diff --git a/crd/overlayextensionconfig/api/v1alpha1/overlayextensionconfig_types.go b/crd/overlayextensionconfig/api/v1alpha1/overlayextensionconfig_types.go
index 9d5d220d59..38afcfc6bf 100644
--- a/crd/overlayextensionconfig/api/v1alpha1/overlayextensionconfig_types.go
+++ b/crd/overlayextensionconfig/api/v1alpha1/overlayextensionconfig_types.go
@@ -34,11 +34,14 @@ type OverlayExtensionConfigList struct {
 // +kubebuilder:validation:XValidation:rule="!has(oldSelf.extensionIPRange) || has(self.extensionIPRange)", message="ExtensionIPRange is required once set"
 type OverlayExtensionConfigSpec struct {
 	// ExtensionIPRange field defines a CIDR that should be able to reach routing domain ip addresses.
-	// +kubebuilder:validation:Optional
 	// +kubebuilder:validation:XValidation:rule="self == oldSelf",message="Value is immutable"
 	// +kubebuilder:validation:MaxLength=43
 	// 43 is max length of IPv6 CIDR string
 	ExtensionIPRange string `json:"extensionIPRange,omitempty"`
+
+	// AppGatewaySubnetID field defines a subnet delegated to Application Gateway that should be able to reach routing domain ip addresses.
+	// +kubebuilder:validation:XValidation:rule="self == oldSelf",message="Value is immutable"
+	AppGatewaySubnetID string `json:"appGatewaySubnetID,omitempty"`
 }
 
 type OECState string
diff --git a/crd/overlayextensionconfig/manifests/acn.azure.com_overlayextensionconfigs.yaml b/crd/overlayextensionconfig/manifests/acn.azure.com_overlayextensionconfigs.yaml
index 418691c2af..a5e24be101 100644
--- a/crd/overlayextensionconfig/manifests/acn.azure.com_overlayextensionconfigs.yaml
+++ b/crd/overlayextensionconfig/manifests/acn.azure.com_overlayextensionconfigs.yaml
@@ -47,6 +47,14 @@ spec:
           spec:
             description: OverlayExtensionConfigSpec defines the desired state of OverlayExtensionConfig.
             properties:
+              appGatewaySubnetID:
+                description: AppGatewaySubnetID field defines a subnet delegated to
+                  Application Gateway that should be able to reach routing domain
+                  ip addresses.
+                type: string
+                x-kubernetes-validations:
+                - message: Value is immutable
+                  rule: self == oldSelf
               extensionIPRange:
                 description: |-
                   ExtensionIPRange field defines a CIDR that should be able to reach routing domain ip addresses.