterMasterIPRanges []string `flag:"~private-cluster-master-ip-range" desc:"Private cluster master IP ranges. It should be IPv4 CIDR(s), and its length must be the same as the number of clusters if private cluster is requested."`
 	SubnetworkRanges             []string `flag:"~subnetwork-ranges" desc:"Subnetwork ranges as required for shared VPC setup as described in https://cloud.google.com/kubernetes-engine/docs/how-to/cluster-shared-vpc#creating_a_network_and_two_subnets. For multi-project profile, it is required and should be in the format of 10.0.4.0/22 10.0.32.0/20 10.4.0.0/14,172.16.4.0/22 172.16.16.0/20 172.16.4.0/22, where the subnetworks configuration for different project are separated by comma, and the ranges of each subnetwork configuration is separated by space."`
 	EnableULAInternalIPv6        bool     `flag:"~enable-ula-internal-ipv6" desc:"Enable Unique Local IPv6 Addresses (ULA). Adds the --enable-ula-internal-ipv6 flag to the gcloud compute networks create command"`
+	UseCustomSubnetMode          bool     `flag:"~use-custom-subnet-mode" desc:"Use '--subnet-mode=custom' when creating the network. Effective only for single-project deployments, as multi-project deployments always use 'custom' mode. Defaults to false."`
 
 	RemoveNetwork bool `flag:"~remove-network" desc:"At the end of the test remove non-default network that was used by cluster. The 'default' network is never deleted. Defaults to true if not provided."`
 }