I hope you can help me :)

I am setting up a credit card terminal in my store network. (It‘s just a mobile LTE Router with a static IP address and a switch)

The payment processing provider requires me to allow traffic to their specific IP adresses and ports in my network in order for the terminal to work.

They gave me a list of several IP adresses and corresponing ports:


I tested the connections with telnet and everything worked except the connection on two ports. 3443 and 4443

I tested the these ports with Wireshark and it gave me a tcp retransmission feedback!

Now I am stuck. What do I have to do that my network can establish a connection to said adress and ports? Does it have something to do with my ISP?

Best, Max

  • Do you have any intentional lockdowns on your network? Do you have any actual issues with the terminal? Just because they want to have traffic allowed does not mean that there is actually anything there. And did it say that it was TCP traffic to those ports? if UDP you will not be able to establish a TCP connection to that port. If something does not work, contact their support.
    – NiKiZe
    Aug 12, 2021 at 9:06
  • Hey! Thanks for your reply. I have not yet received the terminal. I wanted to make sure the connections are fine before they come and install the terminal. I do not have any restrictions on my side of the network. So the failed telnet connection to this port doesn't mean that the connection is closed necessarily ?
    – maxig
    Aug 12, 2021 at 9:15
  • Many networks, especially consumer grade, is open by default, and nothing is usually needed. However many company networks are closed down, that is why they include that information. But again, it should say if it is TCP or UDP and on which port. (in your case never mind, and just test, contact their support if there is issues)
    – NiKiZe
    Aug 12, 2021 at 10:18


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