Very Computer

I am encountering some strange problems with the connect() routine on
IBM RS/6000 running AIX 3.2.

Before calling connect(), my program (client) calls bind() to bind the
socket to a specified port number and local host.  The program will
connect to another specified port number on which another program
(server) is listening.  What I need is the listening program will call
accept() and extract the port number bound to the connecting socket.

When I terminate the client while the server is still running, and then
restart the client, the connect() routine returns an EADDRINUSE error.
The funny thing is that bind() returns no error (I set the socket option
for SO_REUSEADDR).  However, after a number of EADDRINUSE error, the
connect() routine will eventually be successful.  On RS/6000, I have
tested that if the client is restarted 55 seconds after termination,
connect() is always successful.  But is I restart the client at 50
seconds after termination, I will get EADDRINUSE at the connect()
routine.

Has anyone encountered the same problem or experienced similar situation
before?  Would like to know what is the cause to this problem and how to
go about solving it.  I suspect some kind of daemon for the network card
running at pre-defined time interval in releasing network resources
(ie., port numbers) maybe the reason but is not certain.

Thanks in advance to any reply.

 Tan> I am encountering some strange problems with the connect()
 Tan> routine on IBM RS/6000 running AIX 3.2.

 Tan> Before calling connect(), my program (client) calls bind() to
 Tan> bind the socket to a specified port number and local host.  The
 Tan> program will connect to another specified port number on which
 Tan> another program (server) is listening.  What I need is the
 Tan> listening program will call accept() and extract the port number
 Tan> bound to the connecting socket.

Calling bind() before connect() has all sorts of pitfalls, one of which
has bitten you. There are very, very few cases where a client program
should be using a fixed port number. See the socket FAQ for a fuller
explanation.

 Tan> When I terminate the client while the server is still running,
 Tan> and then restart the client, the connect() routine returns an
 Tan> EADDRINUSE error.  The funny thing is that bind() returns no
 Tan> error (I set the socket option for SO_REUSEADDR).  However,
 Tan> after a number of EADDRINUSE error, the connect() routine will
 Tan> eventually be successful.  On RS/6000, I have tested that if the
 Tan> client is restarted 55 seconds after termination, connect() is
 Tan> always successful.  But is I restart the client at 50 seconds
 Tan> after termination, I will get EADDRINUSE at the connect()
 Tan> routine.

What's happening here is that the original connection remains in TIME_WAIT
state for a time after being closed. Since the 5-tuple (protocol, local
address, local port, remote address, remote port) must be unique at all
times, the attempt to establish a connection between the same ports fails.
Solution: don't use a fixed port number for the client - let the system
pick one for you.

 Tan> Has anyone encountered the same problem or experienced similar
 Tan> situation before?  Would like to know what is the cause to this
 Tan> problem and how to go about solving it.  I suspect some kind of
 Tan> daemon for the network card running at pre-defined time interval
 Tan> in releasing network resources (ie., port numbers) maybe the
 Tan> reason but is not certain.

 Tan> Thanks in advance to any reply.

The unix-socket-faq is regularly posted here and in comp.answers, and may
also be found at:

  http://www.auroraonline.com/sock-faq
  http://kipper.york.ac.uk/~vic/sock-faq
  ftp://rtfm.mit.edu/pub/usenet/news.answers/unix-faq/socket

Hope this helps

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