Re: UDP problem revisited.
TomChapman wrote:
I have more related to this topic.
On the internet I have found some example code (see below) that uses
SOCK_RAW type and then uses recvfrom to get data. In the return data is
the MAC address.
Does SOCK_RAW work with CAsyncSocket?
Is this a way for me to learn the MAC addresses of the received data so
that I can distinguish between the sources of the data.
To get this to work will I have to abandon CAsyncSocket? What are the
disadvantages of doing this? Is this something I can do?
---------------------------------------------------------------------
#include <iostream>
#include <stdio.h>
#include <netdb.h>
#include <netinet/if_ether.h>
int _get_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("\n--------------------------------------"
"\nMAC destino (server): "
"%02x:%02x:%02x:%02x:%02x:%02x\n",
ethhead[0],ethhead[1],ethhead[2],
ethhead[3],ethhead[4],ethhead[5]);
printf("MAC origen (CAL30x): "
"%02x:%02x:%02x:%02x:%02x:%02x\n",
ethhead[6],ethhead[7],ethhead[8],
ethhead[9],ethhead[10],ethhead[11]);
if (*iphead==0x45) { // Double check for IPv4 and no options present
printf("IP destino (server): %d.%d.%d.%d\n",
iphead[12],iphead[13],
iphead[14],iphead[15]);
printf("IP origen (CAL30x): %d.%d.%d.%d\n",
iphead[16],iphead[17],
iphead[18],iphead[19]);
printf("Protocolo (UDP=11): %02x Hex\n",iphead[9]);
}
}
}
return 0;
}
int main(int argc, char **argv)
{
_get_MAC();
return 0;
}
Many months ago people on this newsgroup helped me with a UDP network
problem. I now have some additional information.
To recap... My program runs on a server and receives UDP packets
generated on another computer by a program from another manufacture. The
third party program is part of a system of several computers and
software developed by the 3rd party. That network system is normally a
closed system. Which means there is one network switch that each of the
3rd party computers connects to AND THERE IS NO CONNECTION TO ANY
OUTSIDE COMPUTER OR THE INTERNET. They just talk to each other.
In my case I connect to this switch and therefore I can see the UDP
packets generated on this system. MY PROGRAM WORKS WELL.
Let me describe the problem...
I need to simultaneously connect my computer to three separate of these
3rd party systems and receive UDP data from all three. My plan was to
was to install multiple NIC cards in my server and connect one NIC to
each of the 3rd party systems.
The problem is that each 3rd party system uses identical IP addresses.
That is OK for the 3rd party system because the 3rd party systems
normally don't talk to each other. But the problem is that if I open a
UDP client connection I will receive data from all three systems, but I
won't be able to tell which system sent me an individual packet. I need
to know that info.
I CAN'T CHANGE THE 3RD PARTY PROGRAM, I can't change the IPs, I can't
change from UDP to TCP.
I have tried putting a Cisco router between one of the systems and my
server and having the router map the IP (translate) to something else.
In theory this works, but it doesn't because the packets go through an
additional router and they have a UDP drop count set so low that the
router drops the packet before it gets to me. There seems to be nothing
Cisco can do about that.
I guy who works for me is using WireShark and looking at the data. He
has noticed that every packet has the source IP and the source MAC
address. The IPs are the same on each system, but the MAC addresses are
not.
QUESTION: Is there some way for my software to see the MAC addresses of
the UDP packets, because I could use that to distinguish where the
packets cam from.
QUESTION: Is there some kind of middleware that I could use on my server
that would be able to view the MAC addresses and and somehow change the
IP addresses in the packets based on the MAC addresses? This would be
done so my program could recognize where each packet originated from.