Rules that are written in the terminal, are lost after system restart.
For more info, please refer the "Rules persistency" chapter in Reference.
Graph taken from here.
iptables command structure:
iptables commands:
If -n flag is used, the numeric values will be printed.
For example, ssh port will be printed as 22.
This prevents alot on DNS lookups.
List filter table (filter is the default table).
(nv for numeric and verbose)
sudo iptables -nvL
List specific table (nat in this example).
(nv for numeric and verbose)
sudo iptables -nvL -t nat
Remove all rules from all chains (of the default filter table).
sudo iptables -F
Remove all rules from input chain (of the default filter table).
sudo iptables -F INPUT
Each packet that doesn't maches any rule will have the default policy.
In the example below, all the packets in FARWARD chain will be dropped.
sudo iptables -P FARWARD DROP