Parse The Received Packet (Cont.)

// verify that it's an ICMP echo request, with the expected seq. num + id.
icmphdr = (struct icmphdr*)(rbuf + (iphdr->ihl * 4));
if (icmphdr->type != ICMP_ECHOREPLY) {
    fprintf(stderr, "Expected ICMP echo-reply, got %u\n", icmphdr->type);
    exit(1);
}
if (icmphdr->un.echo.sequence != 50) {
    fprintf(stderr,
            "Expected sequence 50, got %d\n", icmphdr->un.echo.sequence);
    exit(1);
}
if (icmphdr->un.echo.id != 48) {
    fprintf(stderr,
            "Expected id 48, got %d\n", icmphdr->un.echo.id);
    exit(1);
}
printf("Got the expected ICMP echo-request\n");

Originally written by guy keren