KeepAlive
Specifies whether the system should send keepalive messages to
the other side. If they are sent, death of the connection or
crash of one of the machines will be properly noticed. However,
this means that connections will die if the route is down temporarily, and some people find it annoying. On the other hand,
if keepalives are not sent, sessions may hang indefinitely on the
server, leaving ``ghost'' users and consuming server resources.
The default is ``yes'' (to send keepalives), and the server will
notice if the network goes down or the client host reboots. This
avoids infinitely hanging sessions.
To disable keepalives, the value should be set to ``no'' in both
the server and the client configuration files.