Cable Bulk Uploads allow mark_connected AND a cable to be present (validation error)

[cruse1977]

NetBox Edition

NetBox Community

NetBox Version

v4.4.4

Python Version

3.10

Steps to Reproduce

1. Create a device (eg: dmi-albany-rtr01) with interfaces GigabitEthernet0/1/6 and GigabitEthernet0/1/7 in a site "DM-Albany"

2. On dmi01-albany-rtr01, set interface GigabitEthernet0/1/6 as mark connected and save.

3. Bulk Upload the following

side_a_device, side_a_type, side_a_name, side_b_device, side_b_type, side_b_name, side_a_site, side_b_site
"dmi01-albany-rtr01", "dcim.interface", "GigabitEthernet0/1/6", "dmi01-albany-rtr01", "dcim.interface", "GigabitEthernet0/1/7", "DM-Albany", "DM-Albany"

Expected Behavior

Upload fails due to mark_connected being set, and adding a cable to that interface

Observed Behavior

Cable is allowed, however this will manifest in netbox-branching as a branch failing to sync or merge, due to the validation error of mark_connected AND cable - Screenshot showing the update change entry which will cause this:

[pheus]

I'd like to contribute this bugfix. Could you please assign the issue to me? Thanks!

[pheus]

Just to add a UI angle: this can also happen in the web UI due to a stale selection. The interface dropdowns correctly disable endpoints that are already cabled or have mark_connected=True. However:

1. Open the cable form and select an eligible interface.
2. Before submitting, the interface is edited (by you in another tab or by someone else) to change its state — e.g., set mark_connected=True.
3. Submitting the form may still proceed because the selection was made against the earlier state.

The “already cabled” case is typically caught by the existing duplicate‑termination check, but the mark_connected case isn’t enforced at the model layer today. The PR addresses this by adding a guard in CableTermination.clean() so a cable cannot be attached when the endpoint has mark_connected=True. That closes the UI/API/CSV gap and returns a clear validation error instead of allowing an inconsistent state.