On Tue, 2021-07-27 at 16:43 -0400, H wrote: > > Running CentOS 7. I was under the impression - seemingly mistaken - > > that by adding a rule to /etc/hosts.deny such as ALL: aaa.bbb.ccc.* > > would ban all attempts from that network segment to connect to the > > server, ie before fail2ban would (eventually) ban connection > > attempts. > > This, however, does not seem correct and I could use a pointer to > correct my misunderstanding. How is hosts.deny used and what have I > missed? hosts.deny is only used by specific programs that use TCP wrappers. It is not a general "deny this host access". Also note that fail2ban operates on individual hosts, not subnets. > > Is it necessary to run: > > iptables -I INPUT -s aaa.bbb.ccc.0/24 -j DROP > > to drop incoming connection attempts from that subnet? > If you use iptables yes, probably. Firewalld has a specific drop zone that you can use: firewall-cmd --zone=drop --add-source=aaa.bbb.ccc.0/24 (with suitable --permanent flag if you want it permanent). P.