Duplexing is a performance option that lets you choose how the NIC sends and receives data packets over the network. The NIC can operate at full duplex only when connected to a full duplex 10BASE-T, 100BASE-TX switch, or to another full duplex NIC. � Auto (requires a full duplex NIC or switch with auto-negotiation capability). The NIC negotiates with the switch to send and receive packets at the highest rate. This is the default setting. If the switch does not provide auto-negotiation, the NIC runs at half duplex.