why would Linode port number make a difference to Arduino?

We have been running a custom server on our Linode at port 8000 for over a year now. Most of the users access this server with client software running on a Windows, Mac or Linux OS. We haven't experienced any problems.

Recently we began a project to port this protocol to a deeply embedded Arduino device. The Arduino is the client; our Linode hosts the server. However we are noticing very frequent timeouts from the Arduino while it tries connect to port 8000. We have run an extensive matrix of experiments including knocking down Apache and running our server on port 80. Arduino connects perfectly with port 80. Best we can tell the actual port number is the variable which determines whether or not the Arduino can reliably connect to the Linode.

While the source of this "problem" may well reside in the Arduino library, I thought I would ask this forum if any one can think of a reason why Linode port 80 and port 8000 would be different. ie. are their subtle timing differences which might be spooking the Arduino library to go down a timeout branch?

Thanks in advance for your help.


3 Replies

Shouldn't be a difference, although many networks treat traffic differently depending on port. What does tcpdump show on each end?

You might try a different standard port such as 443 (used for SSL connections) as a test - that port might also get you past a few more outgoing firewalls on the client side. The problem might be whether the port number is above or below 1024, so you could test 1023 vs. 1025.


Port 8000 is not a good choice to use as MANY firewalls, security devices and ISPs block it or rate limit it for several reasons

  • Shoutcast/Icecast servers use ports 8000-8050;

  • Several worms use port 8000..

For some more items that use 8000, http://www.speedguide.net/port.php?port=8000


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