FortiGate is operating in NAT mode and is configured with two virtual LAN (VLAN) subinterfaces added to the same physical interface. In this scenario, which statement about VLAN IDs is true?
A.
The two VLAN subinterfaces can have the same VLAN ID only if they belong to different VDOMs.
B.
The two VLAN subinterfaces must have different VLAN IDs.
C.
The two VLAN subinterfaces can have the same VLAN ID only if they have IP addresses in the same subnet.
D.
The two VLAN subinterfaces can have the same VLAN ID only if they have IP addresses in different subnets.
Answer A is only correct if we use different hardware interfaces in different VDOMs.
Same VLAN ID, different VDOMs, same hardware interface - not valid.
Same VLAN ID, different VDOMs, different hardware interfaces - valid
Answer is: A and B
Why A is right, you can see here: https://community.fortinet.com/t5/FortiGate/Technical-Note-How-to-use-emac-vlan-to-share-the-same-VLAN/ta-p/192843?externalID=FD43883
I'm totally sure that answer is B, but if we talk about "VDOMS" each VDOM is a different "VFR" that means, you can have in the same physical interface, multiples vlans, with the same VLAN ID, but.. in different VDOM's vlan30 -> vdom root , vlan40 -> vdom user, both interfaces on the same port1 physical interface.
If multi vdoms in multi vlans under 1 interface scheme-> A is also a Correct Answer.
Reference: Page 156, Fortigate Infrastructure 7.0 new version!
B - The same VLAN number cannot be configured twice on the same physical interface
https://community.fortinet.com/t5/FortiGate/Technical-Tip-rules-about-VLAN-configuration-and-VDOM-interface/ta-p/197640
I understand that it is because you can assign interfaces to different vdoms, but not to the subinterfaces, if you have a physical interface assigned to the VDOM Root for example, all the subinterfaces also belong to that vdom
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TJBIII
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