[Command] iptables

 

[Clear all limits]
iptables -P INPUT ACCEPT
iptables -P FORWARD ACCEPT
iptables -P OUTPUT ACCEPT
iptables -t nat -F
iptables -t mangle -F
iptables -F
iptables -X

 

…and that should do it. iptables -nvL should produce this (or very similar) output:

 

Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target     prot opt in     out     source               destination
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target     prot opt in     out     source               destination
Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target     prot opt in     out     source               destination


Block Incoming Request From IP 1.2.3.4

The following command will drop any packet coming from the IP address 1.2.3.4:

 
/sbin/iptables -I INPUT -s {IP-HERE} -j DROP
/sbin/iptables -I INPUT -s 1.2.3.4 -j DROP
 

You can also specify an interface such as eth1 via which a packet was received:

 
/sbin/iptables -I INPUT -i {INTERFACE-NAME-HERE} -s {IP-HERE} -j DROP
/sbin/iptables -I INPUT -i eth1 -s 1.2.3.4 -j DROP
 

Please note that when the “!” argument is used before the interface name, the sense is inverted:

 
/sbin/iptables -I INPUT ! -i {INTERFACE-NAME-HERE} -s {IP-HERE} -j DROP
/sbin/iptables -I INPUT ! -i eth1 -s 1.2.3.4 -j DROP
 

If the interface name ends in a “+”, then any interface which begins with this name will match. If this option is omitted, any interface name will match:

 
/sbin/iptables -I INPUT  -i {INTERFACE-NAME-HERE}+ -s {IP-HERE} -j DROP
/sbin/iptables -I INPUT  -i br+ -s 1.2.3.4 -j DROP
 

You can replace -I INPUT (insert) with -A INPUT (append) rule as follows:

 
/sbin/iptables -A INPUT  -s 1.2.3.4 -j DROP
/sbin/iptables -i eth1 -A INPUT  -s 1.2.3.4 -j DROP
 
How Do I Block Subnet (xx.yy.zz.ww/ss)?

Use the following syntax to block 10.0.0.0/8 on eth1 public interface:
# /sbin/iptables -i eth1 -A INPUT -s 10.0.0.0/8 -j DROP

How Do I Block and Log Dropped IP Address Information?

You can turn on kernel logging of matching packets with LOG target as follows:
# /sbin/iptables -i eth1 -A INPUT -s 10.0.0.0/8 -j LOG --log-prefix "IP DROP SPOOF A:"
The next rule will actually drop the ip / subnet:
# /sbin/iptables -i eth1 -A INPUT -s 10.0.0.0/8 -j DROP

How Do I View Blocked IP Address?

Simply use the following command:
# /sbin/iptables -L -v
OR
# /sbin/iptables -L INPUT -v
OR
# /sbin/iptables -L INPUT -v -n
Sample outputs:

Chain INPUT (policy ACCEPT 3107K packets, 1847M bytes)
pkts bytes target     prot opt in     out     source               destination
0     0 DROP       all  --  br+    any     1.2.3.4              anywhere
0     0 DROP       all  --  !eth1  any     1.2.3.4              anywhere
0     0 DROP       all  --  !eth1  any     1.2.3.4              anywhere       
How Do I Search For Blocked IP Address?

Use the grep command as follows:
# /sbin/iptables -L INPUT -v -n | grep 1.2.3.4

How Do I Delete Blocked IP Address?

First, you need to display blocked IP address along with line number and other information, enter:
# iptables -L INPUT -n --line-numbers
# iptables -L INPUT -n --line-numbers | grep 1.2.3.4
Sample outputs:

num   pkts bytes target     prot opt in     out     source               destination
1        0     0 DROP       0    --  *      *       116.199.128.1        0.0.0.0/0
2        0     0 DROP       0    --  *      *       116.199.128.10       0.0.0.0/0
3        0     0 DROP       0    --  *      *       123.199.2.255        0.0.0.0/0

To delete line number 3 (123.199.2.255), enter:
# iptables -D INPUT 3
Verify the same, enter:
# iptables -L INPUT -v -n
You can also use the following syntax:
# iptables -D INPUT -s 1.2.3.4 -j DROP

How Do I Save Blocked IP Address?

If you are using Redhat / RHEL / CentOS / Fedora Linux, type the following command:
# iptables -D INPUT -s 1.2.3.4 -j DROP
##########################
#////// command to save iptables ///////#
##########################
# /sbin/service iptables save
# less /etc/sysconfig/iptables
# grep '1.2.3.4' /etc/sysconfig/iptables
For all other Linux distributions use the iptables-save command to dump the contents of an IP Table to a file:
# iptables-save > /root/myfirewall.conf
Please not that you need to run the ‘iptables-save’ or ‘service iptables save’ as soon as you add or delete the ip address.

A Note About Restoring Firewall

To restore your firewall use the iptables-restore command to restore IP Tables from a file called /root/myfirewall.conf, enter:
# iptables-restore < /root/myfirewall.conf

How Do I Block Large Number Of IP Address or Subnets?

You need to write a shell script as follows:


#!/bin/bash
_input="/root/blocked.ip.db"
IPT=/sbin/iptables
$IPT -N droplist
egrep -v "^#|^$" x | while IFS= read -r ip
do
$IPT -A droplist -i eth1 -s $ip -j LOG --log-prefix "IP BlockList "
$IPT -A droplist -i eth1 -s $ip -j DROP
done < "$_input"
# Drop it
$IPT -I INPUT -j droplist
$IPT -I OUTPUT -j droplist
$IPT -I FORWARD -j droplist