Linux Iptables block incoming access to selected or specific ip address

Posted on in Categories Debian Linux, Gentoo Linux, Iptables, Linux, Networking, RedHat/Fedora Linux, Security, Suse Linux, Ubuntu Linux last updated June 24, 2005

Sometime it is necessary to block incoming connection or traffic from specific remote host. iptables is administration tool for IPv4 packet filtering and NAT under Linux kernel. Following tip will help you to block attacker or spammers IP address.

How do I block specific incoming ip address?

Following iptable rule will drop incoming connection from host/IP 202.54.20.22:

iptables -A INPUT -s 202.54.20.22 -j DROP
iptables -A OUTPUT -d 202.54.20.22 -j DROP

A simple shell script to block lots of IP address

If you have lots of IP address use the following shell script:

A) Create a text file:

# vi /root/ip.blocked
Now append IP address:

# Ip address block  file
202.54.20.22
202.54.20.1/24
#65.66.36.87

B) Create a script as follows or add following script line to existing iptables shell script:

BLOCKDB=”/root/ip.blocked”
IPS=$(grep -Ev "^#" $BLOCKDB)
for i in $IPS
do
iptables -A INPUT -s $i -j DROP
iptables -A OUTPUT -d $i -j DROP
done

C) Save and close the file.

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin and a trainer for the Linux operating system/Unix shell scripting. He has worked with global clients and in various industries, including IT, education, defense and space research, and the nonprofit sector. Follow him on Twitter, Facebook, Google+.

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19 comment

  2. Cool, I’ve been running my own custom drop list I have honed over the years. Too much hacking. I block international access to domestic business servers whenever possible. I’m tired of those log files filled up with password guessing Asia. It works fantastic if one does not need access to international.

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  3. My blockiplist is text exactly like yours, but my script is different and I can’t recall why I did it this way, I hope it’s right, but it seems to work.
    ————
    for i in `cat /etc/blockiplist|grep -v “#”`
    do
    ADDR=$i
    /sbin/iptables -t filter -I INPUT -s $ADDR -j DROP
    /sbin/iptables -t filter -I OUTPUT -s $ADDR -j DROP
    /sbin/iptables -t filter -I FORWARD -s $ADDR -j DROP
    /sbin/iptables -t filter -I INPUT -d $ADDR -j REJECT
    /sbin/iptables -t filter -I OUTPUT -d $ADDR -j REJECT
    /sbin/iptables -t filter -I FORWARD -d $ADDR -j REJECT
    echo “Block ALL INPUT from ” $ADDR ” net DROPPED.”
    done
    —————–

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  5. Sir,

    In my company we are using Redhat Linux(15 EL) server for proxy settings, i need the command for blocking some particular ip’s not to use the internet & the same thing i need to release them to use internet, pls help me…………

    Reply Report comment

  9. Thanks for the information. I want to ask if it is possible to block absolutely EVERY single IP on the web except for a particular one on my home network (192.168.2.102) ?!

    How to do that ?!

    Apache can do this (for the http protocol) but it looks like the ftp server allows everyone in.

    I want to block all IP’s except that one mentioned above.

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  10. Maybe a silly question, but why have an INPUT *and* and OUTPUT rule? Isn’t the OUTPUT rule overkill? If somebody already can’t reach your server (packets are dropped), your server is not going to send any packets to them…, right?

    Reply Report comment

    1. Sander, I think it might be because some scanners will continue to try even if incoming traffic is dropped, should they get any traffic back at all from attempts to brute-force entry into a system. Mayhap? Prithee? Perchance? Bueller?

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  12. Improved for blocking ip ranges:

    BLOCKDB="/root/ip.blocked"
IPS=$(grep -Ev "^#" $BLOCKDB)
for i in $IPS
do
iptables -A INPUT -p tcp --destination-port 22 -m iprange --src-range $i -j DROP
#iptables -A OUTPUT -d $i -j DROP
done

    The /root/ip.blocked looks like:

    1.0.1.0-1.0.1.255
1.0.2.0-1.0.3.255
1.0.8.0-1.0.15.255
1.0.32.0-1.0.63.255
1.1.0.0-1.1.0.255
1.1.2.0-1.1.3.255
1.1.4.0-1.1.7.255
1.1.8.0-1.1.15.255
1.1.16.0-1.1.31.255
1.1.32.0-1.1.63.255
1.2.0.0-1.2.1.255
1.2.2.0-1.2.2.255
...
...
...

    I got it from http://ipblocklist.com

    This is our first day without login attempts from China. Cheers!

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  13. “or add following script line to existing iptables shell script:”
    how do I do that? I’m on ubuntu, iptables are in /sbin and appear encrypted…..

    any help appreciated as this looks to be a simple way to restrict a number of ip’s but I’m stuck! thanks.

    Reply Report comment

  16. Hello,

    I want to block USERS who access a particular IP, Example 192.27.5.115 (Which is a server IP) and i don’t want any users to access the IP. How can i restrict users to log into the particular IP? I dont have info about all User IP’s.

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