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  1. #1

    iptables drop output on given interface

    I've got a desktop with two NICS eth0 & eth1. eth0 has an ip and is the in/out access to the desktop. eth1 has no ip, it is listening to traffic coming in from a cable modem. I want to use iptables to drop all output packets from this interface and allow output from eth1 but when I try:
    iptables -A OUTPUT -i eth1 -j DROP
    I get the error, "iptables v1.2.11: Can't use -i with OUTPUT"

    So, I figure that I could set the default output policy to DROP and then allow output from the ip given to eth0. Is this gonna work and is it a feasible solution?

  2. #2

    follow up

    Well, that didnt work. If I set OUTPUT default policy to drop than I can't set the loopback interface OUTPUT policy to accept and I get weird errors when restarting the desktop. Trying to set lo's output to accept gives me the same error as before.

    Any help?

  3. #3
    Linux Guru Lazydog's Avatar
    Join Date
    Jun 2004
    The Keystone State
    That should be

    iptables -A OUTPUT -o eth1 -j DROP
    Loopback can be setup as follows:

    iptables -A INTPUT -i lo -j ACCEPT
    iptables -A OUTPUT -o lo -j ACCEPT


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  5. #4



    didnt know about the -o, just looked it up in man iptables (something I should of done first I guess) and now it makes sense

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