TCP Connection Keep-Alive direction

Question

When a connection have not received packets for a certain period of time (default 2 hours), it should send KEEP-ALIVE packets.

My question is, who will start sending KEEP-Alive packets, the client, server or both?

Answer 1

Either side will, assuming:

1. the OS is configured to do so (Linux, Windows)
2. the application configured the socket with SO_KEEPALIVE via setsockopt() (Linux, Windows).

If both sides have identical keepalive settings, then you'll see them both kick off a keepalive at nearly the same time.