Linux Iptables Block Outgoing Access To Selected or Specific IP Address / Port

by on June 26, 2005 · 27 comments· LAST UPDATED October 18, 2013

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You would like to block outgoing access to particular remote host/ip or port for all or selected service/port. In this quick tutorial I will explain how to use iptables to block outgoing access.

Block Access To Outgoing IP Address

The following rule will block ip address from making any outgoing connection:
iptables -A OUTPUT -d -j DROP

The above will block chat server ip address or site having dangerous contains such as viruses or malware.

Block Access To Outgoing IP TCP / UDP Port Number

To block specific port number such tcp port # 5050, enter:
iptables -A OUTPUT -p tcp --dport 5050 -j DROP

To block tcp port # 5050 for an IP address only, enter:
iptables -A OUTPUT -p tcp -d --dport 5050 -j DROP

Finally, you need to save your firewall rules. Under CentOS / RHEL / Fedora Linux, enter:
# /sbin/service iptables save
# /etc/init.d/iptables save

For more information see Linux iptables(8) man page or our Linux firewall tutorials from the following resources:

  1. CentOS / Redhat Iptables Firewall Configuration Tutorial
  2. Linux Configure Firewall Using Shorewall Under RHEL / CentOS
  3. Debian / Ubuntu Linux: Install and Configure Shoreline Firewall (Shorewall)
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{ 27 comments… read them below or add one }

1 thon August 8, 2007 at 10:15 am

IPTABLES. I just want to know how to block a certain IP address or network to access a specific server. lets say the host/ip will be block/denied access to server/ip



2 Jes October 17, 2007 at 2:35 am

Not one freaking person on the whole internet has an example of how to use iptables to stop one single machine from being able to access one single IP address.


3 Sayajin January 29, 2014 at 12:56 pm

iptables -A INPUT -s -d -j DROP


4 nixCraft October 17, 2007 at 5:39 am


Drop single system

iptables -A INPUT -d -j DROP

Try following urls for more …
How do I Drop or block attackers IP with null routes?
Linux Iptables block incoming access to selected or specific ip address



5 k December 10, 2007 at 6:50 pm

Hi, Can anyone help?
How do I block the outgoing traffic from x IP address to y IP address, but allow the incoming traffic from y to x? For some reason when I accept input and then do output drop it doesn’t allow inputs. Additionally, I did:
/sbin/iptables -A INPUT -p icmp –icmp-type echo-reply -j ACCEPT
/sbin/iptables -A INPUT -p icmp –icmp-type echo-request -j ACCEPT
But can’t ping x from y and vice versa. Please help.
Thank you,


6 Cody July 26, 2014 at 12:07 pm

This is old but whatever, for those who don’t know:

For dropping OUTPUT and accepting certain connections (by port or whatever):
You need to use either state module (or preferably nowadays, conntrack with ctstate) to allow ESTABLISHED,RELATED
And yes this applies to non tcp because:
The packet is associated with a connection which has seen packets in both directions.
The packet is starting a new connection, but is associated with an existing connection, such as an FTP data transfer, or an ICMP error.

For ping, you’ll need to allow OUTPUT icmp traffic if you’re setting the policy to DROP. That is: the proper icmp types. You’re better of rate limiting though (fragmented packets are generally nowadays an indication of malicious activity but that’s another story entirely).
You should also allow ESTABLISHED,RELATED for INPUT as well (think about what I pasted above, as to why that is: if you don’t then a connection-oriented protocol e.g., one that uses TCP, will have issues.. keep in mind it might not be that someone is connecting to your server but YOUR server initiates the connection = output and then the remote host responds but if you don’t allow related then you’ll run in to trouble. Keep in mind outgoing connection requests and how/what they do, ports included as well as what type of connection, when you’re thinking about this).


7 Curl February 15, 2015 at 8:42 pm

Your answer came a long time after but, hey, thanks! It gave me some enlightment.


8 Cody March 1, 2015 at 3:05 am

Welcome! Hope it answered your question(s) (or if it wasn’t you – since different name – I hope that it was helpful or useful in any case).


9 Prince September 9, 2008 at 9:36 am

Hi guys, Need help!!!!
Running red Hat Linux 7.1 2.96-98 and need to block a group of users using usernem from accessing internet. Limit the same users to have access between 1300 – 1400 hrs and 1600 – 1700 hrs. I’m using Linux as the proxy server. i’ve tried iptables -A OUTPUT -p TCP -m owner –uid-owner prince -j DROP, but this owner and –uid-owner are not recognised
Thank you


10 nixCraft September 9, 2008 at 10:53 am

You need to get Latest version RHEL 5.x or CentOS 5.x. Your distro is outdated and no longer supported.


11 Jose October 29, 2008 at 9:08 pm

Good article, very useful for me
Tks a lot


12 vinni November 17, 2008 at 4:47 pm

Thanks for the info dear .. Put some more info regd the bandwidth management


13 Murali December 30, 2009 at 1:48 pm

Hi Friends,

Iam using Fedora6.0 with squid server but clients accessing internet and mails in below iptable coniguration now i want to block internet for particular ip’s range (Ex: to and toplevel peoples wants full internet access (Ex: to please need some help

Note : Already blocked some sites for all ( but 5 people wants full access how to configure my iptables pls helpme

****************PRESENT IPTABLE CONFIGURATION***********************

# Generated by iptables-save v1.3.5 on Tue Dec 29 11:20:21 2009
# Completed on Tue Dec 29 11:20:21 2009
# Generated by iptables-save v1.3.5 on Tue Dec 29 11:20:21 2009
:INPUT ACCEPT [3822:1594474]
:FORWARD ACCEPT [115:7616]
:OUTPUT ACCEPT [2702:1165159]
-A FORWARD -i eth1 -o eth0 -m state –state RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -i eth0 -o eth1 -j ACCEPT
# Completed on Tue Dec 29 11:20:21 2009


14 Nerigal May 12, 2010 at 1:53 pm

is it possible to blacklist (ban from all) a source IP that would it a specific port of your choice ?

a kind of trape…


15 rakesh July 14, 2010 at 9:27 am

hi, i am newbie in linux, I am using Fedora 6.0 with squid server
i want to block gmail to specific subnet , how can i do it ?


16 sen3ca April 13, 2011 at 8:29 pm

nice, concise, and exactly what I was looking for. Thanks


17 imrankhan April 26, 2011 at 5:43 am

I am using Fedora 13 iptables i was blocking some websites. but selected user i have access perticuler websites.
plz find the some other commands.


18 rana May 10, 2011 at 9:41 am

I want to block a website from my linux server using iptables command for a local computer


19 Avin October 5, 2011 at 4:26 am

How to block Gmail using iptables ? I am using CentOS 5.7.


20 Dean Kamali April 19, 2012 at 4:28 pm

There should be –dport not -dport otherwise you will get

iptables v1.3.5: multiple -d flags not allowed
Try `iptables -h’ or ‘iptables –help’ for more information.

the correct syntax is
iptables -A OUTPUT -p tcp –dport 5050 -j DROP


21 Helpful Guy March 6, 2013 at 9:18 am

There should be ‘–dport’ not ‘-dport’ (double dash).


22 Ahmad June 23, 2013 at 1:14 am

Dean Kamali, thank you very much. I spent a long time trying to figure out what was wrong until I saw your comment.

To clarify, dport has to have two dashes before it.


23 Aravindan August 27, 2013 at 12:38 pm


Your Tuts are simply superb.
Please let me know the difference between using DROP and REJECT options .


24 vikas September 20, 2013 at 5:00 pm

Can anyone suggest me for blocking the internet access through fedora DHCP only allowing intranet access.some user also access the internet through USB dongle while at the same time they connect to the intranet i want to block there internet access when they are in network..It is a small enterprise network currently running on windows 2008 server and using the fedora for DHCP and FTP services…pls help…..


25 Muhammad Faisal Jamil February 12, 2014 at 9:03 am

hi guys, i want to allow one service which is published on live ip address with specific port like x.x.x.x:5768 through squid.
currently i am using RHEL 6.x and only specific sites are allowed through url_regix rule. so how can i implement this acl to allow only one web service on specific port.



26 Mohsin khan March 17, 2014 at 4:15 pm

Hi All,

i want to block port 1202 & 22 for all the IP and only want to allow any specific Ip ex. in cent 5.9 64bit

Please help me to shortcut it.

Waiting for your reply.


27 Aravindan R March 18, 2014 at 9:44 am

Hi Mohsin,

Step 1 :

iptables -I INPUT -p tcp --dport 1202,22 -s -j ACCEPT

Step 2:

iptables -A INPUT -p tcp --dport 1202,22 -j REJECT

iptables save and restart


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