On 10/23/07, Mateus Interciso <p.zarnick@xxxxxxxxx> wrote:
> Hello, I'm currently on university, and for my graduation paper, I'll be
> implementing a routing algorythm, by hand, in C.
> The routing algorythm itself is not easy, but one of the starting parts
> of it, is to find a way of discovering the MAC that it is currently
> connected to, maybe is bether if I draw, since I'm not really that good
> in english:
>
> [PC with n NICs]-----(n cables)---->[n PCs]
>
> I have full control of the first PC, of course, since is the one I'm
> implementing the router, so I do know the MAC of it, but how to discover
> the MAC on the other end of the n lines, so I can start sending packets?
Probably this is a starting point: (not tested)
___ BEGIN SOURCE ___
#include <iostream>
#include <stdio.h>
#include <netdb.h>
#include <netinet/if_ether.h>
int read_mac(void) {
int sock, sockfd, n, cnt;
char buffer[2048];
unsigned char *iphead, *ethhead;
struct ether_addr ether;
if ((sock = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP))) < 0) {
perror("socket");
exit(1);
}
while (1) {
if ((n = recvfrom(sock, buffer, 2048, 0, NULL, NULL)) == -1) {
perror("recvfrom");
close(sock);
exit(1);
}
ethhead = (unsigned char *)buffer;
if (ethhead != NULL) {
iphead = (unsigned char *)(buffer + 14); // Skip Ethernet header
printf("Peer MAC: "
"%02x:%02x:%02x:%02x:%02x:%02x\n",
ethhead[0], ethhead[1], ethhead[2],
ethhead[3], ethhead[4], ethhead[5]);
printf("Source MAC: "
"%02x:%02x:%02x:%02x:%02x:%02x\n",
ethhead[6], ethhead[7], ethhead[8],
ethhead[9], ethhead[10], ethhead[11]);
if (*iphead == 0x45) { // Check for IPv4, no options present
printf("Peer IP: %d.%d.%d.%d\n",
iphead[12], iphead[13],
iphead[14], iphead[15]);
printf("Source IP: %d.%d.%d.%d\n",
iphead[16], iphead[17],
iphead[18], iphead[19]);
printf("Protocol (UDP = 11): %02x Hex\n", iphead[9]);
}
}
}
return 0;
}
int main(int argc, char **argv) {
read_mac();
return EXIT_SUCCESS;
}
___ END SOURCE ___
Honestly, you should make yourself acquainted with low-level network
programming. Otherwise you'll be asking a lot of theses questions in
the future. Anyway, hope this helps.
\Steve
--
Steve Grägert
DigitalEther.de
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