Table of Contents

IPTables

List iptables Rules

iptables -L INPUT

To get the actual port numbers rather than use of port 

iptables -L -n INPUT

Delete iptables Rule

You can delete the rules based on their number and chain name. The following deletes the fourth rule on the list 

iptables -D INPUT 4

Save Rules

service iptables save

Reload Rules

service iptables restart

Block IP

iptables -A INPUT -s 1.2.3.4 -j DROP
service iptables save
service iptables restart

Unblock IP

Where you have run 

iptables -A INPUT -s 1.2.3.4 -j DROP

To undo this, run 

iptables -D INPUT -s 1.2.3.4 -j DROP

Block Subnet

iptables -I INPUT -s 43.229.0.0/255.255.0.0 -j DROP

Open a Single TCP Port

iptables -A INPUT -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT

Open a Single UDP Port

iptables -A INPUT -m state --state NEW -m udp -p udp--dport 80 -j ACCEPT

Limit Rule to Specific Ethernet Card

Add the following to the command being used to open the port. This example limits to rule to eth0. 

-i eth0

Insert Rule at Specific Point in Chain

To insert a rule at a specific point in a chain, modify the command from 

iptables -A INPUT

to 

iptables -I INPUT 5

where 5 should be replaced with the desired index.

Open a Range of Ports

This example opens ports 2121 to 2142 inclusive for TCP connections. 

iptables -A INPUT -p tcp -m state --state NEW -m tcp -m multiport --dports 2121:2142 -j ACCEPT

Prevent SSH Brute Force

iptables -A INPUT -p tcp --dport 22 -m state --state NEW -m recent --set  --name SSH -j ACCEPT
iptables -A INPUT -p tcp --dport 22 -m recent --update --seconds 60 --hitcount 4 --rttl  --name SSH -j LOG --log-prefix "SSH_brute_force "
iptables -A INPUT -p tcp --dport 22 -m recent --update --seconds 60  --hitcount 4 --rttl --name SSH -j DROP