packets dropped by kernel?

[threahdead]

hi.
i was into raw sockets the last time so i wrote a simple
program that would create a single packet and send it
to the destination.

#include <netinet/in.h>
#include <sys/socket.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>

int main ()
{
    int tcp_socket;
    
    struct sockaddr_in peer;
    
    struct send_tcp
    {
	struct iphdr ip;
	struct tcphdr tcp;
    } packet;
    
    packet.ip.version = 4;
    packet.ip.ihl = 5;
    packet.ip.tos = 0;
    packet.ip.tot_len = htons(40);
    packet.ip.id = 1;
    packet.ip.frag_off = 0;
    packet.ip.ttl = 255;
    packet.ip.protocol = IPPROTO_TCP;
    packet.ip.check = 14536;
    packet.ip.saddr = inet_addr("192.168.0.10");
    packet.ip.daddr = inet_addr("192.168.0.1");
    
    
    packet.tcp.source = htons(8000);
    packet.tcp.dest = htons(23);
    packet.tcp.seq = 1;
    packet.tcp.ack_seq = 2;
    packet.tcp.doff = 5;
    packet.tcp.res1 = 0;
    packet.tcp.fin = 0;
    packet.tcp.syn = 1;
    packet.tcp.rst = 0;
    packet.tcp.psh = 0;
    packet.tcp.ack = 0;
    packet.tcp.urg = 0;
    packet.tcp.res2 = 0;
    packet.tcp.window = htons(512);
    packet.tcp.check = 8889;
    packet.tcp.urg_ptr = 0;
    
    peer.sin_family = AF_INET;
    peer.sin_port = htons(25);
    peer.sin_addr.s_addr = inet_addr("192.168.0.1");

	tcp_socket = socket(AF_INET, SOCK_RAW, IPPROTO_RAW);
    
        sendto(tcp_socket, &packet, sizeof(packet), 0, (struct sockaddr *)&peer, sizeof(peer));


	close(tcp_socket);

    return 0;
}

with that code i want to establish a connection to my gateway on port 23. so i switched on tcpdump on the gateway and sent the packet. the was successfully sent but the gateway wasnt replying to that syn packet.
why that?

thanks

ps. i have the port openend i want to connect to.

[orbitz]

You should really use libnet for this sort of thing. Also, read up on TCP/IP. It is alittle bit more complex than I think you believe.

[threahdead]

well i will get some more informations about this topic.
can anyone of you provide an example?
thanks