diff --git a/core/api/src/main/java/org/onosproject/net/flow/Extension.java b/core/api/src/main/java/org/onosproject/net/flow/Extension.java
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+++ b/core/api/src/main/java/org/onosproject/net/flow/Extension.java
@@ -0,0 +1,71 @@
+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.net.flow;
+
+import org.onosproject.net.flow.instructions.ExtensionPropertyException;
+
+import java.util.List;
+
+/**
+ * An extension to the northbound APIs.
+ */
+public interface Extension {
+
+    /**
+     * Sets a property on the extension.
+     *
+     * @param key property key
+     * @param value value to set for the given key
+     * @param <T> class of the value
+     * @throws ExtensionPropertyException if the given key is not a valid
+     * property on this extension
+     */
+    <T> void setPropertyValue(String key, T value) throws ExtensionPropertyException;
+
+    /**
+     * Gets a property value of an extension.
+     *
+     * @param key property key
+     * @param <T> class of the value
+     * @return value of the property
+     * @throws ExtensionPropertyException if the given key is not a valid
+     * property on this extension
+     */
+    <T> T getPropertyValue(String key) throws ExtensionPropertyException;
+
+    /**
+     * Gets a list of all properties on the extension.
+     *
+     * @return list of properties
+     */
+    List<String> getProperties();
+
+    /**
+     * Serialize the extension to a byte array.
+     *
+     * @return byte array
+     */
+    byte[] serialize();
+
+    /**
+     * Deserialize the extension from a byte array. The properties
+     * of this object will be overwritten with the data in the byte array.
+     *
+     * @param data input byte array
+     */
+    void deserialize(byte[] data);
+}