The syntax to add an iptables rule is as shown below.
# iptables -I INPUT [line number] -s [ip address or subnet] -j ACCEPT
For example to add a new rule at line number 2 to allow subnet 192.168.0.0/24.
# iptables -I INPUT 2 -s 192.168.0.0/24 -j ACCEPT
Saving iptable rules
After configuring the iptables rules from the command line, it is required to save the iptable rules. It is important to save the list of iptable rules to make them persist across reboots or restart of iptable service.
# service iptables save