How to block someone's IP
From Kolmisoft Wiki
First of all install iptables if needed:
yum -y install iptables
To block incoming IP, use this command:
iptables -A INPUT -s IP -j DROP
iptables -A INPUT -s 220.127.116.11 -j DROP
To save the rules (On Centos), run:
Question: I want allow only specified IPs to my server and dissallow any other connections, how I could do that?
First of all enter all friendly ips:
iptables -A INPUT -s friendlyip. -j ACCEPT iptables -A INPUT -s another.friendly.ip -j ACCEPT iptables -A INPUT -s 127.0.0.1 -j ACCEPT # yes, accept connections from localhost.
And the most end enter:
iptables -A INPUT -s 0/0 -j DROP
If in future you will want to add some more ips, just first reject rule with DROP, and some friendly ip and then apply DROP rule again.
Very important: Don't forget to add ISP/router to your friendly ip address list!!!
 How to unblock IP
Search for the IP under /etc/sysconfig/iptables:
grep 18.104.22.168 /etc/sysconfig/iptables
This would give the following output:
-A INPUT -s 22.214.171.124 -j DROP -A INPUT -s 126.96.36.199 -j ACCEPT
Then you can delete the rule using the '-D' option in iptables:
iptables -D INPUT -s 188.8.131.52 -j DROP
Now IP 184.108.40.206 is unblocked.
 How to check all blocked IPs
iptables -L -n
 How to check if IP is blocked
iptables -L -n | grep IP