On Tue, 14 May 2002, Glynn Clements wrote:
>
> Amit Kucheria wrote:
>
> > I have set some IP options for my sockets (IP_HDRINCL & IP_ROUTER_ALERT)
> > using setsockopt(), but when I do a getsockopt(), nothing is reflected.
> > I know I am forgetting something very elementary here, but cant put my
> > finger on it. Any pointers are welcome.
>
> IP_HDRINCL and IP_ROUTER_ALERT aren't "options", in the sense of
> IP_OPTIONS.
So what you mean is that they are not _IP_ options; they are
more of _raw_ socket options?
> Calling getsockopt() on any of the above options should return
> whatever value was set by a preceding setsockopt() call. However, each
> of these options is independent; setting one of them won't change any
> of the others.
>
> Also, if you set both IP_HDRINCL and IP_OPTIONS, IP_OPTIONS is
> ignored.
Then I guess the right question to ask here is:
How can I create an IP packet using raw sockets with the IP_ROUTER_ALERT
option set?
Once I allocate a buffer and fill out the IP and TCP headers, HOW then
should i add the IP_ROUTER_ALERT option and change the length of the IP
header (ip->ihl and ip->tot_len) corresponding to this option.
------ sample code of what i am doing currently -----------
iph = (struct iphdr *)buffer;
tcph = (struct tcphdr *) buffer + sizeof(struct iphdr);
printf("Set pointer to IP and TCP headers!\n");
memset(buffer, 0, PACKET_SIZE); /* zero out the buffer */
/* fill in the ip header */
iph->ihl = 5;
iph->version = 4;
iph->tos = 0;
iph->tot_len = sizeof(struct iphdr)
+ sizeof(struct tcphdr); /* no payload */
iph->id = htonl(23456); /* some value..not imp */
iph->frag_off = 0;
iph->ttl = 255;
iph->protocol = 48; /* protocol: 6 = TCP, 48 = new */
iph->check = 0; /* compute checksum later */
iph->saddr = inet_addr("1.2.3.4"); /* some spoofed src address */
iph->daddr = dest.sin_addr.s_addr;
printf("IP header filled\n");
/* fill in the tcp header */
tcph->source = htons(23456); /* arbit src port */
tcph->dest = htons(P);
tcph->seq = random(); /* random sequence no. */
tcph->ack_seq = 0; /* ack sequence is 0 on first packet */
tcph->res1 = 0; /* unused..reserved */
tcph->doff = 0; /* data offset...used for fragmentation ????? */
tcph->fin = 0;
tcph->syn = 1; /* initial connection request */
tcph->rst = 0;
tcph->psh = 0;
tcph->ack = 0;
tcph->urg = 0;
tcph->res2 = 0; /* unused */
tcph->window = htonl(65535); /* max window size */
tcph->check = 0; /* if set to zero, kernel will fill in correct value
*/
tcph->urg_ptr = 0; /* urgent pointer */
printf("TCP header filled\n");
iph->check = csum((unsigned short *)buffer, iph->tot_len >> 1);
--
I'm an angel!!! Honest!
The horns are just there to hold the halo up straight.
^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^
Amit Kucheria
EECS Grad. Research Assistant
University of Kansas @ Lawrence
(R): +1-785-830-8521 ||| (C): +1-785-760-2871
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