Re: TCP Keepalive not working?

On Mon, 8 Jul 2002, Patrick Townsend wrote:
>
> Have any of you TCP gurus gotten the TCP KeepAlive function to work?
>

I hadn't previously used this option with a server socket, but
I wrote a quickie test program, and fired up the ol' packet sniffer, and
it appears to work.

Here are some important notes:

>From IBM's manual for setsockopt():

     "For sockets that use a connection-oriented transport service, IP
      options  that are set using setsockopt() are only used if they are
      set prior to a connect() being issued. After the connection is
      established, any IP options that the user sets are ignored."

As usual, IBM is vague.  We're not calling connect(), but it should still
work as long as we set the socket option before the socket is connected to
the other end.   Of course, that creates a new problem, because accept()
makes a new socket and immediately connects it :)    Fortunately, in
the docs for accept() we see this:

     "The following are inherited by the descriptor returned by the
      accept() call:
        - All socket options with a level of SOL_SOCKET."

So, what you actually want to do, is do the setsockopt() on your
"listener" socket (the one that you use as an argument to bind(), listen()
and accept())  then the client's socket will inherit it.

That's what I did... and it worked for me.  To be precise, I called
setsockopt() immediately after calling socket() for the listener socket.

> But it never works. The TCP attributes have been changed for keepalive
> every 60 seconds. A sniffer trace shows that the AS/400 is not sending
> out any frames.

Make sure that when you do a CHGTCPA TCPKEEPALV() that you understand that
the times are in MINUTES not seconds! :)   I.e. for a 60-second, you'd
do CHGTCPA TCPKEEPALV(1).

If you do TCPKEEPALV(60), it'll send them once per hour, which probably
isn't what you wanted ;)

Good luck!