Dear readers,

I have a process A that connects to a remote server using standard TCP/IP stuff like: 
     sid = socket(AF_INET, SOCK_STREAM, 0);
     .....
     connect (sid, .....)
     ....
     send(sid, ....)
     ....
     recv(sid,...)

It runs  in a seperate thread and does a kind of ping to make sure the  remote side is sane (and also send some status 
info).
 
I also have a local server process B that listens for a remote connection 
and gets a file descriptor when it accepts the connection by means of the accept routine. This fd is then used to send 
and receive to the remote side. When I share this fd with process A, process A can also send to the remote side just 
like process B. This file sharing mechanism is discussed in the article by Thomas Fletcher.

Summarizing, process A has now two connections open to the remote side. This mechanism just described works the first 
time when running. However, when the remote connection to process B is lost and re-established, re-sharing the new file 
descriptor with process A, then  process A will give me back an invalid shared file descriptor (-1). I haven't got a 
clue why. 

I did some experiments.
1) For process A, when I leave out the thread that connects to the remote side the file sharing mechanism keeps working 
no matter how many times I disconnect and re-establish a connection with server process B

For process A, when I create the socket mis-using the flag SO_REUSEADDR like this:
     sid = socket(AF_INET, SOCK_STREAM |  SO_REUSEADDR , 0);
the file sharing mechanism also keeps working. Unfortunatly now I can not connect to the remote side any more with this 
socket. 

Is there anyone who has a clue whats going on here? I realize I've entered the dungeons of network programming -:)

Thanks Wim