Linux Iptables allow or block ICMP ping request

Posted on in Categories Debian Linux, Gentoo Linux, Iptables, RedHat/Fedora Linux, Security, Suse Linux, Ubuntu Linux last updated June 28, 2005

The Internet Control Message Protocol (ICMP) has many messages that are identified by a “type” field. You need to use 0 and 8 ICMP code types.

=> Zero (0) is for echo-reply

=> Eight (8) is for echo-request.

To enable ICMP ping incoming client request use following iptables rule (you need to add following rules to script).

My default firewall policy is blocking everything.

Task: Enable or allow ICMP ping incoming client request

Rule to enable ICMP ping incoming client request ( assuming that default iptables policy is to drop all INPUT and OUTPUT packets)

SERVER_IP="202.54.10.20"
iptables -A INPUT -p icmp --icmp-type 8 -s 0/0 -d $SERVER_IP -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT

iptables -A OUTPUT -p icmp --icmp-type 0 -s $SERVER_IP -d 0/0 -m state --state ESTABLISHED,RELATED -j ACCEPT

Task: Allow or enable outgoing ping request

To enable ICMP ping outgoing request use following iptables rule:

SERVER_IP="202.54.10.20"
iptables -A OUTPUT -p icmp --icmp-type 8 -s $SERVER_IP -d 0/0 -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT

iptables -A INPUT -p icmp --icmp-type 0 -s 0/0 -d $SERVER_IP -m state --state ESTABLISHED,RELATED -j ACCEPT

How do I disable outgoing ICMP request?

Use the following rules:

iptables -A OUTPUT -p icmp --icmp-type echo-request -j DROP

OR

iptables -A OUTPUT -p icmp --icmp-type 8 -j DROP

ICMP echo-request type will be block by above rule.

See ICMP TYPE NUMBERS (type fields). You can also get list of ICMP types, just type following command at shell prompt:
# /sbin/iptables -p icmp -h

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+.

25 comment

  1. This seems to be incomplete. An ICMP ping is an “icmp echo request” that is followed up by an “icmp echo reply”. So you need to specify the appropriate “–icmp-type” in your incoming and outgoing chains.

    Possible values for –icmp-type are listed by “iptables -p icmp -h”. There are a icmp packets you dont want to recieve or reply to.

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  2. >This seems to be incomplete
    Noop, this is not incomplete.

    >Possible values for –icmp-type are listed by “iptables -p icmp -h”. There are a icmp packets you dont want to recieve or reply to.

    Yup, but you don’t have to use them. I just prefer to keep it simple aka KISS. My Default firewall policy is block everything, so this works w/o problem.

  3. I beg to differ. IT is incomplete. You block everything, then you open all ICMP traffic. How does this block other types of ICMP traffic?

  4. iptables -A INPUT -p icmp –icmp-type 8 -s 0/0 -d $SERVER_IP -m state –state NEW,ESTABLISHED,RELATED -j ACCEPT

    Error: Bad argument `state’

  5. Nice…how about i can ping anyone but none cant ping me?…i mad lil rule

    iptables -A OUTPUT -p icmp –icmp-type echo-reply -s 192.168.1.50 -d 192.168.1.0/24 -j REJECT

    this for an single subnet πŸ™‚

  6. hi.. im from a networking background… couldnt play around that much at home coz of ChISCO too $$$$… i heard linux also can work as a router with their IPtables stuff… may i know:
    1. SERVER_IP=”202.54.10.20″ is whos address? me as a server or the client’s IP?
    2. 0/0 ?
    3. NEW,ESTABLISHED,RELATED (try to understand this on9, maybe yall have a clearer explanation)
    4. -m?

  7. How can I accept ICMP with a specific packetsize? I want to be able to ping my server from my windows notebook, but with -l 666 (for example), for monitoring purposes. But IPTABLES doesn’t seem to have an option to accept or denay a specific ping size. Is that correct?. Thanks in advance.

  8. This may be a dumb question, but I can’t find the answer anywhere else. After I make a rule change, do I have to reload iptables or stop/start to activate the change?

    1. Yes, you need to restart firewall if you made changes to config file.

      Reload script if you made changes to a shell script that loads all other rules.

  9. hi,
    i want to do ip spoofing for my excersize but i can’t !!!
    the question is :
    use iptables to modify your IP address to 10.2.3.4 when sending out icmp requests.

  10. Sigh. I _really_ wish administrators would STOP recommending (and actually following it) to block ICMP itself outright. Rate limit by all means, that’s good. Block fragmented packets (nowadays it is generally malicious). But blocking ICMP itself is a bad idea. And in IPv6 it is especially bad if you want a working connection, anyway (or I seem to remember.. it is vague at this time but there are certain differences for sure, in IPv6 that are absolutely necessary to be aware of if you don’t want to run in to problems). What ICMP stands for gives the reason (or should): internet control message protocol. It is for error reporting. You should block certain ICMP types, sure, but ping is a bad example of what to block (unless we’re talking spoofed packets or to broadcast (which by the way, 255.255.255.255 – that is, someone sending to such – will not send to every IP that exists… as an aside) or … but that’s different). Not heeding this advice only leads to network troubleshooting issues. And I’ll point something else out: blocking ping does nothing for security. Notthing (again, rate limiting is fine). Not a damned thing. It is a false sense of security. There’s other ways to find out if your system is there and blocking ping is hardly going to stop a would be attacker.

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