diff --git src/wp-includes/class-wp-network.php src/wp-includes/class-wp-network.php
old mode 100644
new mode 100755
index 5ab29c2..a776ed4
--- src/wp-includes/class-wp-network.php
+++ src/wp-includes/class-wp-network.php
@@ -17,9 +17,6 @@
  * ability to interact with any network of sites is required.
  *
  * @since 4.4.0
- *
- * @property int $id
- * @property int $site_id
  */
 class WP_Network {
 
@@ -30,10 +27,11 @@
 	 * @since 4.6.0 Converted from public to private to explicitly enable more intuitive
 	 *              access via magic methods. As part of the access change, the type was
 	 *              also changed from `string` to `int`.
-	 * @access private
+	 * @since 4.7.0 Converted back to public
+	 * @access public
 	 * @var int
 	 */
-	private $id;
+	public $id;
 
 	/**
 	 * Domain of the network.
@@ -56,16 +54,13 @@
 	/**
 	 * The ID of the network's main site.
 	 *
-	 * Named "blog" vs. "site" for legacy reasons. A main site is mapped to
-	 * the network when the network is created.
+	 * Every network has a "main site" mapped to it when it is created.
 	 *
-	 * A numeric string, for compatibility reasons.
-	 *
-	 * @since 4.4.0
-	 * @access private
-	 * @var string
+	 * @since 4.7.0
+	 * @access public
+	 * @var int
 	 */
-	private $blog_id = '0';
+	public $site_id = 0;
 
 	/**
 	 * Domain used to set cookies for this network.
@@ -98,7 +93,7 @@
 	 * @param int $network_id The ID of the network to retrieve.
 	 * @return WP_Network|bool The network's object if found. False if not.
 	 */
-	public static function get_instance( $network_id ) {
+	public static function get_instance( $network_id = 0 ) {
 		global $wpdb;
 
 		$network_id = (int) $network_id;
@@ -134,7 +129,7 @@
 	 */
 	public function __construct( $network ) {
 		foreach( get_object_vars( $network ) as $key => $value ) {
-			$this->$key = $value;
+			$this->__set( $key, $value );
 		}
 
 		$this->_set_site_name();
@@ -156,10 +151,12 @@
 		switch ( $key ) {
 			case 'id';
 				return (int) $this->id;
-			case 'blog_id':
-				return $this->blog_id;
 			case 'site_id':
-				return (int) $this->blog_id;
+				return (int) $this->site_id;
+
+			// Support blog_id for legacy reasons
+			case 'blog_id':
+				return (string) $this->site_id;
 		}
 
 		return null;
@@ -179,8 +176,10 @@
 	public function __isset( $key ) {
 		switch ( $key ) {
 			case 'id':
-			case 'blog_id':
 			case 'site_id':
+
+			// Support blog_id for legacy reasons
+			case 'blog_id':
 				return true;
 		}
 
@@ -203,9 +202,11 @@
 			case 'id':
 				$this->id = (int) $value;
 				break;
+
+			// Support blog_id for legacy reasons
 			case 'blog_id':
 			case 'site_id':
-				$this->blog_id = (string) $value;
+				$this->site_id = (int) $value;
 				break;
 			default:
 				$this->$key = $value;