and sent to remote server, that writes them to his interface, and vice
versa. Client and server use pre-shared authentication key (PSK).
Because of stateless UDP nature, after some timeout of inactivity peers
-forget about each other and have to retry handshake process again. As a
-rule, there are enough time-to-time traffic in ordinary Ethernet
-networks to heartbeat connection.
+forget about each other and have to retry handshake process again,
+therefore background heartbeat process will be ran.
Handshake is used to mutually authenticate peers, exchange common secret
per-session encryption key and checks UDP transport availability.