are sent during timeout period, then remote peer is considered to be
dead. Timeout option should be synchronized both for server and client.
-If there were no packets at all during third part of timeout, then
+If there were no packets at all during fourth part of timeout, then
special heartbeat packet is sent. So VPN connection should be alive all
the time, even if there is no traffic in corresponding TAP interfaces.
@strong{Beware}: this consumes traffic.
Stale peers and handshake states are cleaned up every timeout period.
+
+This applies to TCP connections too: relatively much time can pass until
+we understand that remote TCP peer is suddenly died and did not
+normally terminate connection.