HI Amit,
To get the option which is already set use the same options. IP_OPTIONS will
not get whether IP_HDRINCL is set or not.
Also while setting options like this, use SOL_IP as socket option level. This
sets the level to IP. Since this Macro is also defined to zero like IPPROTO_IP
you didn't find anything mysterious.
the correct way is
setsockopt(fd, SOL_IP, IP_HDRINCL, &one, sizeof(one));
sameway same arguements for getsockopt also to check whether the options is
set. IP_OPTIONS is only for standard IP header's options. IP_HDRINCL is not of
such kind.
THanks,
Ramesh
Amit Kucheria wrote:
> Hi,
>
> 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.
>
> Sincerely,
> Amit
>
> ---------------- Start of code -----------------------
>
> #include <stdio.h>
> #include <netinet/in.h>
> #include <sys/socket.h>
> #include <netinet/ip.h>
> #include <netinet/tcp.h>
> #define OPTLEN 50
>
> int main(int argc, char *argv[])
> {
> int fd = socket(PF_INET, SOCK_RAW, 48);
> int i;
> int optlen = OPTLEN;
> char optbuff[optlen];
> int one = 1;
> int zero = 0;
>
> if (fd < 0)
> {
> perror("socket");
> exit(1);
> }
>
> printf("Socket created successfully!\n");
>
> /* set socket options to IP_HDRINCL to prevent kernel
> * from including another IP header
> */
> if (setsockopt(fd, IPPROTO_IP, IP_HDRINCL, &one, sizeof(one)) < 0)
> {
> perror("setsockopt: IP_HDRINCL");
> exit(1);
> }
> printf("Socket IP_HDRINCL set!\n");
>
> if (setsockopt(fd, IPPROTO_IP, IP_ROUTER_ALERT, &one, sizeof(one)) < 0)
> {
> perror("setsockopt: IP_ROUTER_ALERT");
> exit(1);
> }
> printf("Socket IP_ROUTER_ALERT set!\n");
>
> memset(optbuff, 0, optlen);
> printf("b4 getsockopt: optlen: %d\n", optlen);
> if (getsockopt(fd, IPPROTO_IP, IP_OPTIONS, optbuff, &optlen) != 0)
> {
> perror("getsockopt");
> exit(1);
> }
>
> /* Print options */
> printf("after getsockopt: optlen: %d\n", optlen);
> for (i=0; i < OPTLEN; i+=2)
> {
> printf("%02x %02x ", optbuff[i], optbuff[i+1]);
> }
> putchar('\n');
>
> return 1;
> }
>
> ---------------- End of code -----------------------
>
> --
> 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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