[ONOS-4606] Avoid generating incorrect NetworkId

Change-Id: I7b474e368cde8e46e3c903326a8052ce555c0c85
diff --git a/incubator/store/src/main/java/org/onosproject/incubator/store/virtual/impl/DistributedVirtualNetworkStore.java b/incubator/store/src/main/java/org/onosproject/incubator/store/virtual/impl/DistributedVirtualNetworkStore.java
index 7ceeb1b..538109d 100644
--- a/incubator/store/src/main/java/org/onosproject/incubator/store/virtual/impl/DistributedVirtualNetworkStore.java
+++ b/incubator/store/src/main/java/org/onosproject/incubator/store/virtual/impl/DistributedVirtualNetworkStore.java
@@ -256,9 +256,13 @@
      * @return NetworkId network identifier
      */
     private NetworkId genNetworkId() {
-        return NetworkId.networkId(idGenerator.getNewId());
-    }
+        NetworkId networkId;
+        do {
+            networkId = NetworkId.networkId(idGenerator.getNewId());
+        } while (!networkId.isVirtualNetworkId());
 
+        return networkId;
+    }
 
     @Override
     public void removeNetwork(NetworkId networkId) {