Oracle is powerful enterprise class database server and by default it listen on TCP port 1521. Following iptable rules allows incoming client request (open port 1521) for server IP address 202.54.1.20 :
iptables -A INPUT -p tcp -s 0/0 –sport 1024:65535 -d 202.54.1.20 –dport 1521 -m state –state NEW,ESTABLISHED -j ACCEPT

iptables -A OUTPUT -p tcp -s 202.54.1.20 –sport 1521 -d 0/0 –dport 1024:65535 -m state –state ESTABLISHED -j ACCEPT

Restrict access to Oracle database server from web server only. Following example allows Oracle database server access (202.54.1.20) from web server (202.54.1.50) only:
iptables -A INPUT -p tcp -s 202.54.1.50 –sport 1024:65535 -d 202.54.1.20 –dport 1521 -m state –state NEW,ESTABLISHED -j ACCEPT

iptables -A OUTPUT -p tcp -s 202.54.1.20 –sport 1521 -d 202.54.1.50 –dport 1024:65535 -m state –state ESTABLISHED -j ACCEPT

Allow outgoing Oracle client request from firewall host 202.54.1.20:
iptables -A OUTPUT -p tcp -s 202.54.1.20 –sport 1024:65535 -d 0/0 –dport 1521 -m state –state NEW,ESTABLISHED -j ACCEPT

iptables -A INPUT -p tcp -s 0/0 –sport 1521 -d 202.54.1.20 –dport 1024:65535 -m state –state ESTABLISHED -j ACCEPT