Interfaces: Other Types: VXLAN needs additional constraints to prevent user error

[Monviech]

Important notices

Before you add a new report, we ask you kindly to acknowledge the following:

• I have read the contributing guide lines at https://github.com/opnsense/core/blob/master/CONTRIBUTING.md
• I am convinced that my issue is new after having checked both open and closed issues at https://github.com/opnsense/core/issues?q=is%3Aissue

Describe the bug

In the GUI in Interfaces: Other Types: VXLAN in the mask Edit VxLan the fields Remote address, Multicast group and Device can all be populated, even though that prevents the operating system from creating a working vxlan interface.

If you populate Remote address and Device (other than none) at the same time, dmesg shows this:
vxlan2: cannot initialize interface: can only specify interface with a group address

If you populate Remote address andMulticast group and Device at the same time, the vxlan interface comes up, but it's in multicast mode, ignoring the "Remote address" parameter:
vxlan vni 42 local 172.16.0.254:4789 group 239.0.0.1:4789

To Reproduce

1. Go to "Interfaces: Other Types: VXLAN" in "Edit VxLan"

• VNI: 42
• Source address: 172.16.0.254 (IP address of a firewall bound interface)
• Remote address: 172.16.0.186
• Multicast group: empty
• Device: LAN

2. Go to "Interfaces: Other Types: VXLAN" in "Edit VxLan"

• VNI: 43
• Source address: 172.16.0.254 (IP address of a firewall bound interface)
• Remote address: 172.16.0.186
• Multicast group: 239.0.0.1
• Device: LAN

Expected behavior

• When a Multicast group is set, it should be required to have Remote address empty, and the Device has to be NOT none
• When a Remote address is set, it should be required to have Multicast group empty, and the Device has to be none

Additional context

Heres the precise troubleshooting of my user error:

https://forum.opnsense.org/index.php?topic=36205.0

It was pretty hard to troubleshoot, so I think the additional constraints could be a valid addition.

Environment

Software version used and hardware type if relevant, e.g.:

OPNsense 23.7.4-amd64
FreeBSD 13.2-RELEASE-p3
OpenSSL 1.1.1v 1 Aug 2023

[AdSchellevis]

The number of validations are quite limited indeed, if you want to take a shot at this one, just let me know. For inspiration, the vip model (https://github.com/opnsense/core/blob/master/src/opnsense/mvc/app/models/OPNsense/Interfaces/Vip.php) contains quite some of them which are hard to catch with standard field validations (https://docs.opnsense.org/development/frontend/models_fieldtypes.html), custom ones (https://docs.opnsense.org/development/frontend/models_customfields.html) and/or constraints (https://docs.opnsense.org/development/frontend/models_constraints.html).

[Monviech]

Sure I'll give it a try. Thank you for the examples, I will look at them.