Check wich policies are configured

iptables -L

clint@stbkp01 ~]$ sudo iptables -L | grep policy
[sudo] password for clint: 
Chain INPUT (policy ACCEPT)
Chain FORWARD (policy ACCEPT)
Chain OUTPUT (policy ACCEPT)

Connection

ACCEPT
DROP - ping with lost
REJECT - destination port unreachable, loss 0

iptables -A - add rule to the chain

iptables -F - delete all rules

Source of the trafic

iptables -A INPUT -s 120.8.7.5 -j DROP

add port block

iptables -A -p tcp --dport ssh -s 120.8.7.5 -j DROP

save config

sudo /sbin/iptables-save

=sbin/service iptables save

Firewall-cmd

Installed like daemon. New rules are added without restart uses firewall-cmd or firewall-config (grafic) utility

Status: systemctl status firewalld

[clint@stbkp01 ~]$ sudo firewall-cmd --permanent --zone=public --add-port=8088/tcp
success
[clint@stbkp01 ~]$ sudo firewall-cmd --reload
success
[clint@stbkp01 ~]$ sudo systemctl restart firewalld
[clint@stbkp01 ~]$ sudo firewall-cmd --zone=public --list-all
public
  target: default
  icmp-block-inversion: no
  interfaces: 
  sources: 
  services: dhcpv6-client ssh
  ports: 8088/tcp
  protocols: 
  masquerade: no
  forward-ports: 
  source-ports: 
  icmp-blocks: 
  rich rules: 

[clint@stbkp01 ~]$

Cron

SELinux