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

Posted on in Categories Iptables, Linux, Security last updated June 26, 2005

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 202.54.1.22 from making any outgoing connection:
iptables -A OUTPUT -d 202.54.1.22 -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 192.168.1.2 only, enter:
iptables -A OUTPUT -p tcp -d 192.168.1.2 --dport 5050 -j DROP

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

For more information see iptables(8) 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)

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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30 comment

  1. 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 192.168.1.2 will be block/denied access to server/ip 192.168.1.10

    thanks

  2. 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.

  4. 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,
    k.

    1. 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:
      ESTABLISHED
      The packet is associated with a connection which has seen packets in both directions.
      RELATED
      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).

        1. 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).

  5. 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

  9. 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: 192.168.1.10 to 192.168.1.50) and toplevel peoples wants full internet access (Ex: 192.168.1.51 to 192.168.1.55) please need some help

    Note : Already blocked some sites for all (192.168.1.0/255.255.255.0) 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
    *nat
    :PREROUTING ACCEPT [21:3311]
    :POSTROUTING ACCEPT [1:241]
    :OUTPUT ACCEPT [1:241]
    -A POSTROUTING -o eth1 -j MASQUERADE
    COMMIT
    # Completed on Tue Dec 29 11:20:21 2009
    # Generated by iptables-save v1.3.5 on Tue Dec 29 11:20:21 2009
    *filter
    :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
    COMMIT
    # Completed on Tue Dec 29 11:20:21 2009

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

    a kind of trape…

  11. 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 ?

  13. sir,
    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.

  16. 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

  18. 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.

  19. Hi,

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

  20. Hi,
    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…..

  21. 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.

    Thanks

  22. Hi All,

    i want to block port 1202 & 22 for all the IP and only want to allow any specific Ip ex.1.2.3.4 in cent 5.9 64bit

    Please help me to shortcut it.

    Waiting for your reply.

  23. Hi Mohsin,

    Step 1 :

    iptables -I INPUT -p tcp --dport 1202,22 -s 1.2.3.4 -j ACCEPT

    Step 2:

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

    iptables save and restart

  24. Your company network comprises of a number of publically accessible servers located in a DMZ and a number of hosts and a File Server located in the Internal Office Network. How you would configure the two Linux Firewalls (LF1 and LF2) using iptables program to allow the external world (INTERNET) access the services located in the DMZ, but on the other side to protect the Internal Office Network from INTERNET threats?

  25. How you would configure the two Linux Firewalls (LF1 and LF2) using iptables program to allow the external world (INTERNET) access the services located in the DMZ, but on the other side to protect the Internal Office Network from INTERNET threats? The services located in the DMZ has mail server and HTTP server and on the office network there is a FTP server and 4 Computers. Thanks

  26. Hi
    I need to block the Internet access and LAN access to a computer with in the network using iptables.

    Could you please help me on this..

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