Line loopback enables frames received on a network port to be retransmitted to the same network port without involving the host CPU.
Frames are looped back to the same port without being modified. This includes the FCS which is not recalculated.
The line loopback functionality and the filtering/capturing functionality can be used independently of each other. A port with line loopback enabled can at the same time be used to capture, for instance, all received IP frames.
A port cannot be used for host transmission while line loopback is enabled on that port.
The line loopback functionality can be enabled by using the config tool or by using the NTAPI.