So, I’m writing a program that will listen to dump1090 on port 30002, and it seems to work fine when it is connected to the internet. But when it is not on the network I’m getting a refused connection error in my program. Is there a setting in the default dump1090-fa program that doesn’t let these be active when there’s no internet connection?
No, dump1090 doesn’t do anything special based on network state.
I’d check that all of these are true when you’re running offline:
(a) dump1090 is actually running okay (check systemctl status etc)
(b) dump1090 is listening on 30002 (check netstat -nta)
(c) the host with dump1090 has the IP address that you expect (check ip addr etc)
(d) the host with your client has the IP address that you expect
(e) the DNS name your client is trying to connect to actually resolves to what’s in (c)
(f) connectivity between the two hosts is otherwise okay, e.g. you can still ssh
If you’re relying on a consumer-level router/modem to support the network, they can sometimes do unexpected things with DHCP & DNS (e.g. resolving everything to a single IP) when they don’t have an upstream connection.