Adding a neighbour with libnl

/* Allocate an empty neighbour handle to be filled out with the attributes
 * of the new neighbour. */
struct rtnl_neigh *neigh = rtnl_neigh_alloc();

/* Fill out the attributes of the new neighbour */
rtnl_neigh_set_ifindex(neigh, ifindex);
rtnl_neigh_set_dst(neigh, dst_addr);
rtnl_neigh_set_state(neigh, rtnl_neigh_str2state("permanent"));

/* Build the netlink message and send it to the kernel, the operation will
 * block until the operation has been completed. Alternatively the required
 * netlink message can be built using rtnl_neigh_build_add_request()
 * to be sent out using nl_send_auto_complete(). */
rtnl_neigh_add(sk, neigh, NLM_F_CREATE);

/* Free the memory */
rtnl_neigh_put(neigh);