Cannot Communicate with Datasocket Servers on Private Networks

Question

I have not had the opportunity to confirm nor deny the reports I'm getting about an application that I've built and distributed, but let me give you the details and I'd like to know if anyone has heard of this and might be able to give me some words of wisdom.
I have a rather simple program that uses a datasocket server to publish data that multiple client computers read (the clients are ONLY readers, and the host is the only writer).  The computers are all connected to a 4-port router, and the computers within the network can ping each other, FTP files back and forth to each other, and can also share Windows shares (they're all WinXP computers).  These computers have their firewalls completely turned off, and the router has no built-in firewall; my contacts have tested 4 different models of routers and get the same behavior on all 4 of them. 
Anyway, on a closed network where the router is NOT plugged into the internet, the client machines cannot communicate with the Datasocket server via dstp (or any mechanism thereof).  To communicate with the datasocket server, I use the raw IP address of the computer, like:  dstp://192.168.1.100/namespace/variable.  When the software attempts to make the connection, errors saying the datasocket server/variable does not exist spew out.  Remember that machines on this network can ping each other, communicate with each other via windows shares, and can even FTP files back and forth.
Once a live internet connection is plugged into the router, everything seems to spring to life.  All communication with the datasocket server immediately begins working (when it is attempted to connect again). 
I initially thought the problem might be related to a stale DNS server entry in the network configuration, but even after resetting the router (so that the router has default values and points to itself for DNS lookups) the problem still exists.  They've rebooted the computers connected to the router NOT on the internet to make sure all the new network values are taken, and still no luck.
Has anyone run into this and found a workaround?  Unfortunately where we need to set up this network is not near a live internet connection, and we're beginning to be SOL if we cannot find an adequate workaround.
Thanks!
-Danny

Answer 1

Danny,
This definitely seems like an issue with your router/configuration -- unfortunately after searching around I don't have much to offer, but here are a few thoughts --
Is it possible that the router is somehow dependent on its uplink port being connected? Have you searched the router's configuration utility/KnowledgeBase for anything that sounds like this issue?  Could it be possible to disable this?  Is it possible that some application, whether on the router itself or an application on your client PCs is constantly trying to ping something on the internet and hogging bandwidth because a connection cannot be established?
I was a little confused by these two statements which seem conflicting:
"When the software attempts to make the connection, errors saying the datasocket server/variable does not exist spew out."
"I am usually able to connect to the datasocket
server, but my data coming from the datasocket server is VERY slow and
very spotty.  My data becomes stale and is not refreshed any more."
Are you still getting errors as mentioned in the first statement? If not, what changed?
One thing that may be of use is to use a low level traffic monitoring utility like Ethereal and compare packet types and volumes when the Internet is connected and when it is not.
Message Edited by Doug M on 12-15-2006 04:28 PM
Doug M
Applications Engineer
National Instruments
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