How Do I Block an IP Address on My Linux server?

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How do I block an IP address or subnet under Linux operating system?

In order to block an IP on your Linux server you need to use iptables tools (administration tool for IPv4 packet filtering and NAT) and netfilter firewall. First you need to log into shell as root user. To block an IP address you need to type the iptables command as follows:


Syntax to block an IP address under Linux

iptables -A INPUT -s IP-ADDRESS -j DROP

Replace IP-ADDRESS with your actual IP address. For example, if you wish to block an ip address for whatever reason then type the command as follows:
# iptables -A INPUT -s -j DROP
If you have IP tables firewall script, add the above rule to your script.

If you just want to block access to one port from an ip to port 25 then type command:
# iptables -A INPUT -s -p tcp --destination-port 25 -j DROP
The above rule will drop all packets coming from IP to port mail server port 25.

CentOS / RHEL / Fedora Block An IP And Save It To Config File

Type the following two command:
# iptables -A INPUT -s -j DROP
# service iptables save

How Do I Unblock An IP Address?

Use the following syntax (the -d options deletes the rule from table):
# iptables -D INPUT -s -j DROP
# iptables -D INPUT -s -j DROP
# service iptables save

See also:

  1. You can write a shell script to block lots of IP address and subnets.
  2. Iptables: Unblock / Delete an IP Address Listed in IPtables Tables

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin, DevOps engineer, and a trainer for the Linux operating system/Unix shell scripting. Get the latest tutorials on SysAdmin, Linux/Unix and open source topics via RSS/XML feed or weekly email newsletter.


50 comment

  1. hi dear,

    h a u?

    i have aproblem to ristrick the wab page on client side.

    i have linux server to run internt. i make gateway on that server and use it on other system to run internet.

    her i want to on clint system only my specify wab pages is open.

    plz u can help me how i confuger it.

    my network is on workgroup


  2. Ther are two solution:

    1) the best practice you use a proxy server like suqid in the gateway machine. Then define ACL on the squid.
    say you want to deny access to and
    acl all src
    acl web_yahoo dest
    acl web_rediff dest

    http_access deny web_yahoo all
    http_access deny web_rediff all

    2) this option is throhgh iptables, assume that your gateway acts as a firewall.

    iptables -A INPUT -p tcp –destination-port 80 -d -j DROP

    it will drop any request to port 80 of yahoo from any source.

  3. Please send me the code in Linux c to block the website typed on the browser. or send the references where i can get

  4. Hi I added:

    iptables -A INPUT -s -j DROP

    and kept checking my apache logs, after a short pause of no requests from

    it resumed ?? Could this mean I have been hacked ?

    EG: - - [21/Jun/2008:17:10:40 +1000] "GET /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////photogallery.php?album_id=1 HTTP/1.1" 200

  5. You need to add iptables -A INPUT -s -j DROP to your firewall script. Once added cannot connect to your apache. Do you run any special firewall script such as apf?

  6. hi,
    i need an iptable rule for a website( not to go through squid(proxy).could you pls send me the iptable rule for this one?


  7. joel, i think you do it without iptables rule using squid configuration and I don’t think its possible to have such a rule. What do you say vivek ?

  8. Yes, nilesh is right. It all depends upon your setup. Do you have squid proxy installed? If so there is an option to skip from squid cache using ACL. Iptables is for filtering and restricting traffic.

  9. @vivek and S. Nilesh,

    yes i have a squid transparent proxy caching server and firewall in the same box.could you kindly post here the acl rules to bypass webmd from going through squid. btw im using the old 2.5 stable 6 version.thank you very much to both of you for responding to my question.


  10. @ S.Nilesh and Vivek,

    hi again,

    i thought i should ask this question. how would you allow https traffic for one particular site on the network but restrict all other https traffic with an iptable rule.i have users bypassing my proxy redirector(squidguard) using https and i cannot block port 443 on my firewall because it is being used by a remote GUI application which is also being used by my users.

  11. lol dont use -A

    im not an iptables guru, but ive fought off plenty of attacks, and hack attempts, heres how chain worx k,
    # Drop
    rule 1
    rule 2
    rule 3
    end of chain default rule (drop all or accept all however)
    rule4 your new rule

    so if you use the -A which is the add option its going to add to the drop chain right,
    which will put it after an absolute depending on who or how your iptables is setup.
    after an absolute is parsed, by iptables it wont read any further into the chain, there for your add option will never work as good as the insert flag -I

    # drop

    rule4 – our new rule here
    drop all

    make sense?

  12. Hi all,

    Are these IP table entries are permanent? Recently I had blocked an IP using the step mentioned above. ( i.e. iptables -A INPUT -s -j DROP ) I wanted to know, if my server reboots, does that entry can withstand the reboot or will loose upon reboot?

    1. iptables -I INPUT -s ! {IP ADDRESS} -j DROP

      The Bang character (!) basically means NOT, so the line above would say drop ALL packets NOT going to ip address

  13. why it’s working only if I use it like that? (not iptables -A INPUT -s -j DROP)
    iptables -I INPUT -s -j DROP

  14. Hi !!
    I have RHEL5 installed and i have tried the command #iptables -A INPUT -s -j DROP. i hv logged into root and opened terminal…..and then typed this… bt it didn’t work!! Plz tell me the actual way to run this command… i really need this very urgently…

  15. Hi !!
    I have RHEL5 installed and i have tried the command #iptables -A INPUT -s IP ADDRESS -j DROP. i hv logged into root and opened terminal…..and then typed this… bt it didn’t work!! Plz tell me the actual way to run this command… i really need this very urgently…

  16. Do anyone know how to block IP like that >
    202.56.***.*** that means under 202.56. all IP will be blocked.


    1. Use a mask – so to block, say, 202.101.*.* you would specify the address in CIDR format as

      Plenty of CIDR calculators on Google if you need help or just remember ranges as : = to = to = to

  17. I am having some problems leaving a remark. I’ve attempted refreshing several times as well as closing and opening opera. Is anyone else having a problem on this article?

  18. Hi Vivek
    This site is very useful and provides “to the point” information. Keep up the good work.

    Unix aficionado

  19. I tested this and blocked the ip from my phone through ip tables. It didn’t block anything i could still ssh in i could still browse the website I host on this server and connect via ftp so I went into my iptables file
    and typed this
    -A PREROUTING -s PhoneIPAddress -j DROP
    saved closed
    service restart iptables
    and then my phone had no access what so ever. Is this just a different way or am I going to run into problems by blocking ip addresses at the PREROUTING level

  20. hi
    i am new with IP tables stuff and i have a problem….
    i have a pc Contain a fedora OS and i want to make a small network (4 PCs Contain XP OS) and using the pc of fedora OS as a firewall
    i want to Prevent the ping (i think it called(ICMP)) in the privat network and prevent one of the PCs from Browsing internet(prevent port 80 and 81 as i think)
    and i still don’t know how to make the internet go Through the firewall to the private network…

    note: WAN = eth0
    LAN = eth1
    any one can help plz!!!!

  21. How can I block connections ONLY TO port 80 of a range of addresses?

    I do not want to create 300 single rules for.port 80. Port constraint required as must allow traffic to port 443

  22. Not blocking any of the addresses in the range:

    iptables -A INPUT -s -p tcp –destination-port 80 -j DROP

    iptables 1.4.10 (android)


  23. If you have other rules in your INPUT chain you do need to use the -I option to insert your block at the top of the chain.

    iptables -I INPUT -s -j DROP

    to block ip-adres

  24. hi there,
    i have an error called 705 (failure to connect web server) when i upload the website on the server .
    it bocks my ip because all other net connection open it so plz give me the better solution for that.

  25. it working fine.
    i am able to block ip address and unblock it. fine working.

    but how to block a user ??

    as a user using same mobile and changing ip-address and able to access server.

  26. Another way to do this is to use routing table: use a black hole route to preventing your machine from sending anything back will prevent most attacks:

    ip route add dev lo


    ip route add dev lo # block ssh hacking host

    This will block any packets from going back to and break any TCP connections. This will not prevent a SYN flood DoS though.

  27. I have roughly 5,000 lines in my iptables blocking all of China (at least those not using a proxy or remote). Can anyone think of any performance degradation that may be had from having so many lines in the iptables?

  28. What if the IP isn’t blocked by iptables ? I use the same rules and my website keeps getting hundreds of thousands of pw bruteforce attempts and the iptables counter of that rule stays at zero.

  29. Thanks for the advice. I have a very pesky chinese ip doing a brute-force or DOS attack on my machine. Now – nothing. Thanks again.

  30. Im using this simple heavy duty bash script as root for some like 15 minutes and more of 30MB IP’s are blocked:

    curl -s 
    | grep -A 2 Bluetack 
    | sed -n s/.*value=(http:.*).*/1/p 
    | xargs wget -O  
    | gunzip 
    | egrep -v ^# > blacklist
    grep -Eo [0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3} blacklist > blacklist-ip
    grep -Eo [0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}[-][0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3} blacklist > blacklist-ip-range
    sed -i -E s/[-][0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}./// blacklist-ip-range
    sort blacklist-ip | uniq -u > blacklist-ip-sorted
    sort blacklist-ip-range | uniq -u > blacklist-ip-range-sorted
    while read IPADDR
    route add $IPADDR gw lo &
    done < blacklist-ip-range-sorted
    while read IPADDR
    route add $IPADDR gw lo &
    done < blacklist-ip-sorted
    rm blacklist-ip
    rm blacklist-ip-sorted
    rm blacklist-ip-range
    rm blacklist-ip-range-sorted
  31. I get these brute force attacks a lot
    IPTables isn’t enough to stop them and neither is hosts.deny
    I blackhole the buggers by router them to
    That way their scripts hang and hang waiting for a response, but they never get one heh heh
    Example I block a specific IP:
    route add gw lo

    Or I block the entire subnet (Mostly China)
    route add -net gw lo

    I do this from Linux command line as root.
    In case you want to test it using your cell phone IP or something this is how you remove it
    route delete IPADDRESS

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