#include <stdio.h>
#include <string.h>

#include <netinet/in.h>        /* inet_addr() */
#include <arpa/inet.h>

#include <asm/types.h>
#include <sys/socket.h>
#include <linux/netlink.h>        /* netlink ... */
#include <linux/rtnetlink.h>
#include <libnetlink.h>

#define BUFLEN 1024

/* this function forms the netlink packet to add a route to the kernel routing table */
int route_add(__u32* destination, __u32* gateway)
{
    struct rtnl_handle rth;

    /* structure of the netlink packet */
    struct {
        struct nlmsghdr n;
        struct rtmsg r;
        char buf[BUFLEN];
    } req;

    char mxbuf[256];
    struct rtattr *mxrta = (void *)mxbuf;

    memset(&req, 0, sizeof req);

    /* initialisation of few parameters */
    req.n.nlmsg_len = NLMSG_LENGTH(sizeof(struct rtmsg));
    req.n.nlmsg_flags = NLM_F_REQUEST | NLM_F_CREATE;
    req.n.nlmsg_type = RTM_NEWROUTE;
    req.r.rtm_family = AF_INET;
    req.r.rtm_table = RT_TABLE_MAIN;

    req.r.rtm_protocol = RTPROT_BOOT;
    req.r.rtm_scope = RT_SCOPE_UNIVERSE;
    req.r.rtm_type = RTN_UNICAST;

    mxrta->rta_type = RTA_METRICS;
    mxrta->rta_len = RTA_LENGTH(0);

    /* RTA_DST and RTA_GW are the two esential parameters for adding a route,
     * there are other parameters too which are not discussed here.
     * For ipv4, the length of the address is 4 bytes
    */
    addattr_l(&req.n, sizeof req, RTA_DST, destination, 4);
    addattr_l(&req.n, sizeof req, RTA_GATEWAY, gateway, 4);

    /* opening the netlink socket to communicate with the kernel */
    if (rtnl_open(&rth, 0) < 0) {
        fprintf(stderr, "cannot open rtnetlink\n");
        return -1;
    }

    /* sending the packet to the kernel */
    if (rtnl_talk(&rth, &req.n, 0, 0, NULL, NULL, NULL) < 0) {
        return -1;
    }

    return 0;
}

int main(void)
{
    in_addr_t ip, gw;
    ip = inet_addr("192.168.11.100");
    gw = inet_addr("192.168.11.1");

    route_add(&ip, &gw);

    return 0;
}

req.r.rtm_dst_len = 32;    /* IPV4 */