Question

I’m making a program which create a RAW socket in order to read all traffic. Between the call of socket() and recvfrom() (last one is in a loop to get out all packets from buffer) I wait 5s.

When I run the program, I send about 200 packets with hping3 command in « faster mode » (to fill in the buffer fastly) to my program. As soon as 5s are elapsed, my program extract about 150 packets from the buffer.

I try to change the size of the receive buffer to get better result:

int a = 65535;
if ( (setsockopt(sockfd, 0, SO_RCVBUF, &a ,sizeof(int)) ) < 0 )
{
    fprintf(stderr, "Error setting sock opts..\n");
}

However, whatever is the value of « a », 1 or 10000000, it seems nothing changes, I still get ~150 packets from the buffer.

What’s the problem?

Edit: Value of « a » is verified with a getsockopt call.

Answer 1

The level argument to setsockopt should be SOL_SOCKET, not 0:

int a = 65535;
if (setsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &a, sizeof(int)) == -1) {
    fprintf(stderr, "Error setting socket opts: %s\n", strerror(errno));
}