Protocol not available writing to eth?

[Sanders, Maarten (M.J.L.)]

Hi,

We are trying to convince a MOXA UC-7110 to act as a very simple
firewall. We want it to listen to UDP on eth0 and to forward the data to
eth1. At a later stage we apply our own filtering.

The code below compiles cleanly but returns:
"Protocol not available"
as soon as eth1 is opened.

Has anyone done a similar thing before or has some pointers to an
example? Most examples we find are not so 'raw' on the devices as we
intend.

Thanks,

Maarten Sanders


<<<<<tcpc1.c>>>>>>>


#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h> /* inet_ntoa() */

#include <sys/ioctl.h>

#include <linux/if.h>
#include <linux/if_ether.h>
#include <linux/ip.h>

#include <string.h>
#include <unistd.h>

#define BUFSIZE 2048

int main(void)
{
int i = 20;
int sock_r, sock_s;
ssize_t n;
unsigned char buffer[BUFSIZE];
char on = 1;
struct ifreq req, req_s;

    if ((sock_r = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP))) < 0)
    {
        perror("socket() error");
        return -1;
    }

/* bind device to the socket */
    strncpy(req.ifr_name, "eth0", sizeof(req.ifr_name));
    if (ioctl(sock_r, SIOCGIFFLAGS, &req) < 0)
    {
        perror("ioctl() error");
        return -1;
    }

/* set the interface promiscous mode */
    req.ifr_flags |= IFF_PROMISC;
    if (ioctl(sock_r, SIOCSIFFLAGS, &req) < 0)
    {
        perror("ioctl() error");
        return -1;
    }
// en zend

    if ((sock_s = socket(PF_PACKET, SOCK_RAW, htons(IPPROTO_RAW))) < 0)
    {
        perror("socket()s error");
        return -1;
    }

/* bind device to the socket */
    strncpy(req_s.ifr_name, "eth1", sizeof(req_s.ifr_name));
    if ( ioctl(sock_s, SIOCGIFFLAGS, &req_s) < 0)
    {
        perror("ioctl()s error");
        return -1;
    }


    if (setsockopt(sock_s,IPPROTO_RAW,IP_HDRINCL,&on,sizeof(on)) < 0 )
//ioctl(sock_s, SIOCSIFFLAGS, &req_s) < 0)
    {
        perror("ioctl()s error");
        return -1;
    }

    printf("Initialized ! %d %d\n",sock_r ,sock_s);
    sleep(3);

    while (1)
    {
        if ( (n = read(sock_r, buffer, BUFSIZE)) <= 0 )
        {
            printf("read() <= 0\n");
        }
        else if ( buffer[0x17] == 0x11 ) // UDP
        {
            if ( send(sock_s, buffer ,n ,0)<= 0 )
                printf("write() <= 0 %s\n",strerror(errno));
        }
        fprintf(stdout, "%d %d %d %x %d\n",
n,ntohs(*(short*)(buffer+0x12)),(ntohs(*(short*)(buffer+0x14)) & 0xfff)
<< 3,buffer[0x17],ntohs(*(short*)(buffer+0x24))); fflush(stdout);
    }

    return 0;
}