TUN/TAP hacking - Kernel

This is a discussion on TUN/TAP hacking - Kernel ; Hi, I need some advice from network stack experts, so I hope this is the right place to ask. I thought I'd be able to use the TAP interfaces to create some sort of a network emulator. For a start ...

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Thread: TUN/TAP hacking

  1. TUN/TAP hacking

    Hi,

    I need some advice from network stack experts, so I hope this is the right
    place to ask.

    I thought I'd be able to use the TAP interfaces to create some sort of a
    network emulator. For a start I just "bridged" two tap interfaces, much in
    the same way as the example of br_select.c from http://vtun.sf.net , assigned
    both interfaces different IPv4 addresses (both with a /32 prefix), set them up
    and tried to transmit a UDP packet from one address to the other through the
    bridge. Both logs from my bridge program and tcpdump tell me that the packets
    are flowing as expected, but somehow the destination process doesn't get the
    packets (despite all correct bind, etc).

    Is it simply that the stack inconditionally drops any packet with the same
    source (IP and/or MAC) address as some local interface?

    As ARP resolution seems not to work either (I had to put permanent entries in
    the neighbor table), I suppose this is the case indeed.

    Could anyone confirm that? (please CC me, I've not subscribed)

    Thanks,

    Ignacy

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  2. Re: TUN/TAP hacking

    Ignacy Gawedzki wrote:
    > I need some advice from network stack experts, so I hope this is the right
    > place to ask.


    The Linux kernel networking folks hang out at netdev
    (netdev@vger.kernel.org). I've CC'd them...

    > I thought I'd be able to use the TAP interfaces to create some sort of a
    > network emulator. For a start I just "bridged" two tap interfaces, much in
    > the same way as the example of br_select.c from http://vtun.sf.net , assigned
    > both interfaces different IPv4 addresses (both with a /32 prefix), set them up
    > and tried to transmit a UDP packet from one address to the other through the
    > bridge. Both logs from my bridge program and tcpdump tell me that the packets
    > are flowing as expected, but somehow the destination process doesn't get the
    > packets (despite all correct bind, etc).
    >
    > Is it simply that the stack inconditionally drops any packet with the same
    > source (IP and/or MAC) address as some local interface?
    >
    > As ARP resolution seems not to work either (I had to put permanent entries in
    > the neighbor table), I suppose this is the case indeed.
    >
    > Could anyone confirm that? (please CC me, I've not subscribed)
    >
    > Thanks,
    >
    > Ignacy
    >



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