Open port using iptables

To open a required port you have to know the basic information. 

1) Service name ( ssh,ftp,etc...)

2) port number ( 22,25, etc...)

3) tcp port or udp port (tcp or udp)

Example : To enable ssh access to your Server from anywhere

#iptables -A allowed -p tcp -dport 22 -s 0/0 -j ACCEPT

#iptables -A allowed -p udp -dport 22 -s 0/0 -j ACCEPT