diff --git a/api-ref/source/v2/intro.inc b/api-ref/source/v2/intro.inc
index 518eb0b08..9c063c7fb 100644
--- a/api-ref/source/v2/intro.inc
+++ b/api-ref/source/v2/intro.inc
@@ -145,6 +145,16 @@ admin_state_up=True and shared=True and named ``foobar`` or ``bizbaz``:
 
     GET /v2.0/networks?name=foobar&name=bizbaz&admin_state_up=True&shared=True
 
+Starting from Rocky release, the Networking API might support filtering
+attributes with empty value. For example, the request below lists all ports
+that have ``device_id`` attribute with empty value (which are unbound ports).
+
+.. code::
+
+    GET /v2.0/networks?device_id=
+
+To determine if this feature is supported, a user can check whether the
+``empty-string-filtering`` extension API is available.
 
 Note
 ----
diff --git a/neutron_lib/api/definitions/__init__.py b/neutron_lib/api/definitions/__init__.py
index af5e23243..a903af5e2 100644
--- a/neutron_lib/api/definitions/__init__.py
+++ b/neutron_lib/api/definitions/__init__.py
@@ -24,6 +24,7 @@ from neutron_lib.api.definitions import dhcpagentscheduler
 from neutron_lib.api.definitions import dns
 from neutron_lib.api.definitions import dns_domain_ports
 from neutron_lib.api.definitions import dvr
+from neutron_lib.api.definitions import empty_string_filtering
 from neutron_lib.api.definitions import external_net
 from neutron_lib.api.definitions import extra_dhcp_opt
 from neutron_lib.api.definitions import extraroute
@@ -96,6 +97,7 @@ _ALL_API_DEFINITIONS = {
     dns,
     dns_domain_ports,
     dvr,
+    empty_string_filtering,
     external_net,
     extra_dhcp_opt,
     extraroute,
diff --git a/neutron_lib/api/definitions/base.py b/neutron_lib/api/definitions/base.py
index f0cb08b3e..a955efc09 100644
--- a/neutron_lib/api/definitions/base.py
+++ b/neutron_lib/api/definitions/base.py
@@ -86,6 +86,7 @@ KNOWN_EXTENSIONS = (
     'dns-domain-ports',
     'dns-integration',
     'dvr',
+    'empty-string-filtering',
     'ext-gw-mode',
     'external-net',
     'extra_dhcp_opt',
diff --git a/neutron_lib/api/definitions/empty_string_filtering.py b/neutron_lib/api/definitions/empty_string_filtering.py
new file mode 100644
index 000000000..345a16883
--- /dev/null
+++ b/neutron_lib/api/definitions/empty_string_filtering.py
@@ -0,0 +1,25 @@
+#    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.
+
+
+ALIAS = 'empty-string-filtering'
+IS_SHIM_EXTENSION = True
+IS_STANDARD_ATTR_EXTENSION = False
+NAME = 'Empty String Filtering Extension'
+DESCRIPTION = 'Allow filtering by attributes with empty string value'
+UPDATED_TIMESTAMP = '2018-05-01T10:00:00-00:00'
+RESOURCE_ATTRIBUTE_MAP = {}
+SUB_RESOURCE_ATTRIBUTE_MAP = {}
+ACTION_MAP = {}
+REQUIRED_EXTENSIONS = []
+OPTIONAL_EXTENSIONS = []
+ACTION_STATUS = {}
diff --git a/neutron_lib/tests/unit/api/definitions/test_empty_string_filtering.py b/neutron_lib/tests/unit/api/definitions/test_empty_string_filtering.py
new file mode 100644
index 000000000..f4188ec4e
--- /dev/null
+++ b/neutron_lib/tests/unit/api/definitions/test_empty_string_filtering.py
@@ -0,0 +1,18 @@
+#    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.
+
+from neutron_lib.api.definitions import empty_string_filtering
+from neutron_lib.tests.unit.api.definitions import base
+
+
+class EmptyStringFilteringDefinitionTestCase(base.DefinitionBaseTestCase):
+    extension_module = empty_string_filtering
diff --git a/releasenotes/notes/add-empty-string-filtering-api-extension-44cb392025dc359c.yaml b/releasenotes/notes/add-empty-string-filtering-api-extension-44cb392025dc359c.yaml
new file mode 100644
index 000000000..c19b89d06
--- /dev/null
+++ b/releasenotes/notes/add-empty-string-filtering-api-extension-44cb392025dc359c.yaml
@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    Add ``empty-string-filtering`` API extension. This extension indicates
+    if the server supports filtering attributes with empty value.