How to set the IPv6 router alert option in a message - c

Question

I'm working with the RSVP protocol in IPv6 and in order to make it work, I have to set the IPv6 router alert in the messages that I send. I have done lots of research on internet but with no luck, maybe someone here has already done this before. You can find below the code that I use for my tests.
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define DATA_LENGTH 124
int main() {
int data_length = DATA_LENGTH;
unsigned char data[DATA_LENGTH] = {0x10, 0x01, 0xb0, 0x16, 0xff, 0x00, 0x00, 0x7c, 0x00, 0x18,
0x01, 0x02, 0x20, 0x02, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x10, 0x32, 0x00, 0x20, 0xc2, 0x00, 0x18, 0x03, 0x02, 0x20, 0x02, 0x00, 0x01, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x18,
0x0b, 0x02, 0x20, 0x02, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x20, 0x00, 0x00, 0x5d, 0x27, 0x00, 0x08, 0x05, 0x01, 0x00, 0x00, 0x75, 0x30, 0x00, 0x24,
0x0c, 0x02, 0x00, 0x00, 0x00, 0x07, 0x01, 0x00, 0x00, 0x06, 0x7f, 0x00, 0x00, 0x05, 0x49, 0x55,
0x9f, 0x80, 0x4a, 0xba, 0xeb, 0x90, 0x4c, 0xee, 0xa8, 0x31, 0x00, 0x00, 0x00, 0x4b, 0x00, 0x00,
0x05, 0xdc};
unsigned char dest_address[16] = {0x20, 0x01, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0x05};
int socket_descriptor;
struct sockaddr_in6 dest;
const int yes = 1;
const int router_alert_value = 0;
socket_descriptor = socket(AF_INET6, SOCK_RAW, IPPROTO_RSVP);
if (socket_descriptor < 0) {
perror("Can't open socket to send path message\n");
}
memset(&dest, 0, sizeof(dest));
dest.sin6_family = AF_INET6;
memcpy(dest.sin6_addr.s6_addr, dest_address, sizeof(struct in6_addr));
dest.sin6_port = 0;
dest.sin6_flowinfo = 0;
if (setsockopt(socket_descriptor, SOL_SOCKET,
SO_REUSEADDR,(const void *)&yes, sizeof(yes)) < 0) {
printf("setsockopt(%d): %s\n", SO_REUSEADDR, strerror(errno));
}
if(setsockopt(socket_descriptor, IPPROTO_IPV6,
IPV6_HOPOPTS, &yes, sizeof(yes)) < 0) {
printf("Can't set Hop-by-hop Option: %s\n", strerror(errno));
}
if(setsockopt(socket_descriptor, IPPROTO_IPV6, IPV6_ROUTER_ALERT,
(const void *) &router_alert_value, sizeof(router_alert_value)) < 0) {
printf("Can't set IP Options: %s\n", strerror(errno));
}
if(sendto(socket_descriptor, data, data_length, 0,
(struct sockaddr*) &dest, sizeof(dest)) < 0) {
printf("Error in sending message : %s (%d)\n", strerror(errno), errno);
}
close(socket_descriptor);
return(0);
}
The previous code compiles and sends a RSVP Path message but without the IPv6 router alert option. Since I didn't have return when I got errors with the setsockopt method, I could provide you the console output which is:
Can't set Hop-by-hop Option: Invalid argument
Can't set IP Options: Protocol not available
I have done some tries using a socket with the protocol 0 (in order to use the hop-by-hop next header) and by adding the router alert option directly into the data, but it still not working.
Any idea or leads is appreciated.

Answer 1

On Windows with WinSock you can use IPV6_HDRINCL to build the IP header and set the Router Alert flag. On Linux and similar platforms this is simply not available and you would simply have to drop down to raw packets using AF_PACKET similar to Wireshark and tcpdump and hand build artisanal packets to your requirements.
Alternative of course is to propose and implement a new interface in the kernel to set IPv6 Router Alerts.