Conference star::wizards

1694.0. "Open: why the problem with RAW socket?" by STAR::JKEENAN () Mon Mar 24 1997 13:12

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Remote Info: <null>
Name: Ruslan R. Laishev
Email Address: [email protected]
CPU Architecture: VAX
Version: v 6.1
Questions: 

Dear Wizard !
I'm have write small programm with RAW socket, and when she/he 
running I see  (with TCPIPTRACE utility) what is IP packet's
outgoing and incoming to my HOST.
But I seen also that several fields in IP/TCP packet = -1.
And size of of PACKET realy transmited 60 byte, but I send
40 byte.

Why ?

I'm need more information or any source of C program that 
demonstrate using RAW_IP/SOCK_RAW style socket.

But non-ICMP.

This is as fragment from my programm:
int     SendTCP_SYN (       struct  sockaddr_in *sin,
                        int     s,
                        u_long  baddr,
                        u_short sport,
                        u_long  seq
                )
{
struct  pkt     {
                struct ip       ip_pkt;
                struct tcphdr   tcp;
                } pkt;

struct  stuff   {
                u_long          src;
                u_long          dst;
                char            mbz;
                u_char          proto;
                u_short         len;
                struct  tcphdr  tcp;
                } stuff;

        memset(&pkt,0,sizeof(pkt));

        pkt.ip_pkt.ip_v         = 4;
        pkt.ip_pkt.ip_hl        = 5;
        pkt.ip_pkt.ip_tos       = 0;
        pkt.ip_pkt.ip_len       = htons(sizeof(pkt));
        pkt.ip_pkt.ip_id        = htons (rand() % 2600);
        pkt.ip_pkt.ip_off       = 0;
        pkt.ip_pkt.ip_ttl       = 55;
        pkt.ip_pkt.ip_p         = IPPROTO_TCP;
        pkt.ip_pkt.ip_src.S_un.S_addr = baddr;
        pkt.ip_pkt.ip_dst.S_un.S_addr = sin->sin_addr.S_un.S_addr;
        pkt.ip_pkt.ip_sum       = 0;

        pkt.ip_pkt.ip_sum       = in_cksum(&pkt.ip_pkt, sizeof(pkt.ip_pkt));

        pkt.ip_pkt.ip_sum       = in_cksum(&pkt.ip_pkt, sizeof(pkt.ip_pkt));

        pkt.tcp.th_sport        = htons (sport);
        pkt.tcp.th_dport        = sin->sin_port;
        pkt.tcp.th_seq          = htonl (seq);
        pkt.tcp.th_ack          = 0;
        pkt.tcp.th_x2           = 0;
        pkt.tcp.th_off          = 5;
        pkt.tcp.th_flags        = TH_SYN;
        pkt.tcp.th_win          = htons(10052);
        pkt.tcp.th_sum          = 0;
        pkt.tcp.th_urp          = 0;
        pkt.tcp.th_sum          = 0;


        memset  (&stuff,0,sizeof(stuff));
        stuff.src               = pkt.ip_pkt.ip_src.S_un.S_addr;
        stuff.dst               = pkt.ip_pkt.ip_dst.S_un.S_addr;
        stuff.proto             = pkt.ip_pkt.ip_p;
        stuff.len               = sizeof(pkt.tcp);
        memcpy  (&stuff.tcp,&pkt.tcp,sizeof(pkt.tcp));

        pkt.tcp.th_sum          = in_cksum(&stuff, sizeof(stuff));

        if (0  > sendto (s,&pkt,sizeof(pkt),0,(struct sockaddr *)sin,
                        sizeof(struct sockaddr_in)) )
                perror("sendto");
}

   If looking directly at low-level traffic, one must remember to account
   for the space used for the IP header, and for the TCP or UDP header.
   
   There are various texts and specifications that cover the low-level
   operation of various IP protocols.