Configure iPad on cable modem ethernet network

Question

I am having trouble connecting an iPad to other computers on my local network, which is provided by a cable modem. The cable modem has a number of static IPs available to it. I have a linux computer plugged into the modem and it has one of these static IPs which is manually configured.

I know the computer can talk to devices on the local network. For example, I have a printer that only has a local address which is 10.1.10.190 and the linux computer can print to that printer by sending to that local address.

When I connect the iPad to the cable modem via a cable the ethernet interface says that it has a IP address of 10.1.10.161 (and several automatically discovered IPv6 addresses). The browser on the IP works, so I know it is has network connectivity.

The problem is that when I use KDE Connect, the computer and iPad are not finding each other. Even if I manually enter the computers IPv4 address (96.79.X.X) in KDE Connect it still does not find the computer.

I thought if I could find the computers local address (10.1.10.X) then I could manually put that in KDE Connect but I do not know how to find out that local address on Linux. If I do "sudo ip address" for example, it just shows the IPv4 address, not any local address.

Note that if I do a command like "netcat -z -v 10.1.10.161 1716" on the linux machine, then I get the answer "ipad.hsd1.nh.comcast.net [10.1.10.161] 1716 (xmsg) open" so the linux machine can apparently definitely access the iPad.

What is my next move?

Answer 1

I figured this out. Apparently I had a firewall active on the linux box (which I had forgot about) and KDEConnect requires bidirectional udp to work and discover other machines.

The way I figured this out was that I used the command:

sudo iptables -L -v

which revealed that a ufw firewall was active. I verified this by giving the command:

sudo ufw status 

Which said that ufw was "active" and listed the rules that ufw was using. I added rules that allowed use of the udp ports that kde connect uses, then restarted KDE Connect on the linux box and the machines then recognized each other.