Iptables

Check if the server had install Iptables or not

rpm -q iptables

If Haven't install, install it by using

yum install iptables

Rules

This is the standard rule for all the server

iptables -A INPUT -i lo -j ACCEPT
iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A INPUT -p tcp --dport 22 -j ACCEPT

iptables -A INPUT -p icmp --icmp-type 8 -j ACCEPT

iptables -P INPUT DROP

save the iptables rules so that each time iptables start will refer back to this rule

/etc/init.d/iptables save

remember to save every time you finalize your rules
start/restart the iptables after save

/etc/init.d/iptables start

Check open port

Use nmap to check open port, install it via yum or use other server which have nmap installed to check open port by

nmap "destination"

example

nmap 172.30.10.230

you can use this link to check each description for each port
http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers

HowTo

add specific port into Iptables. This will add rule to the end of the selected chain

iptables -A [CHAIN] -p tcp --dport [port number] -j [ACCEPT/DROP]

example

iptables -A INPUT -p tcp --dport 443 -j ACCEPT
iptables -A OUTPUT -p tcp --dport 80 -j DROP

This will allow port 443 connection to come in and the 2nd rule will block http connection to go out

add port to a specific rule number. So if the rule number is 1, the rule inserted will be taking no.1 and push default no.1 rule to no.2

iptables -I [CHAIN] [rule number] -p tcp --dport [port number] -j [ACCEPT/DROP] 

example

iptables -I INPUT 1 -p tcp --dport 22 -j ACCEPT

This will make allow connection to come in from port 22 as the first rule

delete specific rules

iptables -D [CHAIN] [rule number]

list out all the rules

iptables -L