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    SubjectRe: Packet capturing, iptables and eth0 vs. dummy0
    That's because when you try locally, you end up using lo0, not eth0.


    On Wed, 17 Nov 2004 21:30:33 +0100, DervishD <lkml@dervishd.net> wrote:
    > Hi all :)
    >
    > I've noticed that, no matter what filtering is iptables doing,
    > tcpdump gets all packets from interface eth0 as seen in the bus, but
    > doesn't do the same in dummy0. I'll explain it further...
    >
    > Let's say that I'm filtering all incoming TCP SYN packets on all
    > interfaces that have a destination port of 6666 (for example), and
    > I'm listening, with tcpdump, to all packets in eth0. Well, I use
    > another computer to try to connect to port 6666 of the machine
    > running tcpdump and the packet filter, and obviously I'm unable to
    > connect (without the filter I can do it normally), but I see the SYN
    > packets in the output of tcpdump.
    >
    > If I do exactly the same from the machine running tcpdump and the
    > filter, I cannot connect (without the filter I can), but no output
    > comes from tcpdump, which is exactly what I expected in the case
    > explained in the paragraph above.
    >
    > Is is normal? Is normal that tcpdump shows packets before they
    > enter the filter when the interface is a real one (eth0) but no when
    > you access through a dummy interface or localhost, or am I missing
    > anything?
    >
    > Thanks a lot in advance :)
    >
    > Raúl Núñez de Arenas Coronado
    >
    > --
    > Linux Registered User 88736
    > http://www.dervishd.net & http://www.pleyades.net/
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    Don Lafontaine
    http://www.avsim.com/hangar/utils/freefd
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