On Sat, 15 Jul 2023, Ming Kuang wrote:
Are you using any firewall rules? The phenomenon you describe is very much like a firewall blocking connections to these ports (you can connect out, can't connect in).
Thanks for the suggestion. The two Debian 9 machines have customising firewall rules set that I can see with iptables -L. Could well be the problem. However I have completely forgotten how and why the rules were set. I have more work to do. Thanks again, Roger
