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    SubjectRe: netfilter query
    On Sun, 21 Nov 2004, cranium2003 wrote:

    > Also,which headers are added when packet
    > reaches to netfilter hook NF_IP_LOCAL_OUT? I found
    > TCP/UDP/ICMP ,IP. Is that correct?


    netfilter is running at the IP layer and only reliably have access to IP
    headers and up. Lower level headers such as Ethernet MAC header is
    transport dependent and not always available, and certainly not available
    in NF_IP_LOCAL_OUT as it is not yet known the packet will be sent to an

    In some netfilter hooks it is possible to rewind back to the Ethernet MAC
    header but one must be careful to verify that it really is an Ethernet
    packet one is looking at when doing this. Unfortunately there is no
    perfect solution how to detect this.. For an example of how one may try to
    look at the Ethernet MAC header see ipt_mac.c. But be warned that it is
    possible for non-Ethernet frames to pass the simple checks done there..

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