Re: Creating a routing program - the basics

["J." <mailing-lists@xs4all.nl>]

On Tue, 23 Oct 2007, Mateus Interciso wrote:

> On Tue, 23 Oct 2007 15:56:22 +0200, Steve Graegert wrote:
> 
> > On 10/23/07, Mateus Interciso <p.zarnick@gmail.com> wrote:
> >> On Tue, 23 Oct 2007 13:15:11 +0200, Steve Graegert wrote:
> >>
> >> > On 10/23/07, Mateus Interciso <p.zarnick@gmail.com> 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
> >> > -
> >> > To unsubscribe from this list: send the line "unsubscribe
> >> > linux-c-programming" in the body of a message to
> >> > majordomo@vger.kernel.org More majordomo info at
> >> > http://vger.kernel.org/majordomo-info.html
> >>
> >> Thank you, this will help.
> >> Do you have any book/site where I can take a deep look into how to do
> >> that stuff?
> > 
> > I can't make any recommendations beyond the well-known programming books
> > like Steven's UNP and O'Reilly's "Understanding the Linux Kernel". 
> > Additionally, you may find Sams Publishing 's "Linux(R) Socket
> > Programming" (0672319357) useful.
> > 
> > 	\Steve
> > 
> > --
> > 
> > Steve Grägert
> > DigitalEther.de
> > -
> > To unsubscribe from this list: send the line "unsubscribe
> > linux-c-programming" in the body of a message to
> > majordomo@vger.kernel.org More majordomo info at 
> > http://vger.kernel.org/majordomo-info.html
> 
> Thank you, I'll take a look at those books :D
> 
> Mateus

Hi,

I would most certainly in the first place go for the following books by Richard Stevens:

# TCP/IP Illustrated, Volume 1: The Protocols, Addison-Wesley, 1994.
# TCP/IP Illustrated, Volume 2: The Implementation, Addison-Wesley, 1995.
# TCP/IP Illustrated, Volume 3: TCP for Transactions, HTTP, NNTP, and the UNIX Domain Protocols, Addison-Wesley, 1996.
# UNIX Network Programming, Volume 1, Second Edition: Networking APIs: Sockets and XTI, Prentice Hall, 1998.
# UNIX Network Programming, Volume 2, Second Edition: Interprocess Communications, Prentice Hall, 1999.

for a complete list of Richard Steven's books:
http://www.kohala.com/start/#books
or amazon... 

Than the source-code of libpcap [tcpdump] is always very helpful.

Maybe also another suggestion;
Effective TCP/IP programming by Snader [addison wesley]

But the R.Stevens books are definitely the way to go if starting out with C topics like you've describe above.

GoodLuck.

J.

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