diff --git a/components/neutron/values.yaml b/components/neutron/values.yaml
index 660898ceb..d7967d7f0 100644
--- a/components/neutron/values.yaml
+++ b/components/neutron/values.yaml
@@ -76,7 +76,7 @@ conf:
       # We are also able to see which ones are used from the OpenStack API.
       # - 'segments' enables the /segments API for CRUD operations on network
       # segments.
-      service_plugins: "ovn-router,trunk,network_segment_range,segments,evpn"
+      service_plugins: "ovn-router,trunk,network_segment_range,segments,understack_vni"
       # we don't want HA L3 routers. It's a Python value so we need to quote it in YAML.
       l3_ha: "False"
       # we aren't using availability zones so having calls attempt to add things to
diff --git a/python/neutron-understack/neutron_understack/l3_router/understack_vni_db.py b/python/neutron-understack/neutron_understack/l3_router/understack_vni_db.py
index 329ccd364..e8cad0734 100644
--- a/python/neutron-understack/neutron_understack/l3_router/understack_vni_db.py
+++ b/python/neutron-understack/neutron_understack/l3_router/understack_vni_db.py
@@ -8,7 +8,6 @@
 
 MIN_VNI = getattr(n_const, "MIN_VXLAN_VNI", 1)
 MAX_VNI = n_const.MAX_VXLAN_VNI
-DEFAULT_VNI_RANGES = [f"{MIN_VNI}:{MAX_VNI}"]
 
 
 class UnderstackVNIInvalidRange(n_exc.NeutronException):
diff --git a/python/neutron-understack/neutron_understack/tests/test_understack_vni.py b/python/neutron-understack/neutron_understack/tests/test_understack_vni.py
index e7c773952..fcfd3103d 100644
--- a/python/neutron-understack/neutron_understack/tests/test_understack_vni.py
+++ b/python/neutron-understack/neutron_understack/tests/test_understack_vni.py
@@ -2,6 +2,8 @@
 
 import pytest
 import sqlalchemy as sa
+from neutron_lib.db import api as db_api
+from oslo_db import exception as db_exc
 from sqlalchemy import create_engine
 from sqlalchemy.orm import sessionmaker
 
@@ -94,6 +96,81 @@ def test_auto_allocation_reports_exhaustion(db_context):
         helper.allocate_vni_for_router(db_context, "router-2", 0)
 
 
+def test_router_create_retries_auto_allocation_vni_race(mocker, db_context):
+    helper = understack_vni_db.UnderstackVniDbHelper(vni_ranges=["100:101"])
+    plugin = vrf.UnderstackVniPlugin.__new__(vrf.UnderstackVniPlugin)
+    plugin._vni_db = helper
+    mocker.patch.object(
+        vrf.directory,
+        "get_plugin",
+        return_value=FakeFlavorPlugin(vrf._vrf_provider_driver()),
+    )
+    mocker.patch("oslo_db.api.time.sleep")
+
+    original_flush = db_context.session.flush
+    original_rollback = db_context.session.rollback
+    collided = False
+    winner_inserted = False
+
+    def flush_with_collision(*args, **kwargs):
+        nonlocal collided
+        if not collided:
+            collided = True
+            raise db_exc.DBDuplicateEntry(columns=["vni"], value=100)
+        return original_flush(*args, **kwargs)
+
+    def rollback_and_insert_winner():
+        nonlocal winner_inserted
+        original_rollback()
+        if collided and not winner_inserted:
+            db_context.session.execute(
+                sa.text(
+                    """
+                    INSERT INTO understack_router_vni_allocations
+                        (vni, router_id)
+                    VALUES (:vni, :router_id)
+                    """
+                ),
+                {"vni": 100, "router_id": "router-racer"},
+            )
+            db_context.session.commit()
+            winner_inserted = True
+
+    mocker.patch.object(db_context.session, "flush", side_effect=flush_with_collision)
+    mocker.patch.object(
+        db_context.session, "rollback", side_effect=rollback_and_insert_winner
+    )
+
+    @db_api.retry_if_session_inactive()
+    def create_router(context, plugin):
+        router = {
+            "id": "router-1",
+            "flavor_id": "flavor-1",
+            apidef.EVPN_VNI: 0,
+        }
+        payload = SimpleNamespace(
+            context=context,
+            resource_id="router-1",
+            latest_state=router,
+        )
+
+        plugin._process_router_create(None, None, None, payload)
+        return payload.latest_state[apidef.EVPN_VNI]
+
+    assert create_router(db_context, plugin) == 101
+
+    rows = db_context.session.execute(
+        sa.text(
+            """
+            SELECT vni, router_id
+            FROM understack_router_vni_allocations
+            ORDER BY vni
+            """
+        )
+    ).fetchall()
+    assert rows == [(100, "router-racer"), (101, "router-1")]
+
+
 def test_vrf_router_create_allocates_vni(mocker):
     mocker.patch.object(
         vrf.directory,
diff --git a/python/neutron-understack/uv.lock b/python/neutron-understack/uv.lock
index 556085eef..d59082165 100644
--- a/python/neutron-understack/uv.lock
+++ b/python/neutron-understack/uv.lock
@@ -792,7 +792,7 @@ test = [
 requires-dist = [
     { name = "keystoneauth1", specifier = ">=3.14.0" },
     { name = "neutron", specifier = ">=27,<29" },
-    { name = "neutron-lib", specifier = ">=3,<4" },
+    { name = "neutron-lib", specifier = ">=3,<5" },
     { name = "openstacksdk", specifier = ">=4.9.0" },
     { name = "oslo-config", specifier = ">=9.7.1" },
     { name = "oslo-log", specifier = ">=7.1.0" },