Raw Socket promiscuous mode not sniffing what I write

Question

I am writing a program with a Raw Socket in promiscuous mode and I need the raw socket not sniff the packet I send. I need to read only the data over the ethernet rx wire (not the tx wire). It's posible?

Thanks a lot.

Answer 1

The solution is to look in the read packet if it is a PACKET_OUTGOING. Using this option you can diference the packet you put in the ethernet tx wire and the packet you read from the rx wire.

Open the Socket in promiscuous mode:

char* i = "eth0";
int fd;
struct ifreq ifr;
struct sockaddr_ll interfaceAddr;
struct packet_mreq mreq;

if ((fd = socket(PF_PACKET,SOCK_RAW,htons(ETH_P_ALL))) < 0)
    return -1;

memset(&interfaceAddr,0,sizeof(interfaceAddr));
memset(&ifr,0,sizeof(ifr));
memset(&mreq,0,sizeof(mreq));

memcpy(&ifr.ifr_name,i,IFNAMSIZ);
ioctl(fd,SIOCGIFINDEX,&ifr);

interfaceAddr.sll_ifindex = ifr.ifr_ifindex;
interfaceAddr.sll_family = AF_PACKET;

if (bind(fd, (struct sockaddr *)&interfaceAddr,sizeof(interfaceAddr)) < 0)
    return -2;


mreq.mr_ifindex = ifr.ifr_ifindex;
mreq.mr_type = PACKET_MR_PROMISC;
mreq.mr_alen = 6;

if (setsockopt(fd,SOL_PACKET,PACKET_ADD_MEMBERSHIP,
     (void*)&mreq,(socklen_t)sizeof(mreq)) < 0)
        return -3;
//...

And read. Now, We can differentiate between the Rx and Tx ethernet wire:

unsigned char buf[1500];
struct sockaddr_ll addr;
socklen_t addr_len = sizeof(addr);
n = recvfrom(fd, buf, 2000, 0, (struct sockaddr*)&addr, &addr_len);
if (n <= 0)
{
    //Error reading
}
else if (addr.sll_pkttype == PACKET_OUTGOING)
{
    //The read data are not writing by me.
    //Use only this data to copy in the other network.
}

And it's all. Using it I don't read the data I write. I avoid the loop when I copy the network 1 frames to network 2 and the network 2 frames to network 1.