RE: Socket Question - Host Refusing Connection

Scott, Chris, 

Thanks for your help.  I have bumped the backlog parameter up to 1000. 
I'll see if that helps.  This doesn't happen very often.    I have 
verified that the listener job was active.  The app runs on our internal 
network so the traffic doesn't hit the firewall.  It is likely the backlog 
threshold being exceeded.

Thanks again. 

Mark Garton
O'Reilly Auto Parts


date: Thu, 4 Nov 2004 11:32:22 -0600 (CST)
from: Scott Klement <midrange-l@xxxxxxxxxxxxxxxx>
subject: Re: Socket Question - Host Refusing Connection


> Is there anything else that can cause this error?  I have the
> backlog parameter set to 400 with 1000 clients running this application.
> It doesn't seem likely that it would exceed a backlog of 400.

Seems to me that you probably want to set the backlog to 1000. Maybe I'm
just confused, but if you have 1000 clients, it would seem weird to set a
400 client limit.

You get a "connection refused" message whenever the system isn't
listening.  So, like you said, filling up the backlog would do it.  Also,
if there's no socket listening, you'd get the error.  (For example, if you
close() the listener socket, or if the program isn't running...)

It's also possible (but unusual) for a firewall to issue this message when
it's blocking a port.

> Is there any way I can see what is happening on the host besides adding
> logging to my listener program?  Thanks.

Run a network sniffer, or communications trace type of thing...  But I
don't really think that'll tell you anything.  What you'll find out is
that an ICMP message is sent back that says "connection refused" -- not
very helpful, you already know that!

You could also use NETSTAT on the host to see how many connections are
active at the time that this happens.  My guess is it's happening when you
hit the 401st active connection.