@CB , Thank you for your question.
You can delete a network interface as long as it's not attached to a virtual machine. If a network interface is attached to a virtual machine, you must first place the virtual machine in the stopped (deallocated) state, then detach the network interface from the virtual machine. To detach a network interface from a virtual machine, complete the steps in Detach a network interface from a virtual machine. You cannot detach a network interface from a virtual machine if it's the only network interface attached to the virtual machine however. A virtual machine must always have at least one network interface attached to it. Deleting a virtual machine detaches all network interfaces attached to it, but does not delete the network interfaces.
When you delete a network interface, any MAC or IP addresses assigned to it are released.
Hence, while it is possible to Add Network Interfaces to or remove from Azure Virtual Machines the constraints mentioned here must be followed and must be performed with user intervention. Only a VM deallocation or stop does not suffice to change the NIC association.
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Hope this helps.
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