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Date: Fri, 20 May 2005 20:16:25 -0700 (PDT)
From: Daniel Valencia <fetrovsky@yahoo.com>
To: freebsd-net@freebsd.org
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Subject: Re: sending MAC packets --- again, and again
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Hello all,

I know this may sound funny, but I'm still wrestling
with libpcap because I send packets and I cannot read
them.  I tried also some example code of a toy sniffer
from a tutorial to pcap, and it behaves just like my
code.  As my code is pretty compact, I'm posting it
here.


I'm sending from another machine (i'm using a hub this
time) an Ethernet message with the payload " la lara
la la la la " using broadcast to/from addresses. 
tcpdump in the sniffing machine tells me that the
message is in the wire, but my sniffer just stalls and
eventually will report a totally unrelated message.

Same thing happens with the other pcap example I
borrowed.  Sending machine is 4.11-RELEASE, listening
machine is 5.4-RELEASE.

Any help will be grately appreciated!

Thanks

- Daniel



#include <iostream>
#include <pcap.h>

void printhexdigit( int val, int pos )
{
        int dig = (val & (0xf << pos)) >> pos;
        std::cout << (dig>9)? 'a'+dig-0xa: '0'+dig;
}

int main()
{
        pcap_t *handle;
        pcap_pkthdr header;
        char errbuf[PCAP_ERRBUF_SIZE];
        errbuf[0] = 0;

        handle = pcap_open_live( "xl0", BUFSIZ, 1, 0,
errbuf );

        if( errbuf[0] )
                std::cout << errbuf << std::endl;

        const u_char *q = pcap_next( handle, &header
);

        std::cout << "sniffed a packet of length " <<
header.len << std::endl;

        for( int i = 0; i < header.len; i++ )
        {
                std::cout << ((i % 0x10)? ((i % 8)? "
": " - "): "\n");
                printhexdigit( q[i], 1 );      
printhexdigit( q[i], 0 );
        }

        std::cout << std::endl;

        return 0;
}


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