> I was not able to ping google.com: no dns address found so it just hung.
If you can, for instance, `ping 8.8.8.8`, maybe it's just a DNS
misconfiguration. You can try setting the IP address of the modem
(something like 192.168.0.1 or 10.0.0.1, for instance) as DNS.
I finally removed the existing firewalld from the system and the system now works fine. Then I installed ufw and am using it.
Note the system was originally Debian 9 (maybe 8) and has been upgraded through the awkward 9-to-10 change and on to 11.
Anyhow, magically it works now. Thanks for your patient help.
Blessings,
-Tom