Q: Can you disable Automatic Broadcast Domain creation?
Automatic Broadcast Domain creation - actually - Auto Port Placement - was introduced in ONTAP 9.8. Whilst I never had any problem creating Broadcast Domains manually, I understand why the feature was introduced, and it is a cool feature if you can learn to work with it (which is something I've not got used to yet, I just broadcast-domain delete the auto generated stuff - I'm a bit of dinosaur! 🙂)
ONTAP 9.8: Auto Port Placement
ONTAP can automatically configure broadcast domains, select ports, and help configure network interfaces (LIFs), virtual LANs (VLANs), and link aggregation groups (LAGs) based on reachability and network topology detection.
When you first create a cluster, ONTAP automatically discovers the networks connected to ports and configures the needed broadcast domains based on layer 2 reachability. You no longer have to configure broadcast domains manually.
... depending on your network topology, ONTAP configures additional broadcast domains as needed: Default-1, Default-2, and so on. You can rename these broadcast domains if desired, but do not modify which ports are configured in these broadcast domains.
When you configure network interfaces, the home port selection is optional. If you do not manually select a home port, ONTAP will attempt to assign an appropriate home port in the same broadcast domain as other network interfaces in the same subnet.
When creating a VLAN or adding the first port to a newly created LAG, ONTAP will attempt to automatically assign the VLAN or LAG to the appropriate broadcast domain based on its layer 2 reachability.
By automatically configuring broadcast domains and ports, ONTAP helps to ensure that clients maintain access to their data during failover to another port or node in the cluster.
Skip Broadcast Domain Placement
If you are creating VLAN ports, there is this flag for:
network port vlan create
[-skip-broadcast-domain-placement [true]] - Skip Placement Into Broadcast Domain (privilege: advanced) When specified, the VLAN will not be placed into any broadcast domain.