I've got a problem that is defying my ability to find it. I have a product
that uses sendto() to send UDP messages (datagrams). At one and perhaps two
z/OS 1.12 customers I have seen a problem in which what appear to be
perfectly good sendto()'s send a datagram that never arrives at its
destination. (Of course, the lack of error feedback is a known
characteristic of UDP.)

Version x.1 of my product does not exhibit this behavior. Version x.2 does.
There is relatively little difference between how the two issue sendto(). I
have never seen the problem on my development machine, including under z/OS
1.12.

It is definitely not a firewall or other external issue because Version x.1
works fine. You bring it down and bring Version x.2 up with the same
parameters and it works for a little while and then 100% of the messages
start disappearing. You bring it down and bring x.1 back up and all is well.
Similar TCP/IP code does not seem to have the same problem.

Yes, obviously it could be your basic program bug and I am of course working
the heck out of that angle. I'm not asking this list to debug code it has
not seen. The code is way too complex to post here meaningfully.

But does this problem ring a bell with anyone? I am not the most skilled in
the world at searching for APARs. Does anyone else want to spend 5 minutes
and see if you can find anything?

Thanks much,
Charles 

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