Fixes #18878: Automatically assign a designated primary MAC address upon creation of a new interface

netbox/dcim/models/device_components.py

@@ -632,10 +632,17 @@ def clean(self):
             })
 
         # Check that the primary MAC address (if any) is assigned to this interface
-        if self.primary_mac_address and self.primary_mac_address.assigned_object != self:
+        if (
+                self.primary_mac_address and
+                self.primary_mac_address.assigned_object is not None and
+                self.primary_mac_address.assigned_object != self
+        ):
             raise ValidationError({
-                'primary_mac_address': _("MAC address {mac_address} is not assigned to this interface.").format(
-                    mac_address=self.primary_mac_address
+                'primary_mac_address': _(
+                    "MAC address {mac_address} is assigned to a different interface ({interface})."
+                ).format(
+                    mac_address=self.primary_mac_address,
+                    interface=self.primary_mac_address.assigned_object,
                 )
             })
 

netbox/dcim/signals.py

@@ -4,6 +4,7 @@
 from django.dispatch import receiver
 
 from dcim.choices import CableEndChoices, LinkStatusChoices
+from virtualization.models import VMInterface
 from .models import (
     Cable, CablePath, CableTermination, ConsolePort, ConsoleServerPort, Device, DeviceBay, FrontPort, Interface,
     InventoryItem, ModuleBay, PathEndpoint, PowerOutlet, PowerPanel, PowerPort, Rack, RearPort, Location,
@@ -170,3 +171,15 @@ def extend_rearport_cable_paths(instance, created, raw, **kwargs):
         rearport = instance.rear_port
         for cablepath in CablePath.objects.filter(_nodes__contains=rearport):
             cablepath.retrace()
+
+
+@receiver(post_save, sender=Interface)
+@receiver(post_save, sender=VMInterface)
+def update_mac_address_interface(instance, created, raw, **kwargs):
+    """
+    When creating a new Interface or VMInterface, check whether a MACAddress has been designated as its primary. If so,
+    assign the MACAddress to the interface.
+    """
+    if created and not raw and instance.primary_mac_address:
+        instance.primary_mac_address.assigned_object = instance
+        instance.primary_mac_address.save()