From 05fd14a59af4adc96b75c8096a43fad146c67eb9 Mon Sep 17 00:00:00 2001
From: Martin Hauser <git@pheus.dev>
Date: Tue, 28 Oct 2025 14:11:46 +0100
Subject: [PATCH] fix(ipam): Correct VLAN ID range calculation logic
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Adjust VLAN ID range calculation to use half‑open intervals for
consistency. Add a test to validate `_total_vlan_ids`.

Fixes #20610
---
 .../0083_vlangroup_populate_total_vlan_ids.py | 27 +++++++++++++++++++
 netbox/ipam/models/vlans.py                   |  3 ++-
 netbox/ipam/tests/test_models.py              |  4 +++
 3 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 netbox/ipam/migrations/0083_vlangroup_populate_total_vlan_ids.py

diff --git a/netbox/ipam/migrations/0083_vlangroup_populate_total_vlan_ids.py b/netbox/ipam/migrations/0083_vlangroup_populate_total_vlan_ids.py
new file mode 100644
index 00000000000..4308975881f
--- /dev/null
+++ b/netbox/ipam/migrations/0083_vlangroup_populate_total_vlan_ids.py
@@ -0,0 +1,27 @@
+from django.db import migrations
+
+
+def populate_vlangroup_total_vlan_ids(apps, schema_editor):
+    VLANGroup = apps.get_model('ipam', 'VLANGroup')
+    db_alias = schema_editor.connection.alias
+
+    vlan_groups = VLANGroup.objects.using(db_alias).only('id', 'vid_ranges')
+    for group in vlan_groups:
+        total_vlan_ids = 0
+        if group.vid_ranges:
+            for r in group.vid_ranges:
+                # Half-open [lo, hi): length is (hi - lo).
+                if r is not None and r.lower is not None and r.upper is not None:
+                    total_vlan_ids += r.upper - r.lower
+        group._total_vlan_ids = total_vlan_ids
+    VLANGroup.objects.using(db_alias).bulk_update(vlan_groups, ['_total_vlan_ids'], batch_size=100)
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ('ipam', '0082_add_prefix_network_containment_indexes'),
+    ]
+
+    operations = [
+        migrations.RunPython(populate_vlangroup_total_vlan_ids, migrations.RunPython.noop),
+    ]
diff --git a/netbox/ipam/models/vlans.py b/netbox/ipam/models/vlans.py
index efa1ed39ed3..030633330a4 100644
--- a/netbox/ipam/models/vlans.py
+++ b/netbox/ipam/models/vlans.py
@@ -132,7 +132,8 @@ def clean(self):
     def save(self, *args, **kwargs):
         self._total_vlan_ids = 0
         for vid_range in self.vid_ranges:
-            self._total_vlan_ids += vid_range.upper - vid_range.lower + 1
+            # VID range is inclusive on lower-bound, exclusive on upper-bound
+            self._total_vlan_ids += vid_range.upper - vid_range.lower
 
         super().save(*args, **kwargs)
 
diff --git a/netbox/ipam/tests/test_models.py b/netbox/ipam/tests/test_models.py
index 656f62d87c2..c93a47d21fe 100644
--- a/netbox/ipam/tests/test_models.py
+++ b/netbox/ipam/tests/test_models.py
@@ -661,6 +661,10 @@ def test_overlapping_vlan(self):
         vlangroup.full_clean()
         vlangroup.save()
 
+    def test_total_vlan_ids(self):
+        vlangroup = VLANGroup.objects.first()
+        self.assertEqual(vlangroup._total_vlan_ids, 100)
+
 
 class TestVLAN(TestCase):