text: /*
   * Copyright (c) 2010, Swedish Institute of Computer Science.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. Neither the name of the Institute nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   *
   * This file is part of the Contiki operating system.
   *
   */
  
  /**
   * \file
   *         ICMP6 I/O for RPL control messages.
   *
   * \author Joakim Eriksson <joakime@sics.se>, Nicolas Tsiftes <nvt@sics.se>
   * Contributors: Niclas Finne <nfi@sics.se>, Joel Hoglund <joel@sics.se>,
   *               Mathieu Pouillot <m.pouillot@watteco.com>
   *               George Oikonomou <oikonomou@users.sourceforge.net> (multicast)
   */
  
  /**
   * \addtogroup uip
   * @{
   */
  
  #include "net/ipv6/tcpip.h"
  #include "net/ipv6/uip.h"
  #include "net/ipv6/uip-ds6.h"
  #include "net/ipv6/uip-nd6.h"
  #include "net/ipv6/uip-sr.h"
  #include "net/ipv6/uip-icmp6.h"
  #include "net/routing/rpl-classic/rpl-private.h"
  #include "net/packetbuf.h"
  #include "net/ipv6/multicast/uip-mcast6.h"
  #include "random.h"
  
  #include "sys/log.h"
  
  #include <limits.h>
  #include <string.h>
  
  #define LOG_MODULE "RPL"
  #define LOG_LEVEL LOG_LEVEL_RPL
  
  /*---------------------------------------------------------------------------*/
  #define RPL_DIO_GROUNDED                 0x80
  #define RPL_DIO_MOP_SHIFT                3
  #define RPL_DIO_MOP_MASK                 0x38
  #define RPL_DIO_PREFERENCE_MASK          0x07
  
  /*---------------------------------------------------------------------------*/
  static void dis_input(void);
  static void dio_input(void);
  static void dao_input(void);
  static void dao_ack_input(void);
  
  static void dao_output_target_seq(rpl_parent_t *parent, uip_ipaddr_t *prefix,
                                    uint8_t lifetime, uint8_t seq_no);
  
  /* some debug callbacks useful when debugging RPL networks */
  #ifdef RPL_DEBUG_DIO_INPUT
  void RPL_DEBUG_DIO_INPUT(uip_ipaddr_t *, rpl_dio_t *);
  #endif
  
  #ifdef RPL_DEBUG_DAO_OUTPUT
  void RPL_DEBUG_DAO_OUTPUT(rpl_parent_t *);
  #endif
  
  static uint8_t dao_sequence = RPL_LOLLIPOP_INIT;
  
  #if RPL_WITH_MULTICAST
  static uip_mcast6_route_t *mcast_group;
  #endif
  /*---------------------------------------------------------------------------*/
  /* Initialise RPL ICMPv6 message handlers */
  UIP_ICMP6_HANDLER(dis_handler, ICMP6_RPL, RPL_CODE_DIS, dis_input);
  UIP_ICMP6_HANDLER(dio_handler, ICMP6_RPL, RPL_CODE_DIO, dio_input);
  UIP_ICMP6_HANDLER(dao_handler, ICMP6_RPL, RPL_CODE_DAO, dao_input);
  UIP_ICMP6_HANDLER(dao_ack_handler, ICMP6_RPL, RPL_CODE_DAO_ACK, dao_ack_input);
  /*---------------------------------------------------------------------------*/
  
  #if RPL_WITH_DAO_ACK
  static uip_ds6_route_t *
  find_route_entry_by_dao_ack(uint8_t seq)
  {
    uip_ds6_route_t *re;
    re = uip_ds6_route_head();
    while(re != NULL) {
      if(re->state.dao_seqno_out == seq && RPL_ROUTE_IS_DAO_PENDING(re)) {
        /* found it! */
        return re;
      }
      re = uip_ds6_route_next(re);
    }
    return NULL;
  }
  #endif /* RPL_WITH_DAO_ACK */
  
  #if RPL_WITH_STORING
  /* prepare for forwarding of DAO */
  static uint8_t
  prepare_for_dao_fwd(uint8_t sequence, uip_ds6_route_t *rep)
  {
    /* not pending - or pending but not a retransmission */
    RPL_LOLLIPOP_INCREMENT(dao_sequence);
  
    /* set DAO pending and sequence numbers */
    rep->state.dao_seqno_in = sequence;
    rep->state.dao_seqno_out = dao_sequence;
    RPL_ROUTE_SET_DAO_PENDING(rep);
    return dao_sequence;
  }
  #endif /* RPL_WITH_STORING */
  /*---------------------------------------------------------------------------*/
  static int
  get_global_addr(uip_ipaddr_t *addr)
  {
    int i;
    int state;
    uip_ipaddr_t *prefix = NULL;
    uint8_t prefix_length = 0;
    rpl_dag_t *dag = rpl_get_any_dag();
  
    if(dag != NULL && dag->prefix_info.length != 0) {
      prefix = &dag->prefix_info.prefix;
      prefix_length = dag->prefix_info.length;
    }
  
    for(i = 0; i < UIP_DS6_ADDR_NB; i++) {
      state = uip_ds6_if.addr_list[i].state;
      if(uip_ds6_if.addr_list[i].isused &&
         state == ADDR_PREFERRED &&
         !uip_is_addr_linklocal(&uip_ds6_if.addr_list[i].ipaddr) &&
         (prefix == NULL || uip_ipaddr_prefixcmp(prefix, &uip_ds6_if.addr_list[i].ipaddr, prefix_length))) {
        memcpy(addr, &uip_ds6_if.addr_list[i].ipaddr, sizeof(uip_ipaddr_t));
        return 1;
      }
    }
    return 0;
  }
  /*---------------------------------------------------------------------------*/
  static uint32_t
  get32(uint8_t *buffer, int pos)
  {
    return ((uint32_t)buffer[pos] << 24 | (uint32_t)buffer[pos + 1] << 16 |
            (uint32_t)buffer[pos + 2] << 8 | buffer[pos + 3]);
  }
  /*---------------------------------------------------------------------------*/
  static void
  set32(uint8_t *buffer, int pos, uint32_t value)
  {
    buffer[pos++] = value >> 24;
    buffer[pos++] = (value >> 16) & 0xff;
    buffer[pos++] = (value >> 8) & 0xff;
    buffer[pos++] = value & 0xff;
  }
  /*---------------------------------------------------------------------------*/
  static uint16_t
  get16(uint8_t *buffer, int pos)
  {
    return (uint16_t)buffer[pos] << 8 | buffer[pos + 1];
  }
  /*---------------------------------------------------------------------------*/
  static void
  set16(uint8_t *buffer, int pos, uint16_t value)
  {
    buffer[pos++] = value >> 8;
    buffer[pos++] = value & 0xff;
  }
  /*---------------------------------------------------------------------------*/
  uip_ds6_nbr_t *
  rpl_icmp6_update_nbr_table(uip_ipaddr_t *from, nbr_table_reason_t reason, void *data)
  {
    uip_ds6_nbr_t *nbr;
  
    if((nbr = uip_ds6_nbr_lookup(from)) == NULL) {
      if((nbr = uip_ds6_nbr_add(from, (uip_lladdr_t *)
                                packetbuf_addr(PACKETBUF_ADDR_SENDER),
                                0, NBR_REACHABLE, reason, data)) != NULL) {
        LOG_INFO("Neighbor added to neighbor cache ");
        LOG_INFO_6ADDR(from);
        LOG_INFO_(", ");
        LOG_INFO_LLADDR(packetbuf_addr(PACKETBUF_ADDR_SENDER));
        LOG_INFO_("\n");
      }
    }
  
    return nbr;
  }
  /*---------------------------------------------------------------------------*/
  static void
  dis_input(void)
  {
    rpl_instance_t *instance;
    rpl_instance_t *end;
  
    /* DAG Information Solicitation */
    LOG_INFO("Received a DIS from ");
    LOG_INFO_6ADDR(&UIP_IP_BUF->srcipaddr);
    LOG_INFO_("\n");
  
    for(instance = &instance_table[0], end = instance + RPL_MAX_INSTANCES;
        instance < end; ++instance) {
      if(instance->used == 1) {
        if(uip_is_addr_mcast(&UIP_IP_BUF->destipaddr)) {
  #if RPL_LEAF_ONLY
          LOG_INFO("LEAF ONLY Multicast DIS will NOT reset DIO timer\n");
  #else /* !RPL_LEAF_ONLY */
          LOG_DBG("Multicast DIS => reset DIO timer\n");
          rpl_reset_dio_timer(instance);
  #endif /* !RPL_LEAF_ONLY */
        } else {
          /* Check if this neighbor should be added according to the policy. */
          if(rpl_icmp6_update_nbr_table(&UIP_IP_BUF->srcipaddr,
                                        NBR_TABLE_REASON_RPL_DIS, NULL) == NULL) {
            LOG_ERR("Out of Memory, not sending unicast DIO, DIS from ");
            LOG_ERR_6ADDR(&UIP_IP_BUF->srcipaddr);
            LOG_ERR_(", ");
            LOG_ERR_LLADDR(packetbuf_addr(PACKETBUF_ADDR_SENDER));
            LOG_ERR_("\n");
          } else {
            LOG_DBG("Unicast DIS, reply to sender\n");
            dio_output(instance, &UIP_IP_BUF->srcipaddr);
          }
          /* } */
        }
      }
    }
    uipbuf_clear();
  }
  /*---------------------------------------------------------------------------*/
  void
  dis_output(uip_ipaddr_t *addr)
  {
    unsigned char *buffer;
    uip_ipaddr_t tmpaddr;
  
    /*
     * DAG Information Solicitation  - 2 bytes reserved
     *      0                   1                   2
     *      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
     *     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     *     |     Flags     |   Reserved    |   Option(s)...
     *     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     */
  
    buffer = UIP_ICMP_PAYLOAD;
    buffer[0] = buffer[1] = 0;
  
    if(addr == NULL) {
      uip_create_linklocal_rplnodes_mcast(&tmpaddr);
      addr = &tmpaddr;
    }
  
    LOG_INFO("Sending a DIS to ");
    LOG_INFO_6ADDR(addr);
    LOG_INFO_("\n");
  
    uip_icmp6_send(addr, ICMP6_RPL, RPL_CODE_DIS, 2);
  }
  /*---------------------------------------------------------------------------*/
  static void
  dio_input(void)
  {
    unsigned char *buffer;
    uint8_t buffer_length;
    rpl_dio_t dio;
    uint8_t subopt_type;
    int i;
    int len;
    uip_ipaddr_t from;
  
    memset(&dio, 0, sizeof(dio));
  
    /* Set default values in case the DIO configuration option is missing. */
    dio.dag_intdoubl = RPL_DIO_INTERVAL_DOUBLINGS;
    dio.dag_intmin = RPL_DIO_INTERVAL_MIN;
    dio.dag_redund = RPL_DIO_REDUNDANCY;
    dio.dag_min_hoprankinc = RPL_MIN_HOPRANKINC;
    dio.dag_max_rankinc = RPL_MAX_RANKINC;
    dio.ocp = RPL_OF_OCP;
    dio.default_lifetime = RPL_DEFAULT_LIFETIME;
    dio.lifetime_unit = RPL_DEFAULT_LIFETIME_UNIT;
  
    uip_ipaddr_copy(&from, &UIP_IP_BUF->srcipaddr);
  
    /* DAG Information Object */
    LOG_INFO("Received a DIO from ");
    LOG_INFO_6ADDR(&from);
    LOG_INFO_("\n");
  
    buffer_length = uip_len - uip_l3_icmp_hdr_len;
  
    /* Process the DIO base option. */
    i = 0;
    buffer = UIP_ICMP_PAYLOAD;
  
    dio.instance_id = buffer[i++];
    dio.version = buffer[i++];
    dio.rank = get16(buffer, i);
    i += 2;
  
    LOG_DBG("Incoming DIO (id, ver, rank) = (%u,%u,%u)\n",
           (unsigned)dio.instance_id,
           (unsigned)dio.version,
           (unsigned)dio.rank);
  
    dio.grounded = buffer[i] & RPL_DIO_GROUNDED;
    dio.mop = (buffer[i]& RPL_DIO_MOP_MASK) >> RPL_DIO_MOP_SHIFT;
    dio.preference = buffer[i++] & RPL_DIO_PREFERENCE_MASK;
  
    dio.dtsn = buffer[i++];
    /* two reserved bytes */
    i += 2;
  
    memcpy(&dio.dag_id, buffer + i, sizeof(dio.dag_id));
    i += sizeof(dio.dag_id);
  
    LOG_DBG("Incoming DIO (dag_id, pref) = (");
    LOG_DBG_6ADDR(&dio.dag_id);
    LOG_DBG_(", %u)\n", dio.preference);
  
    /* Check if there are any DIO suboptions. */
    for(; i < buffer_length; i += len) {
      subopt_type = buffer[i];
      if(subopt_type == RPL_OPTION_PAD1) {
        len = 1;
      } else {
        /* Suboption with a two-byte header + payload */
        len = 2 + buffer[i + 1];
      }
  
      if(len + i > buffer_length) {
        LOG_WARN("Invalid DIO packet\n");
        RPL_STAT(rpl_stats.malformed_msgs++);
        goto discard;
      }
  
      LOG_DBG("Incoming DIO (option, length) = (%u, %u)\n", subopt_type, len - 2);
  
      switch(subopt_type) {
        case RPL_OPTION_DAG_METRIC_CONTAINER:
          if(len < 6) {
            LOG_WARN("Invalid DAG MC, len = %d\n", len);
            RPL_STAT(rpl_stats.malformed_msgs++);
            goto discard;
          }
          dio.mc.type = buffer[i + 2];
          dio.mc.flags = buffer[i + 3] << 1;
          dio.mc.flags |= buffer[i + 4] >> 7;
          dio.mc.aggr = (buffer[i + 4] >> 4) & 0x3;
          dio.mc.prec = buffer[i + 4] & 0xf;
          dio.mc.length = buffer[i + 5];
  
          if(dio.mc.type == RPL_DAG_MC_NONE) {
            /* No metric container: do nothing */
          } else if(dio.mc.type == RPL_DAG_MC_ETX) {
            dio.mc.obj.etx = get16(buffer, i + 6);
  
            LOG_DBG("DAG MC: type %u, flags %u, aggr %u, prec %u, length %u, ETX %u\n",
                   (unsigned)dio.mc.type,
                   (unsigned)dio.mc.flags,
                   (unsigned)dio.mc.aggr,
                   (unsigned)dio.mc.prec,
                   (unsigned)dio.mc.length,
                   (unsigned)dio.mc.obj.etx);
          } else if(dio.mc.type == RPL_DAG_MC_ENERGY) {
            dio.mc.obj.energy.flags = buffer[i + 6];
            dio.mc.obj.energy.energy_est = buffer[i + 7];
          } else {
            LOG_WARN("Unhandled DAG MC type: %u\n", (unsigned)dio.mc.type);
            goto discard;
          }
          break;
        case RPL_OPTION_ROUTE_INFO:
          if(len < 9) {
            LOG_WARN("Invalid destination prefix option, len = %d\n", len);
            RPL_STAT(rpl_stats.malformed_msgs++);
            goto discard;
          }
  
          /* The flags field includes the preference value. */
          dio.destination_prefix.length = buffer[i + 2];
          dio.destination_prefix.flags = buffer[i + 3];
          dio.destination_prefix.lifetime = get32(buffer, i + 4);
  
          if(((dio.destination_prefix.length + 7) / 8) + 8 <= len &&
             dio.destination_prefix.length <= 128) {
            LOG_INFO("Copying destination prefix\n");
            memcpy(&dio.destination_prefix.prefix, &buffer[i + 8],
                   (dio.destination_prefix.length + 7) / 8);
          } else {
            LOG_WARN("Invalid route info option, len = %d\n", len);
            RPL_STAT(rpl_stats.malformed_msgs++);
            goto discard;
          }
  
          break;
        case RPL_OPTION_DAG_CONF:
          if(len != 16) {
            LOG_WARN("Invalid DAG configuration option, len = %d\n", len);
            RPL_STAT(rpl_stats.malformed_msgs++);
            goto discard;
          }
  
          /* Path control field not yet implemented - at i + 2 */
          dio.dag_intdoubl = buffer[i + 3];
          dio.dag_intmin = buffer[i + 4];
          dio.dag_redund = buffer[i + 5];
          dio.dag_max_rankinc = get16(buffer, i + 6);
          dio.dag_min_hoprankinc = get16(buffer, i + 8);
          dio.ocp = get16(buffer, i + 10);
          /* buffer + 12 is reserved */
          dio.default_lifetime = buffer[i + 13];
          dio.lifetime_unit = get16(buffer, i + 14);
          LOG_INFO("DAG conf:dbl=%d, min=%d red=%d maxinc=%d mininc=%d ocp=%d d_l=%u l_u=%u\n",
                 dio.dag_intdoubl, dio.dag_intmin, dio.dag_redund,
                 dio.dag_max_rankinc, dio.dag_min_hoprankinc, dio.ocp,
                 dio.default_lifetime, dio.lifetime_unit);
          break;
        case RPL_OPTION_PREFIX_INFO:
          if(len != 32) {
            LOG_WARN("Invalid DAG prefix info, len != 32\n");
            RPL_STAT(rpl_stats.malformed_msgs++);
            goto discard;
          }
          dio.prefix_info.length = buffer[i + 2];
  
          if(dio.prefix_info.length > sizeof(uip_ipaddr_t) * 8) {
            LOG_WARN("Invalid DAG prefix info, len %u > %u\n",
                     dio.prefix_info.length, (unsigned)(sizeof(uip_ipaddr_t) * 8));
            RPL_STAT(rpl_stats.malformed_msgs++);
            goto discard;
          }
  
          dio.prefix_info.flags = buffer[i + 3];
          /* valid lifetime is ingnored for now - at i + 4 */
          /* preferred lifetime stored in lifetime */
          dio.prefix_info.lifetime = get32(buffer, i + 8);
          /* 32-bit reserved at i + 12 */
          LOG_INFO("Copying prefix information\n");
          memcpy(&dio.prefix_info.prefix, &buffer[i + 16], 16);
          break;
        default:
          LOG_WARN("Unsupported suboption type in DIO: %u\n",
                 (unsigned)subopt_type);
      }
    }
  
  #ifdef RPL_DEBUG_DIO_INPUT
    RPL_DEBUG_DIO_INPUT(&from, &dio);
  #endif
  
    rpl_process_dio(&from, &dio);
  
  discard:
    uipbuf_clear();
  }
  /*---------------------------------------------------------------------------*/
  void
  dio_output(rpl_instance_t *instance, uip_ipaddr_t *uc_addr)
  {
    unsigned char *buffer;
    int pos;
    int is_root;
    rpl_dag_t *dag = instance->current_dag;
  #if !RPL_LEAF_ONLY
    uip_ipaddr_t addr;
  #endif /* !RPL_LEAF_ONLY */
  
  #if RPL_LEAF_ONLY
    /* In leaf mode, we only send DIO messages as unicasts in response to
       unicast DIS messages. */
    if(uc_addr == NULL) {
      LOG_DBG("LEAF ONLY have multicast addr: skip dio_output\n");
      return;
    }
  #endif /* RPL_LEAF_ONLY */
  
    /* DAG Information Object */
    pos = 0;
  
    buffer = UIP_ICMP_PAYLOAD;
    buffer[pos++] = instance->instance_id;
    buffer[pos++] = dag->version;
    is_root = (dag->rank == ROOT_RANK(instance));
  
  #if RPL_LEAF_ONLY
    LOG_DBG("LEAF ONLY DIO rank set to RPL_INFINITE_RANK\n");
    set16(buffer, pos, RPL_INFINITE_RANK);
  #else /* RPL_LEAF_ONLY */
    set16(buffer, pos, dag->rank);
  #endif /* RPL_LEAF_ONLY */
    pos += 2;
  
    buffer[pos] = 0;
    if(dag->grounded) {
      buffer[pos] |= RPL_DIO_GROUNDED;
    }
  
    buffer[pos] |= instance->mop << RPL_DIO_MOP_SHIFT;
    buffer[pos] |= dag->preference & RPL_DIO_PREFERENCE_MASK;
    pos++;
  
    buffer[pos++] = instance->dtsn_out;
  
    if(RPL_DIO_REFRESH_DAO_ROUTES && is_root && uc_addr == NULL) {
      /* Request new DAO to refresh route. We do not do this for unicast DIO
       * in order to avoid DAO messages after a DIS-DIO update,
       * or upon unicast DIO probing. */
      RPL_LOLLIPOP_INCREMENT(instance->dtsn_out);
    }
  
    /* reserved 2 bytes */
    buffer[pos++] = 0; /* flags */
    buffer[pos++] = 0; /* reserved */
  
    memcpy(buffer + pos, &dag->dag_id, sizeof(dag->dag_id));
    pos += 16;
  
  #if !RPL_LEAF_ONLY
    if(instance->mc.type != RPL_DAG_MC_NONE) {
      instance->of->update_metric_container(instance);
  
      buffer[pos++] = RPL_OPTION_DAG_METRIC_CONTAINER;
      buffer[pos++] = 6;
      buffer[pos++] = instance->mc.type;
      buffer[pos++] = instance->mc.flags >> 1;
      buffer[pos] = (instance->mc.flags & 1) << 7;
      buffer[pos++] |= (instance->mc.aggr << 4) | instance->mc.prec;
      if(instance->mc.type == RPL_DAG_MC_ETX) {
        buffer[pos++] = 2;
        set16(buffer, pos, instance->mc.obj.etx);
        pos += 2;
      } else if(instance->mc.type == RPL_DAG_MC_ENERGY) {
        buffer[pos++] = 2;
        buffer[pos++] = instance->mc.obj.energy.flags;
        buffer[pos++] = instance->mc.obj.energy.energy_est;
      } else {
        LOG_ERR("Unable to send DIO because of unhandled DAG MC type %u\n",
               (unsigned)instance->mc.type);
        return;
      }
    }
  #endif /* !RPL_LEAF_ONLY */
  
    /* Always add a DAG configuration option. */
    buffer[pos++] = RPL_OPTION_DAG_CONF;
    buffer[pos++] = 14;
    buffer[pos++] = 0; /* No Auth, PCS = 0 */
    buffer[pos++] = instance->dio_intdoubl;
    buffer[pos++] = instance->dio_intmin;
    buffer[pos++] = instance->dio_redundancy;
    set16(buffer, pos, instance->max_rankinc);
    pos += 2;
    set16(buffer, pos, instance->min_hoprankinc);
    pos += 2;
    /* OCP is in the DAG_CONF option */
    set16(buffer, pos, instance->of->ocp);
    pos += 2;
    buffer[pos++] = 0; /* reserved */
    buffer[pos++] = instance->default_lifetime;
    set16(buffer, pos, instance->lifetime_unit);
    pos += 2;
  
    /* Check if we have a prefix to send also. */
    if(dag->prefix_info.length > 0) {
      buffer[pos++] = RPL_OPTION_PREFIX_INFO;
      buffer[pos++] = 30; /* always 30 bytes + 2 long */
      buffer[pos++] = dag->prefix_info.length;
      buffer[pos++] = dag->prefix_info.flags;
      set32(buffer, pos, dag->prefix_info.lifetime);
      pos += 4;
      set32(buffer, pos, dag->prefix_info.lifetime);
      pos += 4;
      memset(&buffer[pos], 0, 4);
      pos += 4;
      memcpy(&buffer[pos], &dag->prefix_info.prefix, 16);
      pos += 16;
      LOG_DBG("Sending prefix info in DIO for ");
      LOG_DBG_6ADDR(&dag->prefix_info.prefix);
      LOG_DBG_("\n");
    } else {
      LOG_DBG("No prefix to announce (len %d)\n",
             dag->prefix_info.length);
    }
  
  #if RPL_LEAF_ONLY
    if(LOG_DBG_ENABLED) {
      if(uc_addr == NULL) {
        LOG_DBG("LEAF ONLY sending unicast-DIO from multicast-DIO\n");
      }
    }
  
    LOG_INFO("Sending unicast-DIO with rank %u to ",
           (unsigned)dag->rank);
    LOG_INFO_6ADDR(uc_addr);
    LOG_INFO_("\n");
    uip_icmp6_send(uc_addr, ICMP6_RPL, RPL_CODE_DIO, pos);
  #else /* RPL_LEAF_ONLY */
    /* Unicast requests get unicast replies! */
    if(uc_addr == NULL) {
      LOG_INFO("Sending a multicast-DIO with rank %u\n",
             (unsigned)instance->current_dag->rank);
      uip_create_linklocal_rplnodes_mcast(&addr);
      uip_icmp6_send(&addr, ICMP6_RPL, RPL_CODE_DIO, pos);
    } else {
      LOG_INFO("Sending unicast-DIO with rank %u to ",
             (unsigned)instance->current_dag->rank);
      LOG_INFO_6ADDR(uc_addr);
      LOG_INFO_("\n");
      uip_icmp6_send(uc_addr, ICMP6_RPL, RPL_CODE_DIO, pos);
    }
  #endif /* RPL_LEAF_ONLY */
  }
  /*---------------------------------------------------------------------------*/
  static void
  dao_input_storing(void)
  {
  #if RPL_WITH_STORING
    uip_ipaddr_t dao_sender_addr;
    rpl_dag_t *dag;
    rpl_instance_t *instance;
    unsigned char *buffer;
    uint16_t sequence;
    uint8_t instance_id;
    uint8_t lifetime;
    uint8_t prefixlen;
    uint8_t flags;
    uint8_t subopt_type;
    /*
      uint8_t pathcontrol;
      uint8_t pathsequence;
    */
    uip_ipaddr_t prefix;
    uip_ds6_route_t *rep;
    uint8_t buffer_length;
    int pos;
    int len;
    int i;
    int learned_from;
    rpl_parent_t *parent;
    uip_ds6_nbr_t *nbr;
    int is_root;
  
    prefixlen = 0;
    parent = NULL;
    memset(&prefix, 0, sizeof(prefix));
  
    uip_ipaddr_copy(&dao_sender_addr, &UIP_IP_BUF->srcipaddr);
  
    buffer = UIP_ICMP_PAYLOAD;
    buffer_length = uip_len - uip_l3_icmp_hdr_len;
  
    pos = 0;
    instance_id = buffer[pos++];
  
    instance = rpl_get_instance(instance_id);
  
    lifetime = instance->default_lifetime;
  
    flags = buffer[pos++];
    /* reserved */
    pos++;
    sequence = buffer[pos++];
  
    dag = instance->current_dag;
    is_root = (dag->rank == ROOT_RANK(instance));
  
    /* Is the DAG ID present? */
    if(flags & RPL_DAO_D_FLAG) {
      if(memcmp(&dag->dag_id, &buffer[pos], sizeof(dag->dag_id))) {
        LOG_INFO("Ignoring a DAO for a DAG different from ours\n");
        return;
      }
      pos += 16;
    }
  
    learned_from = uip_is_addr_mcast(&dao_sender_addr) ?
      RPL_ROUTE_FROM_MULTICAST_DAO : RPL_ROUTE_FROM_UNICAST_DAO;
  
    /* Destination Advertisement Object */
    LOG_DBG("Received a (%s) DAO with sequence number %u from ",
           learned_from == RPL_ROUTE_FROM_UNICAST_DAO? "unicast": "multicast", sequence);
    LOG_DBG_6ADDR(&dao_sender_addr);
    LOG_DBG_("\n");
  
    if(learned_from == RPL_ROUTE_FROM_UNICAST_DAO) {
      /* Check whether this is a DAO forwarding loop. */
      parent = rpl_find_parent(dag, &dao_sender_addr);
      /* check if this is a new DAO registration with an "illegal" rank */
      /* if we already route to this node it is likely */
      if(parent != NULL &&
         DAG_RANK(parent->rank, instance) < DAG_RANK(dag->rank, instance)) {
        LOG_WARN("Loop detected when receiving a unicast DAO from a node with a lower rank! (%u < %u)\n",
               DAG_RANK(parent->rank, instance), DAG_RANK(dag->rank, instance));
        parent->rank = RPL_INFINITE_RANK;
        parent->flags |= RPL_PARENT_FLAG_UPDATED;
        return;
      }
  
      /* If we get the DAO from our parent, we also have a loop. */
      if(parent != NULL && parent == dag->preferred_parent) {
        LOG_WARN("Loop detected when receiving a unicast DAO from our parent\n");
        parent->rank = RPL_INFINITE_RANK;
        parent->flags |= RPL_PARENT_FLAG_UPDATED;
        return;
      }
    }
  
    /* Check if there are any RPL options present. */
    for(i = pos; i < buffer_length; i += len) {
      subopt_type = buffer[i];
      if(subopt_type == RPL_OPTION_PAD1) {
        len = 1;
      } else {
        /* The option consists of a two-byte header and a payload. */
        len = 2 + buffer[i + 1];
      }
  
      switch(subopt_type) {
        case RPL_OPTION_TARGET:
          /* Handle the target option. */
          prefixlen = buffer[i + 3];
          if(prefixlen == 0) {
            /* Ignore option targets with a prefix length of 0. */
            break;
          }
          if(prefixlen > 128) {
            LOG_ERR("Too large target prefix length %d\n", prefixlen);
            return;
          }
          if(i + 4 + ((prefixlen + 7) / CHAR_BIT) > buffer_length) {
            LOG_ERR("Insufficient space to copy RPL Target of %d bits\n",
                    prefixlen);
            return;
          }
          memset(&prefix, 0, sizeof(prefix));
          memcpy(&prefix, buffer + i + 4, (prefixlen + 7) / CHAR_BIT);
          break;
        case RPL_OPTION_TRANSIT:
          /* The path sequence and control are ignored. */
          /*      pathcontrol = buffer[i + 3];
                  pathsequence = buffer[i + 4];*/
          lifetime = buffer[i + 5];
          /* The parent address is also ignored. */
          break;
      }
    }
  
    LOG_INFO("DAO lifetime: %u, prefix length: %u prefix: ",
           (unsigned)lifetime, (unsigned)prefixlen);
    LOG_INFO_6ADDR(&prefix);
    LOG_INFO_("\n");
  
  #if RPL_WITH_MULTICAST
    if(uip_is_addr_mcast_global(&prefix)) {
      /*
       * "rep" is used for a unicast route which we don't need now; so set NULL so
       * that operations on "rep" will be skipped.
       */
      rep = NULL;
      mcast_group = uip_mcast6_route_add(&prefix);
      if(mcast_group) {
        mcast_group->dag = dag;
        mcast_group->lifetime = RPL_LIFETIME(instance, lifetime);
      }
      goto fwd_dao;
    }
  #endif
  
    rep = uip_ds6_route_lookup(&prefix);
  
    if(lifetime == RPL_ZERO_LIFETIME) {
      LOG_INFO("No-Path DAO received\n");
      /* No-Path DAO received; invoke the route purging routine. */
      if(rep != NULL &&
         !RPL_ROUTE_IS_NOPATH_RECEIVED(rep) &&
         rep->length == prefixlen &&
         uip_ds6_route_nexthop(rep) != NULL &&
         uip_ipaddr_cmp(uip_ds6_route_nexthop(rep), &dao_sender_addr)) {
        LOG_DBG("Setting expiration timer for prefix ");
        LOG_DBG_6ADDR(&prefix);
        LOG_DBG_("\n");
        RPL_ROUTE_SET_NOPATH_RECEIVED(rep);
        rep->state.lifetime = RPL_NOPATH_REMOVAL_DELAY;
  
        /* We forward the incoming No-Path DAO to our parent, if we have
           one. */
        if(dag->preferred_parent != NULL &&
           rpl_parent_get_ipaddr(dag->preferred_parent) != NULL) {
          uint8_t out_seq;
          out_seq = prepare_for_dao_fwd(sequence, rep);
  
          LOG_DBG("Forwarding No-path DAO to parent - out_seq:%d",
                 out_seq);
          LOG_DBG_6ADDR(rpl_parent_get_ipaddr(dag->preferred_parent));
          LOG_DBG_("\n");
  
          buffer = UIP_ICMP_PAYLOAD;
          buffer[3] = out_seq; /* add an outgoing seq no before fwd */
          uip_icmp6_send(rpl_parent_get_ipaddr(dag->preferred_parent),
                         ICMP6_RPL, RPL_CODE_DAO, buffer_length);
        }
      }
      /* independent if we remove or not - ACK the request */
      if(flags & RPL_DAO_K_FLAG) {
        /* indicate that we accepted the no-path DAO */
        uipbuf_clear();
        dao_ack_output(instance, &dao_sender_addr, sequence,
                       RPL_DAO_ACK_UNCONDITIONAL_ACCEPT);
      }
      return;
    }
  
    LOG_INFO("Adding DAO route\n");
  
    /* Update and add neighbor - if no room - fail. */
    if((nbr = rpl_icmp6_update_nbr_table(&dao_sender_addr, NBR_TABLE_REASON_RPL_DAO, instance)) == NULL) {
      LOG_ERR("Out of Memory, dropping DAO from ");
      LOG_ERR_6ADDR(&dao_sender_addr);
      LOG_ERR_(", ");
      LOG_ERR_LLADDR(packetbuf_addr(PACKETBUF_ADDR_SENDER));
      LOG_ERR_("\n");
      if(flags & RPL_DAO_K_FLAG) {
        /* signal the failure to add the node */
        dao_ack_output(instance, &dao_sender_addr, sequence,
                       is_root ? RPL_DAO_ACK_UNABLE_TO_ADD_ROUTE_AT_ROOT :
                       RPL_DAO_ACK_UNABLE_TO_ACCEPT);
      }
      return;
    }
  
    rep = rpl_add_route(dag, &prefix, prefixlen, &dao_sender_addr);
    if(rep == NULL) {
      RPL_STAT(rpl_stats.mem_overflows++);
      LOG_ERR("Could not add a route after receiving a DAO\n");
      if(flags & RPL_DAO_K_FLAG) {
        /* signal the failure to add the node */
        dao_ack_output(instance, &dao_sender_addr, sequence,
                       is_root ? RPL_DAO_ACK_UNABLE_TO_ADD_ROUTE_AT_ROOT :
                       RPL_DAO_ACK_UNABLE_TO_ACCEPT);
      }
      return;
    }
  
    /* set lifetime and clear NOPATH bit */
    rep->state.lifetime = RPL_LIFETIME(instance, lifetime);
    RPL_ROUTE_CLEAR_NOPATH_RECEIVED(rep);
  
  #if RPL_WITH_MULTICAST
  fwd_dao:
  #endif
  
    if(learned_from == RPL_ROUTE_FROM_UNICAST_DAO) {
      int should_ack = 0;
  
      if(flags & RPL_DAO_K_FLAG) {
        if(rep != NULL) {
          /*
           * check if this route is already installed and we can ack now!
           * not pending - and same seq-no means that we can ack.
           * (e.g. the route is installed already so it will not take any
           * more room that it already takes - so should be ok!)
           */
          if((!RPL_ROUTE_IS_DAO_PENDING(rep) &&
              rep->state.dao_seqno_in == sequence) ||
             dag->rank == ROOT_RANK(instance)) {
            should_ack = 1;
          }
        }
      }
  
      if(dag->preferred_parent != NULL &&
         rpl_parent_get_ipaddr(dag->preferred_parent) != NULL) {
        uint8_t out_seq = 0;
        if(rep != NULL) {
          /* if this is pending and we get the same seq no it is a retrans */
          if(RPL_ROUTE_IS_DAO_PENDING(rep) &&
             rep->state.dao_seqno_in == sequence) {
            /* keep the same seq-no as before for parent also */
            out_seq = rep->state.dao_seqno_out;
          } else {
            out_seq = prepare_for_dao_fwd(sequence, rep);
          }
        }
  
        LOG_DBG("Forwarding DAO to parent ");
        LOG_DBG_6ADDR(rpl_parent_get_ipaddr(dag->preferred_parent));
        LOG_DBG_(" in seq: %d out seq: %d\n", sequence, out_seq);
  
        buffer = UIP_ICMP_PAYLOAD;
        buffer[3] = out_seq; /* add an outgoing seq no before fwd */
        uip_icmp6_send(rpl_parent_get_ipaddr(dag->preferred_parent),
                       ICMP6_RPL, RPL_CODE_DAO, buffer_length);
      }
      if(should_ack) {
        LOG_DBG("Sending DAO ACK\n");
        uipbuf_clear();
        dao_ack_output(instance, &dao_sender_addr, sequence,
                       RPL_DAO_ACK_UNCONDITIONAL_ACCEPT);
      }
    }
  #endif /* RPL_WITH_STORING */
  }
  /*---------------------------------------------------------------------------*/
  static void
  dao_input_nonstoring(void)
  {
  #if RPL_WITH_NON_STORING
    uip_ipaddr_t dao_sender_addr;
    uip_ipaddr_t dao_parent_addr;
    rpl_dag_t *dag;
    rpl_instance_t *instance;
    unsigned char *buffer;
    uint16_t sequence;
    uint8_t instance_id;
    uint8_t lifetime;
    uint8_t prefixlen;
    uint8_t flags;
    uint8_t subopt_type;
    uip_ipaddr_t prefix;
    uint8_t buffer_length;
    int pos;
    int len;
    int i;
  
    /* Destination Advertisement Object */
    LOG_INFO("Received a DAO from ");
    LOG_INFO_6ADDR(&UIP_IP_BUF->srcipaddr);
    LOG_INFO_("\n");
  
    prefixlen = 0;
  
    uip_ipaddr_copy(&dao_sender_addr, &UIP_IP_BUF->srcipaddr);
    memset(&dao_parent_addr, 0, 16);
  
    buffer = UIP_ICMP_PAYLOAD;
    buffer_length = uip_len - uip_l3_icmp_hdr_len;
  
    pos = 0;
    instance_id = buffer[pos++];
    instance = rpl_get_instance(instance_id);
    lifetime = instance->default_lifetime;
  
    flags = buffer[pos++];
    /* reserved */
    pos++;
    sequence = buffer[pos++];
  
    dag = instance->current_dag;
    /* Is the DAG ID present? */
    if(flags & RPL_DAO_D_FLAG) {
      if(memcmp(&dag->dag_id, &buffer[pos], sizeof(dag->dag_id))) {
        LOG_INFO("Ignoring a DAO for a DAG different from ours\n");
        return;
      }
      pos += 16;
    }
  
    /* Check if there are any RPL options present. */
    for(i = pos; i < buffer_length; i += len) {
      subopt_type = buffer[i];
      if(subopt_type == RPL_OPTION_PAD1) {
        len = 1;
      } else {
        /* The option consists of a two-byte header and a payload. */
        len = 2 + buffer[i + 1];
      }
  
      switch(subopt_type) {
        case RPL_OPTION_TARGET:
          /* Handle the target option. */
          prefixlen = buffer[i + 3];
          if(prefixlen == 0) {
            /* Ignore option targets with a prefix length of 0. */
            break;
          }
          if(prefixlen > 128) {
            LOG_ERR("Too large target prefix length %d\n", prefixlen);
            return;
          }
          if(i + 4 + ((prefixlen + 7) / CHAR_BIT) > buffer_length) {
            LOG_ERR("Insufficient space to copy RPL Target of %d bits\n",
                    prefixlen);
            return;
          }
          memset(&prefix, 0, sizeof(prefix));
          memcpy(&prefix, buffer + i + 4, (prefixlen + 7) / CHAR_BIT);
          break;
        case RPL_OPTION_TRANSIT:
          /* The path sequence and control are ignored. */
          /*      pathcontrol = buffer[i + 3];
                  pathsequence = buffer[i + 4];*/
          lifetime = buffer[i + 5];
          if(len >= 20) {
            memcpy(&dao_parent_addr, buffer + i + 6, 16);
          }
          break;
      }
    }
  
    LOG_INFO("DAO lifetime: %u, prefix length: %u prefix: ",
           (unsigned)lifetime, (unsigned)prefixlen);
    LOG_INFO_6ADDR(&prefix);
    LOG_INFO_(", parent: ");
    LOG_INFO_6ADDR(&dao_parent_addr);
    LOG_INFO_("\n");
  
    if(lifetime == RPL_ZERO_LIFETIME) {
      LOG_DBG("No-Path DAO received\n");
      uip_sr_expire_parent(dag, &prefix, &dao_parent_addr);
    } else {
      if(uip_sr_update_node(dag, &prefix, &dao_parent_addr, RPL_LIFETIME(instance, lifetime)) == NULL) {
        LOG_WARN("DAO failed to add link prefix: ");
        LOG_WARN_6ADDR(&prefix);
        LOG_WARN_(", parent: ");
        LOG_WARN_6ADDR(&dao_parent_addr);
        LOG_WARN_("\n");
        return;
      }
    }
  
    if(flags & RPL_DAO_K_FLAG) {
      LOG_DBG("Sending DAO ACK\n");
      uipbuf_clear();
      dao_ack_output(instance, &dao_sender_addr, sequence,
                     RPL_DAO_ACK_UNCONDITIONAL_ACCEPT);
    }
  #endif /* RPL_WITH_NON_STORING */
  }
  /*---------------------------------------------------------------------------*/
  static void
  dao_input(void)
  {
    rpl_instance_t *instance;
    uint8_t instance_id;
  
    /* Destination Advertisement Object */
    LOG_INFO("Received a DAO from ");
    LOG_INFO_6ADDR(&UIP_IP_BUF->srcipaddr);
    LOG_INFO_("\n");
  
    instance_id = UIP_ICMP_PAYLOAD[0];
    instance = rpl_get_instance(instance_id);
    if(instance == NULL) {
      LOG_INFO("Ignoring a DAO for an unknown RPL instance(%u)\n",
             instance_id);
      goto discard;
    }
  
    if(RPL_IS_STORING(instance)) {
      dao_input_storing();
    } else if(RPL_IS_NON_STORING(instance)) {
      dao_input_nonstoring();
    }
  
  discard:
    uipbuf_clear();
  }
  /*---------------------------------------------------------------------------*/
  #if RPL_WITH_DAO_ACK
  static void
  handle_dao_retransmission(void *ptr)
  {
    rpl_parent_t *parent;
    uip_ipaddr_t prefix;
    rpl_instance_t *instance;
  
    parent = ptr;
    if(parent == NULL || parent->dag == NULL || parent->dag->instance == NULL) {
      return;
    }
    instance = parent->dag->instance;
  
    if(instance->my_dao_transmissions >= RPL_DAO_MAX_RETRANSMISSIONS) {
      /* No more retransmissions - give up. */
      if(instance->lifetime_unit == 0xffff && instance->default_lifetime == 0xff) {
        /*
         * ContikiRPL was previously using infinite lifetime for routes
         * and no DAO_ACK configured. This probably means that the root
         * and possibly other nodes might be running an old version that
         * does not support DAO ack. Assume that everything is ok for
         * now and let the normal repair mechanisms detect any problems.
         */
        return;
      }
  
      if(RPL_IS_STORING(instance) && instance->of->dao_ack_callback) {
        /* Inform the objective function about the timeout. */
        instance->of->dao_ack_callback(parent, RPL_DAO_ACK_TIMEOUT);
      }
  
      /* Perform local repair and hope to find another parent. */
      rpl_local_repair(instance);
      return;
    }
  
    LOG_INFO("will retransmit DAO - seq:%d trans:%d\n", instance->my_dao_seqno,
           instance->my_dao_transmissions);
  
    if(get_global_addr(&prefix) == 0) {
      return;
    }
  
    ctimer_set(&instance->dao_retransmit_timer,
               RPL_DAO_RETRANSMISSION_TIMEOUT / 2 +
               (random_rand() % (RPL_DAO_RETRANSMISSION_TIMEOUT / 2)),
               handle_dao_retransmission, parent);
  
    instance->my_dao_transmissions++;
    dao_output_target_seq(parent, &prefix,
                          instance->default_lifetime, instance->my_dao_seqno);
  }
  #endif /* RPL_WITH_DAO_ACK */
  /*---------------------------------------------------------------------------*/
  void
  dao_output(rpl_parent_t *parent, uint8_t lifetime)
  {
    /* Destination Advertisement Object */
    uip_ipaddr_t prefix;
  
    if(get_global_addr(&prefix) == 0) {
      LOG_ERR("No global address set for this node - suppressing DAO\n");
      return;
    }
  
    if(parent == NULL || parent->dag == NULL || parent->dag->instance == NULL) {
      return;
    }
  
    RPL_LOLLIPOP_INCREMENT(dao_sequence);
  #if RPL_WITH_DAO_ACK
    /* set up the state since this will be the first transmission of DAO */
    /* retransmissions will call directly to dao_output_target_seq */
    /* keep track of my own sending of DAO for handling ack and loss of ack */
    if(lifetime != RPL_ZERO_LIFETIME) {
      rpl_instance_t *instance;
      instance = parent->dag->instance;
  
      instance->my_dao_seqno = dao_sequence;
      instance->my_dao_transmissions = 1;
      ctimer_set(&instance->dao_retransmit_timer, RPL_DAO_RETRANSMISSION_TIMEOUT,
                 handle_dao_retransmission, parent);
    }
  #else
    /* We know that we have tried to register so now we are assuming
       that we have a down-link - unless this is a zero lifetime one */
    parent->dag->instance->has_downward_route = lifetime != RPL_ZERO_LIFETIME;
  #endif /* RPL_WITH_DAO_ACK */
  
    /* Sending a DAO with own prefix as target */
    dao_output_target(parent, &prefix, lifetime);
  }
  /*---------------------------------------------------------------------------*/
  void
  dao_output_target(rpl_parent_t *parent, uip_ipaddr_t *prefix, uint8_t lifetime)
  {
    dao_output_target_seq(parent, prefix, lifetime, dao_sequence);
  }
  /*---------------------------------------------------------------------------*/
  static void
  dao_output_target_seq(rpl_parent_t *parent, uip_ipaddr_t *prefix,
                        uint8_t lifetime, uint8_t seq_no)
  {
    rpl_dag_t *dag;
    rpl_instance_t *instance;
    unsigned char *buffer;
    uint8_t prefixlen;
    int pos;
    uip_ipaddr_t *parent_ipaddr = NULL;
    uip_ipaddr_t *dest_ipaddr = NULL;
  
    /* Destination Advertisement Object */
  
    /* If we are in feather mode, we should not send any DAOs */
    if(rpl_get_mode() == RPL_MODE_FEATHER) {
      return;
    }
  
    if(parent == NULL) {
      LOG_ERR("dao_output_target error parent NULL\n");
      return;
    }
  
    parent_ipaddr = rpl_parent_get_ipaddr(parent);
    if(parent_ipaddr == NULL) {
      LOG_ERR("dao_output_target error parent IP address NULL\n");
      return;
    }
  
    dag = parent->dag;
    if(dag == NULL) {
      LOG_ERR("dao_output_target error dag NULL\n");
      return;
    }
  
    instance = dag->instance;
  
    if(instance == NULL) {
      LOG_ERR("dao_output_target error instance NULL\n");
      return;
    }
    if(prefix == NULL) {
      LOG_ERR("dao_output_target error prefix NULL\n");
      return;
    }
  #ifdef RPL_DEBUG_DAO_OUTPUT
    RPL_DEBUG_DAO_OUTPUT(parent);
  #endif
  
    buffer = UIP_ICMP_PAYLOAD;
    pos = 0;
  
    buffer[pos++] = instance->instance_id;
    buffer[pos] = 0;
  #if RPL_DAO_SPECIFY_DAG
    buffer[pos] |= RPL_DAO_D_FLAG;
  #endif /* RPL_DAO_SPECIFY_DAG */
  #if RPL_WITH_DAO_ACK
    if(lifetime != RPL_ZERO_LIFETIME) {
      buffer[pos] |= RPL_DAO_K_FLAG;
    }
  #endif /* RPL_WITH_DAO_ACK */
    ++pos;
    buffer[pos++] = 0; /* reserved */
    buffer[pos++] = seq_no;
  #if RPL_DAO_SPECIFY_DAG
    memcpy(buffer + pos, &dag->dag_id, sizeof(dag->dag_id));
    pos+=sizeof(dag->dag_id);
  #endif /* RPL_DAO_SPECIFY_DAG */
  
    /* create target subopt */
    prefixlen = sizeof(*prefix) * CHAR_BIT;
    buffer[pos++] = RPL_OPTION_TARGET;
    buffer[pos++] = 2 + ((prefixlen + 7) / CHAR_BIT);
    buffer[pos++] = 0; /* reserved */
    buffer[pos++] = prefixlen;
    memcpy(buffer + pos, prefix, (prefixlen + 7) / CHAR_BIT);
    pos += ((prefixlen + 7) / CHAR_BIT);
  
    /* Create a transit information sub-option. */
    buffer[pos++] = RPL_OPTION_TRANSIT;
    buffer[pos++] = (instance->mop != RPL_MOP_NON_STORING) ? 4 : 20;
    buffer[pos++] = 0; /* flags - ignored */
    buffer[pos++] = 0; /* path control - ignored */
    buffer[pos++] = 0; /* path seq - ignored */
    buffer[pos++] = lifetime;
  
    if(instance->mop != RPL_MOP_NON_STORING) {
      /* Send DAO to parent */
      dest_ipaddr = parent_ipaddr;
    } else {
      /* Include parent global IP address */
      memcpy(buffer + pos, &parent->dag->dag_id, 8); /* Prefix */
      pos += 8;
      memcpy(buffer + pos, ((const unsigned char *)parent_ipaddr) + 8, 8); /* Interface identifier */
      pos += 8;
      /* Send DAO to root */
      dest_ipaddr = &parent->dag->dag_id;
    }
  
    LOG_INFO("Sending a %sDAO with sequence number %u, lifetime %u, prefix ",
           lifetime == RPL_ZERO_LIFETIME ? "No-Path " : "", seq_no, lifetime);
  
    LOG_INFO_6ADDR(prefix);
    LOG_INFO_(" to ");
    LOG_INFO_6ADDR(dest_ipaddr);
    LOG_INFO_(" , parent ");
    LOG_INFO_6ADDR(parent_ipaddr);
    LOG_INFO_("\n");
  
    if(dest_ipaddr != NULL) {
      uip_icmp6_send(dest_ipaddr, ICMP6_RPL, RPL_CODE_DAO, pos);
    }
  }
  /*---------------------------------------------------------------------------*/
  static void
  dao_ack_input(void)
  {
  #if RPL_WITH_DAO_ACK
  
    uint8_t *buffer;
    uint8_t instance_id;
    uint8_t sequence;
    uint8_t status;
    rpl_instance_t *instance;
    rpl_parent_t *parent;
  
    buffer = UIP_ICMP_PAYLOAD;
  
    instance_id = buffer[0];
    sequence = buffer[2];
    status = buffer[3];
  
    instance = rpl_get_instance(instance_id);
    if(instance == NULL) {
      uipbuf_clear();
      return;
    }
  
    if(RPL_IS_STORING(instance)) {
      parent = rpl_find_parent(instance->current_dag, &UIP_IP_BUF->srcipaddr);
      if(parent == NULL) {
        /* not a known instance - drop the packet and ignore */
        uipbuf_clear();
        return;
      }
    } else {
      parent = NULL;
    }
  
    if(instance->current_dag->rank == ROOT_RANK(instance)) {
      LOG_DBG("DODAG root received a DAO ACK, ignoring it\n");
      uipbuf_clear();
      return;
    }
  
    LOG_INFO("Received a DAO %s with sequence number %d (%d) and status %d from ",
           status < 128 ? "ACK" : "NACK",
           sequence, instance->my_dao_seqno, status);
    LOG_INFO_6ADDR(&UIP_IP_BUF->srcipaddr);
    LOG_INFO_("\n");
  
    if(sequence == instance->my_dao_seqno) {
      instance->has_downward_route = status < 128;
  
      /* always stop the retransmit timer when the ACK arrived */
      ctimer_stop(&instance->dao_retransmit_timer);
  
      /* Inform objective function on status of the DAO ACK */
      if(RPL_IS_STORING(instance) && instance->of->dao_ack_callback) {
        instance->of->dao_ack_callback(parent, status);
      }
  
  #if RPL_REPAIR_ON_DAO_NACK
      if(status >= RPL_DAO_ACK_UNABLE_TO_ACCEPT) {
        /*
         * Failed the DAO transmission - need to remove the default route.
         * Trigger a local repair since we can not get our DAO in.
         */
        rpl_local_repair(instance);
      }
  #endif
  
    } else if(RPL_IS_STORING(instance)) {
      /* this DAO ACK should be forwarded to another recently registered route */
      uip_ds6_route_t *re;
      const uip_ipaddr_t *nexthop;
      if((re = find_route_entry_by_dao_ack(sequence)) != NULL) {
        /* pick the recorded seq no from that node and forward DAO ACK - and
           clear the pending flag*/
        RPL_ROUTE_CLEAR_DAO_PENDING(re);
  
        nexthop = uip_ds6_route_nexthop(re);
        if(nexthop == NULL) {
          LOG_WARN("No next hop to fwd DAO ACK to\n");
        } else {
          LOG_INFO("Fwd DAO ACK to:");
          LOG_INFO_6ADDR(nexthop);
          LOG_INFO_("\n");
          buffer[2] = re->state.dao_seqno_in;
          uip_icmp6_send(nexthop, ICMP6_RPL, RPL_CODE_DAO_ACK, 4);
        }
  
        if(status >= RPL_DAO_ACK_UNABLE_TO_ACCEPT) {
          /* this node did not get in to the routing tables above... - remove */
          uip_ds6_route_rm(re);
        }
      } else {
        LOG_WARN("No route entry found to forward DAO ACK (seqno %u)\n", sequence);
      }
    }
  #endif /* RPL_WITH_DAO_ACK */
    uipbuf_clear();
  }
  /*---------------------------------------------------------------------------*/
  void
  dao_ack_output(rpl_instance_t *instance, uip_ipaddr_t *dest, uint8_t sequence,
                 uint8_t status)
  {
  #if RPL_WITH_DAO_ACK
    unsigned char *buffer;
  
    LOG_INFO("Sending a DAO %s with sequence number %d to ", status < 128 ? "ACK" : "NACK", sequence);
    LOG_INFO_6ADDR(dest);
    LOG_INFO_(" with status %d\n", status);
  
    buffer = UIP_ICMP_PAYLOAD;
  
    buffer[0] = instance->instance_id;
    buffer[1] = 0;
    buffer[2] = sequence;
    buffer[3] = status;
  
    uip_icmp6_send(dest, ICMP6_RPL, RPL_CODE_DAO_ACK, 4);
  #endif /* RPL_WITH_DAO_ACK */
  }
  /*---------------------------------------------------------------------------*/
  void
  rpl_icmp6_register_handlers()
  {
    uip_icmp6_register_input_handler(&dis_handler);
    uip_icmp6_register_input_handler(&dio_handler);
    uip_icmp6_register_input_handler(&dao_handler);
    uip_icmp6_register_input_handler(&dao_ack_handler);
  }
  /*---------------------------------------------------------------------------*/
  
  /** @}*/
  