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Old 02-01-2015, 09:26 PM   #1
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Registered: Jul 2013
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Unhappy What could be blocking incoming connections to my program?

Hi all,
I am brand new to Linux, playing around a bit with different things to see how I can use it in the future. Here is my problem:

I have written a simple program in Ada that works well on windows. It opens a TCP port (20000) and listens for incoming connections. I tried it on my internal network and it works well. I can connect from other windows machines and even from my Linux machine.

Now I moved the program to Linux and compiled it there. It starts ok and then listens for the connections. I can connect to it from that same Linux machine but not from any other machine on my network.

I checked the firewall status on Linux with ufw status and it is disabled. I also tried to add a rule to the iptables with
iptables -A INPUT -p tcp --dport 20000 -j ACCEPT

but still nothing. I can not connect from another machine on my network. I also tried to open a simple telnet connection from a windows machine and that too is blocked. I thought without the firewall all incoming connections would be allowed but obviously something is not working as I thought.

Any help would be greatly appreciated
Old 02-01-2015, 11:00 PM   #2
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Registered: Jul 2013
Posts: 9

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Well I found the solution myself and post it here in the case that somebody else needs an answer to the same problem.
It appears that the Addresses function in Gnat.Socket returns addresses in different order on windows and on Linux and my code grabbed the address that represents the localhost on Linux but the correct IPV4 address on Windows and therefore it was working on Windows, but on Linux it was now listening only on the loopback device.
So, never rely on the order in which addresses are returned by the socket library


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