It is recommended that you use 'internet Connection Sharing' (ICS) instead of NIC for all RNDIS based tethering.
However in order to debug the NIC mode, please read below:
1. Verify that your UE's Internet tethering option is enabled. For Android release Froyo and higher, Internet tethering can be enabled in the Wireless Networks menu of the UE.
2. When connecting the UE to the Laptop via USB, a RNDIS adapater will appear and mapped to a new local area connection. Once tethering is enabled, the RNDIS disappears and a new RNDIS with a different name appears, mapped to yet another new local area connection. The IP address assigned by the UE to the 'tether disabled' RNDIS/local area connection will be different from the Ip address assigned to the 'tether enabled' RNDIS/local area connection. The 'tether disabled' RNDIS/local area connection will only show an IP address without a gateway. Spirent Data Client will therefore not find the appropriate 0.0.0.0 route in the routing table and report that the IP address has not been assigned.
3. Verify that your tethering option is enabled and that the 'tether enabled' RNDIS/local area connection has a proper IP address + IP gateway address pair assigned