[CentOS] Socket behavior change from 6.5 to 6.6

Sat Jan 17 00:15:37 UTC 2015
Greg Lindahl <lindahl at pbm.com>

On Fri, Jan 16, 2015 at 01:23:56PM -0600, Les Mikesell wrote:

> And, without keepalives enabled,
> you still won't get an error on the write.

No, if the other end is up after a reboot, you'll get an immediate
error and socket close.

That's assuming the window isn't full; if it is, you'll have to wait
until a zero-window probe.

App level ping-ponging is the way to make sure TCP connections are
actually alive. I've never seen a portable system use keepalives for
that, due to the >= 2 hour default and the lack of a portable way to
configure the time.

There sure are a lot of mutually-conflicting opinions flying in this
thread. I learned this stuff by studying how IRC uses
application-level ping-pong, and have encountered and used this info
repeatedly in the years since.

-- greg