diff --git a/neutron_lib/agent/__init__.py b/neutron_lib/agent/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/neutron_lib/agent/constants.py b/neutron_lib/agent/constants.py
new file mode 100644
index 000000000..eefc3e61a
--- /dev/null
+++ b/neutron_lib/agent/constants.py
@@ -0,0 +1,23 @@
+#    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.
+
+###################################
+# Agent extension related constants
+###################################
+# Extension driver type for Open vSwitch mech driver
+OVS_EXTENSION_DRIVER = 'ovs'
+# Extension driver type for Linux Bridge mech driver
+LB_EXTENSION_DRIVER = 'linuxbridge'
+# Extension driver type for macvtap mech driver
+MACVTAP_EXTENSION_DRIVER = 'macvtap'
+# Extension driver type for SR-IOV mech driver
+SRIOV_EXTENSION_DRIVER = 'sriov'
diff --git a/neutron_lib/agent/extension.py b/neutron_lib/agent/extension.py
new file mode 100644
index 000000000..d814cc8f8
--- /dev/null
+++ b/neutron_lib/agent/extension.py
@@ -0,0 +1,48 @@
+#    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.
+
+import abc
+
+import six
+
+
+@six.add_metaclass(abc.ABCMeta)
+class AgentExtension(object):
+    """Define stable abstract interface for agent extensions.
+
+    An agent extension extends the agent core functionality.
+    """
+
+    @abc.abstractmethod
+    def initialize(self, connection, driver_type):
+        """Perform agent core resource extension initialization.
+
+        :param connection: RPC connection that can be reused by the extension
+                           to define its RPC endpoints
+        :param driver_type: String that defines the agent type to the
+                            extension. Can be used to choose the right backend
+                            implementation.
+
+        Called after all extensions have been loaded.
+        No resource (port, policy, router, etc.) handling will be called before
+        this method.
+        """
+
+    def consume_api(self, agent_api):
+        """Consume the AgentAPI instance from the AgentExtensionsManager.
+
+        Allows an extension to gain access to resources internal to the
+        neutron agent and otherwise unavailable to the extension.  Examples of
+        such resources include bridges, ports, and routers.
+
+        :param agent_api: An instance of an agent-specific API.
+        """
diff --git a/neutron_lib/agent/l2_extension.py b/neutron_lib/agent/l2_extension.py
new file mode 100644
index 000000000..6d7daad0e
--- /dev/null
+++ b/neutron_lib/agent/l2_extension.py
@@ -0,0 +1,55 @@
+#    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.
+
+import abc
+
+import six
+
+from neutron_lib.agent import extension
+
+
+@six.add_metaclass(abc.ABCMeta)
+class L2AgentExtension(extension.AgentExtension):
+    """Define stable abstract interface for l2 agent extensions.
+
+    An agent extension extends the agent core functionality.
+    """
+
+    def initialize(self, connection, driver_type):
+        """Initialize agent extension.
+
+        :param connection: RPC connection that can be reused by the extension
+                           to define its RPC endpoints
+        :param driver_type: String that defines the agent type to the
+                            extension. Can be used to choose the right backend
+                            implementation.
+        """
+
+    @abc.abstractmethod
+    def handle_port(self, context, data):
+        """Handle a port add/update event.
+
+        This can be called on either create or update, depending on the
+        code flow. Thus, it's this function's responsibility to check what
+        actually changed.
+
+        :param context: RPC context.
+        :param data: Port data.
+        """
+
+    @abc.abstractmethod
+    def delete_port(self, context, data):
+        """Handle a port delete event.
+
+        :param context: RPC context.
+        :param data: Port data.
+        """
diff --git a/neutron_lib/agent/l3_extension.py b/neutron_lib/agent/l3_extension.py
new file mode 100644
index 000000000..c7876770c
--- /dev/null
+++ b/neutron_lib/agent/l3_extension.py
@@ -0,0 +1,53 @@
+#    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.
+
+import abc
+
+import six
+
+from neutron_lib.agent import extension
+
+
+@six.add_metaclass(abc.ABCMeta)
+class L3AgentExtension(extension.AgentExtension):
+    """Define stable abstract interface for l3 agent extensions.
+
+    An agent extension extends the agent core functionality.
+    """
+
+    @abc.abstractmethod
+    def add_router(self, context, data):
+        """Handle a router add event.
+
+        Called on router create.
+
+        :param context: RPC context.
+        :param data: Router data.
+        """
+
+    @abc.abstractmethod
+    def update_router(self, context, data):
+        """Handle a router update event.
+
+        Called on router update.
+
+        :param context: RPC context.
+        :param data: Router data.
+        """
+
+    @abc.abstractmethod
+    def delete_router(self, context, data):
+        """Handle a router delete event.
+
+        :param context: RPC context.
+        :param data: Router data.
+        """
diff --git a/releasenotes/notes/agent_extensions-2b497ff33c6dc3e8.yaml b/releasenotes/notes/agent_extensions-2b497ff33c6dc3e8.yaml
new file mode 100644
index 000000000..6180d6fd5
--- /dev/null
+++ b/releasenotes/notes/agent_extensions-2b497ff33c6dc3e8.yaml
@@ -0,0 +1,3 @@
+---
+features:
+  - Neutron agent extension abstract classes are moved from ``neutron.agent`` to ``neutron_lib.agent``