无法在ICMPv6数据包中设置Router Alert选项

Question

我试图根据http://www.ietf.org/rfc/rfc3542.txt附录C中指定的示例在发送之前在数据包中设置Hop-By-Hop选项。我在使用API​​时没有看到任何错误，但未在发送的数据包中设置HBH选项。

这是我的代码：

set_rtr_alert_opt (struct msghdr *msg, struct cmsghdr *cmsg)
{
    int         ralen = 0, currentlen = 0;
    void        *hbhbuf = NULL, *optp = NULL;
    u_int8_t    rtr_alert;

    rtr_alert = htons(IP6_ALERT_MLD);

    /*
     * Set the Router Alert option into the cmsg
     */
    ralen = inet6_opt_init(NULL, 0);
    if (ralen == -1) {
        return(FALSE);
    }

    ralen = inet6_opt_append(NULL, 0, ralen, IP6OPT_ROUTER_ALERT, 2,
                             2, NULL);
    if (ralen == -1) {
       return(FALSE);
    }

    ralen = inet6_opt_finish(NULL, 0, ralen);
    if (ralen == -1) {
        return(FALSE);
    }

    cmsg->cmsg_len = CMSG_LEN(ralen);
    cmsg->cmsg_level = IPPROTO_IPV6;
    cmsg->cmsg_type = IPV6_HOPOPTS;
    hbhbuf = CMSG_DATA(cmsg);
    msg->msg_controllen += ALIGN(cmsg->cmsg_len);

    currentlen = inet6_opt_init(hbhbuf, ralen);
    if (currentlen == -1) {
        return(FALSE);
    }

    currentlen = inet6_opt_append(hbhbuf, ralen, currentlen,
                                  IP6OPT_ROUTER_ALERT, 2, 2, &optp);
    if (currentlen == -1) {
        return(FALSE);
    }

    inet6_opt_set_val(optp, 0, &rtr_alert, sizeof(rtr_alert));
    currentlen = inet6_opt_finish(hbhbuf, ralen, currentlen);
    if (currentlen == -1) {
        return(FALSE);
    }

    return(TRUE);
}

在此之后我调用sendmsg（）来发送数据包。数据包确实熄灭但数据包中没有HBH选项。