Which of the following statements is false about BFD?

The asynchronous mode is the primary BFD operating mode.

In asynchronous mode, two systems periodically exchange BFD Control packets at the negotiated interval. If one system does not receive any BFD Control packets from the other within the detection interval, the BFD session is declared down.

The asynchronous mode does not support the echo function.

In demand mode, after a BFD session is set up, the system does not periodically send BFD Control packets.