sender.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#ifdef _WIN32
    #include <Windows.h>
#else
    #include <unistd.h>
#endif

/* If you are building x64 on Windows with WinPcap change add
 * || defined(_WIN64) to #if defined(WIN32) on line 40 */
#include <pcap/pcap.h>

int main(int argc, char **argv)
{
    pcap_t *fp;
    char* endptr = NULL;
    pcap_if_t *alldevs, *d;
    int SLEEP_TIME_MS = 10;
    long index = -1, num_ifaces = 0;
    char errbuf[PCAP_ERRBUF_SIZE + 1];
    unsigned char PAUSE_FRAME[60] =
    {
        0x01, 0x80, 0xC2, 0x00, 0x00, 0x01, /* Destination MAC: Spanning tree for bridges   */
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* Source MAC:      Null                        */
        0x88, 0x08,                         /* EtherType:       MAC control                 */
        0x00, 0x01,                         /* OpCode:			Pause                       */
        0xFF, 0xFF,                         /* pause_time:		65535                       */
                                            /* 42 bytes of padding                          */
    };

    if (pcap_findalldevs(&alldevs, errbuf) == -1)
    {
        fprintf(stderr, "Could not enumerate interfaces: %s\n", errbuf);
        return 1;
    }

    if (argc != 2)
    {
        long counter = 0;

        fprintf(stderr, "Please pass interface name, description, or index on the command line\n\n");

        printf("Index\tName Description\n\n");
        for (d = alldevs; d; d = d->next)
            printf("%ld\t%s %s\n", counter++, d->name, d->description);

        return 1;
    }

    index = strtoul(argv[1], &endptr, 10);
    if (!endptr || *endptr != '\0')
        index = -1;

    for (d = alldevs; d; d = d->next, ++num_ifaces)
    {
        if (index == -1 && 
            ((d->description && (strcmp(d->description, argv[1]) == 0))
                || (d->name && (strcmp(d->name, argv[1]) == 0))))
            index = num_ifaces;
    }

    if (index < 0 || index >= num_ifaces)
    {
        fprintf(stderr, "Could not find interface %s\n", argv[1]);
        return 1;
    }

    d = alldevs;
    while (index--)
        d = d->next;

    if ((fp = pcap_open_live(d->name, 65536, 1, 1000, errbuf)) == NULL)
    {
        fprintf(stderr, "Unable to open the interface: %s\n", errbuf);
        return 1;
    }

    memset(PAUSE_FRAME + 18, 0, 42); /* fill padding with 00 */

    while (1)
    {
        if (pcap_sendpacket(fp, PAUSE_FRAME, sizeof(PAUSE_FRAME)) != 0)
        {
            fprintf(stderr, "Error sending frame: %s\n", pcap_geterr(fp));
            break;
        }

#ifdef _WIN32
        Sleep(SLEEP_TIME_MS);
#else
        usleep(SLEEP_TIME_MS * 1000);
#endif
    }

    pcap_close(fp);
    return 0;
}