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  1. #1

    Forwarding ICMP packets with NAT

    Hi there,
    I was hoping to set a linux box up by my router to respond to incoming ICMP packets for a series of WAN delay reading I need, however I'm very confused about exactly how ICMP is handled.
    Without using a port I can't configure any port based forwarding, but I have an idea that it might be handled by NAT, is this the case?
    Has anyone done this before? The router is a thompson using a propriety unix like kernel from what i can tell.
    Any help would be appreciated.
    Many thanks
    Neil r w

  2. #2
    Super Moderator Roxoff's Avatar
    Join Date
    Aug 2005
    Nottingham, England
    I believe that ICMP is protocol at the same level as TCP/IP, but NAT works with the IP layer, so ICMP cannot be routed using it.

    I have no idea if similar forwarding mechanisms exist for ICMP, sorry.
    Linux user #126863 - see

  3. #3
    Linux Guru Lazydog's Avatar
    Join Date
    Jun 2004
    The Keystone State
    While I have not tried it I do not see any reason why you could not DNAT ICMP traffic to another IP Address. ICMP is a protocol and like any other protocol you should be able to DNAT it.

    you could try something like this;

    iptables -t nat -A PREROUTING -p icmp --icmp-type 0 -j DNAT --to-destination
    You will have to adjust to your needs. Give it a shot and let us know how you make out.

    Here is a list of different types of ICMP


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    Linux User #296285
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