It requires an Intel NIC which connects to both the main CPU and the ME at the same time. The ME has drivers for Intel NICs and a full TCP/IP stack. From the docs: https://software.intel.com/sites/manageability/AMT_Implement...

"The Intel 82566 Gigabit Network Connection identifies out-of-band (OOB) network traffic (traffic targeted to Intel AMT) and routes it to the Intel ME instead of to the CPU. Intel AMT traffic is identified by dedicated IANA-registered port numbers. The [southbridge] holds the filter definitions that are applied to incoming and outgoing in-band network traffic (the message traffic to and from the CPU). These include both internally-defined filters and the application filters..."