The user do not need to preconfigure the sub-interfaces. T&D does that when it makes the access and removes it when the access is released. In other words, during the initial access, T&D will discover all the interfaces currently configured on that particular VRF. Then, when we make the active access, we will build a sub-interface on the port connected to our probe using the first available VLAN from the testlink resource and then bind the sub-interface to the VRF