Cant connect over local WiFi network to Librem 13v4 running Byzantium

I have a L13v4 with an app called MusicBrainz Picard installed. There is a function on this program where you can use an Android phone on the same WiFi network to pass barcodes to the program using the IP address of the laptop and a listening port. The port operates correctly when self-interrogated by the laptop (eg. using IP:port in the browser), but not when trying to connect from another device (2 Android devices and one Windows PC failed to connect). It short, it’s acting like there’s a firewall preventing the devices from connecting, but I can’t find anything operating in PureOS that I can identify as an active firewall or anything like it. Any ideas?

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Yes, it does sound like a firewall.

Sanity check though … do you get to choose the port number? Regardless, what is the port number?

Use ss -lntp to confirm the details of what is listening on the port and on what IP address.

Check what firewall software is even installed. e.g. ufw or firewalld

If the iptables command exists then iptables -L

I’m assuming IPv4. Confirm?

You should also confirm lower level network connectivity i.e. can you ping the Librem 13 from the Windows PC?

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I am using IPv4
I can choose the port number. Default is 8000, it’s currently 1024 because i didn’t change it back after trying it.
ss -lntp confirms that Picard is listening on 1024
firewalld appears to be installed, but ufw is not. I can’t figure out how to check if it is doing anything.
iptables -L gives me:

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

I’ll try pinging in the morning. The Windows PC is currently shut down.

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Then the next step would be to see whether it is running.

sudo systemctl status firewalld

and if it is then you might temporarily stop it in order to verify that that is the cause of the problem. I’m not knowledgeable on configuring firewalld. Maybe try: How to Configure Firewalld on a Web Server and in particular the section on Manage Ports.

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Yes, when I checked, firewalld was up and running, and it’s started by default during boot. I was able to ping my L13 from my Windows machine on the network while firewalld was working, but I wasn’t able to access the port. I stopped firewalld, and that allowed the connection I was trying to make to occur between my Android app and the desktop app. Starting was harder, I had to reboot. So it looks like I will need to learn port configuration!