Setting keepalive ensures that idle connections will eventually be
closed. In userspace mode, any application configured TCP keepalive is
effectively swallowed by the host kernel, and is not easy to detect.
Failure to close connections when a peer tailscaled goes offline or
restarts may result in an otherwise indefinite connection for any
protocol endpoint that does not initiate new traffic.
This patch does not take any new opinion on a sensible default for the
keepalive timers, though as noted in the TODO, doing so likely deserves
further consideration.
Update #4522
Signed-off-by: James Tucker <james@tailscale.com>
1aa75b1c9e