On Tue, 23 Oct 2007 13:15:11 +0200, Steve Graegert wrote:
> 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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Thank you, this will help.
Do you have any book/site where I can take a deep look into how to do
that stuff?
MAteus
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