With iptables. There is a couple of ways to do iptables. Inserting or appending is the two categories. If you made mistakes you can be locked out the system. THOUGH:

-A RH-Firewall-1-INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

before any DROP/REJECT rules, you'll be fine Play dumb and use Red Hat's GUI if you are a newbie:

up2date --install system-config-securitylevel

system-config-securitylevel

service iptables status

Edit the : /etc/sysconfig/iptables When you're comfortable. E.g. -A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp -s 61.9.136.168 --dport 1521 -j ACCEPT Allows access only to my IP for the Oracle port 1521.

[hendry@server sysconfig]$ sudo cat iptables
# Firewall configuration written by system-config-securitylevel
# Manual customization of this file is not recommended.
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:RH-Firewall-1-INPUT - [0:0]
-A INPUT -j RH-Firewall-1-INPUT
-A FORWARD -j RH-Firewall-1-INPUT
-A RH-Firewall-1-INPUT -i lo -j ACCEPT
-A RH-Firewall-1-INPUT -p icmp --icmp-type any -j ACCEPT
-A RH-Firewall-1-INPUT -p 50 -j ACCEPT
-A RH-Firewall-1-INPUT -p 51 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp --dport 5353 -d 224.0.0.251 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp -m udp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 443 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 10001 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 1521 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
COMMIT

TEST YOUR FIREWALL! netcat and nmap In RH to restart the service:

sudo service iptables restart

And check:

iptables -vnxL
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