nes-proj/os/net/routing/rpl-classic/rpl-ext-header.c

/*
 * Copyright (c) 2009, 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
 *         Management of extension headers for ContikiRPL.
 *
 * \author Vincent Brillault <vincent.brillault@imag.fr>,
 *         Joakim Eriksson <joakime@sics.se>,
 *         Niclas Finne <nfi@sics.se>,
 *         Nicolas Tsiftes <nvt@sics.se>.
 */

/**
 * \addtogroup uip
 * @{
 */

#include "net/routing/routing.h"
#include "net/ipv6/uip.h"
#include "net/ipv6/tcpip.h"
#include "net/ipv6/uip-ds6.h"
#include "net/ipv6/uip-sr.h"
#include "net/routing/rpl-classic/rpl-private.h"
#include "net/packetbuf.h"

#include "sys/log.h"

#define LOG_MODULE "RPL"
#define LOG_LEVEL LOG_LEVEL_RPL

#include <limits.h>
#include <string.h>

/*---------------------------------------------------------------------------*/
int
rpl_ext_header_hbh_update(uint8_t *ext_buf, int opt_offset)
{
  rpl_instance_t *instance;
  int down;
  uint16_t sender_rank;
  uint8_t sender_closer;
  uip_ds6_route_t *route;
  rpl_parent_t *sender;
  struct uip_hbho_hdr *hbh_hdr = (struct uip_hbho_hdr *)ext_buf;
  struct uip_ext_hdr_opt_rpl *rpl_opt = (struct uip_ext_hdr_opt_rpl *)(ext_buf + opt_offset);

  if(hbh_hdr->len != ((RPL_HOP_BY_HOP_LEN - 8) / 8)
      || rpl_opt->opt_type != UIP_EXT_HDR_OPT_RPL
      || rpl_opt->opt_len != RPL_HDR_OPT_LEN) {

    LOG_ERR("Hop-by-hop extension header has wrong size or type (%u %u %u)\n",
        hbh_hdr->len, rpl_opt->opt_type, rpl_opt->opt_len);
    return 0; /* Drop */
  }

  instance = rpl_get_instance(rpl_opt->instance);
  if(instance == NULL) {
    LOG_ERR("Unknown instance: %u\n", rpl_opt->instance);
    return 0;
  }

  if(rpl_opt->flags & RPL_HDR_OPT_FWD_ERR) {
    LOG_ERR("Forward error!\n");
    /* We should try to repair it by removing the neighbor that caused
         the packet to be forwareded in the first place. We drop any
         routes that go through the neighbor that sent the packet to
         us. */
    if(RPL_IS_STORING(instance)) {
      route = uip_ds6_route_lookup(&UIP_IP_BUF->destipaddr);
      if(route != NULL) {
        uip_ds6_route_rm(route);
      }
    }
    RPL_STAT(rpl_stats.forward_errors++);
    /* Trigger DAO retransmission */
    rpl_reset_dio_timer(instance);
    /* drop the packet as it is not routable */
    return 0;
  }

  if(!instance->current_dag->joined) {
    LOG_ERR("No DAG in the instance\n");
    return 0;
  }
  down = 0;
  if(rpl_opt->flags & RPL_HDR_OPT_DOWN) {
    down = 1;
  }

  sender_rank = UIP_HTONS(rpl_opt->senderrank);
  sender = nbr_table_get_from_lladdr(rpl_parents, packetbuf_addr(PACKETBUF_ADDR_SENDER));

  if(sender != NULL && (rpl_opt->flags & RPL_HDR_OPT_RANK_ERR)) {
    /* A rank error was signalled, attempt to repair it by updating
     * the sender's rank from ext header */
    sender->rank = sender_rank;
    if(RPL_IS_NON_STORING(instance)) {
      /* Select DAG and preferred parent only in non-storing mode. In storing mode,
       * a parent switch would result in an immediate No-path DAO transmission, dropping
       * current incoming packet. */
      rpl_select_dag(instance, sender);
    }
  }

  sender_closer = sender_rank < instance->current_dag->rank;

  LOG_DBG("Packet going %s, sender closer %d (%d < %d)\n", down == 1 ? "down" : "up",
   sender_closer,
   sender_rank,
   instance->current_dag->rank
   );

  if((down && !sender_closer) || (!down && sender_closer)) {
    LOG_WARN("Loop detected - senderrank: %d my-rank: %d sender_closer: %d\n",
           sender_rank, instance->current_dag->rank,
           sender_closer);
    /* Attempt to repair the loop by sending a unicast DIO back to the sender
     * so that it gets a fresh update of our rank. */
    if(sender != NULL) {
      instance->unicast_dio_target = sender;
      rpl_schedule_unicast_dio_immediately(instance);
    }
    if(rpl_opt->flags & RPL_HDR_OPT_RANK_ERR) {
      RPL_STAT(rpl_stats.loop_errors++);
      LOG_ERR(" Rank error signalled in RPL option!\n");
      /* Packet must be dropped and dio trickle timer reset, see RFC6550 - 11.2.2.2 */
      rpl_reset_dio_timer(instance);
      return 0;
    }
    LOG_WARN("Single error tolerated\n");
    RPL_STAT(rpl_stats.loop_warnings++);
    rpl_opt->flags |= RPL_HDR_OPT_RANK_ERR;
    return 1;
  }

  LOG_DBG("Rank OK\n");
  return 1;
}
/*---------------------------------------------------------------------------*/
int
rpl_ext_header_srh_get_next_hop(uip_ipaddr_t *ipaddr)
{
#if RPL_WITH_NON_STORING
  struct uip_routing_hdr *rh_header;
  rpl_dag_t *dag;
  uip_sr_node_t *dest_node;
  uip_sr_node_t *root_node;

  /* Look for routing ext header */
  rh_header = (struct uip_routing_hdr *)uipbuf_search_header(uip_buf, uip_len, UIP_PROTO_ROUTING);

  dag = rpl_get_dag(&UIP_IP_BUF->destipaddr);
  root_node = uip_sr_get_node(dag, &dag->dag_id);
  dest_node = uip_sr_get_node(dag, &UIP_IP_BUF->destipaddr);

  if((rh_header != NULL && rh_header->routing_type == RPL_RH_TYPE_SRH) ||
     (dest_node != NULL && root_node != NULL &&
      dest_node->parent == root_node)) {
    /* Routing header found or the packet destined for a direct child of the root.
     * The next hop should be already copied as the IPv6 destination
     * address, via rpl_ext_header_srh_update. We turn this address into a link-local to enable
     * forwarding to next hop */
    uip_ipaddr_copy(ipaddr, &UIP_IP_BUF->destipaddr);
    uip_create_linklocal_prefix(ipaddr);
    return 1;
  }

  return 0;
#else /* RPL_WITH_NON_STORING */
  return 0; /* SRH not found */
#endif /* RPL_WITH_NON_STORING */
}
/*---------------------------------------------------------------------------*/
int
rpl_ext_header_srh_update(void)
{
#if RPL_WITH_NON_STORING
  struct uip_routing_hdr *rh_header;
  struct uip_rpl_srh_hdr *srh_header;

  /* Look for routing ext header */
  rh_header = (struct uip_routing_hdr *)uipbuf_search_header(uip_buf, uip_len, UIP_PROTO_ROUTING);

  if(rh_header != NULL && rh_header->routing_type == RPL_RH_TYPE_SRH) {
    /* SRH found, now look for next hop */
    uint8_t cmpri, cmpre;
    uint8_t ext_len;
    uint8_t padding;
    uint8_t path_len;
    uint8_t segments_left;
    uip_ipaddr_t current_dest_addr;

    srh_header = (struct uip_rpl_srh_hdr *)(((uint8_t *)rh_header) + RPL_RH_LEN);
    segments_left = rh_header->seg_left;
    ext_len = rh_header->len * 8 + 8;
    cmpri = srh_header->cmpr >> 4;
    cmpre = srh_header->cmpr & 0x0f;
    padding = srh_header->pad >> 4;
    path_len = ((ext_len - padding - RPL_RH_LEN - RPL_SRH_LEN - (16 - cmpre)) / (16 - cmpri)) + 1;
    (void)path_len;

    LOG_DBG("read SRH, path len %u, segments left %u, Cmpri %u, Cmpre %u, ext len %u (padding %u)\n",
        path_len, segments_left, cmpri, cmpre, ext_len, padding);

    if(segments_left == 0) {
      /* We are the final destination, do nothing */
    } else {
      uint8_t i = path_len - segments_left; /* The index of the next address to be visited */
      uint8_t *addr_ptr = ((uint8_t *)rh_header) + RPL_RH_LEN + RPL_SRH_LEN + (i * (16 - cmpri));
      uint8_t cmpr = segments_left == 1 ? cmpre : cmpri;

      /* As per RFC6554: swap the IPv6 destination address and address[i] */

      /* First, copy the current IPv6 destination address */
      uip_ipaddr_copy(&current_dest_addr, &UIP_IP_BUF->destipaddr);
      /* Second, update the IPv6 destination address with addresses[i] */
      memcpy(((uint8_t *)&UIP_IP_BUF->destipaddr) + cmpr, addr_ptr, 16 - cmpr);
      /* Third, write current_dest_addr to addresses[i] */
      memcpy(addr_ptr, ((uint8_t *)&current_dest_addr) + cmpr, 16 - cmpr);

      /* Update segments left field */
      rh_header->seg_left--;

      LOG_INFO("SRH next hop ");
      LOG_INFO_6ADDR(&UIP_IP_BUF->destipaddr);
      LOG_INFO_("\n");
    }
    return 1;
  }

  return 0;
#else /* RPL_WITH_NON_STORING */
  return 0; /* SRH not found */
#endif /* RPL_WITH_NON_STORING */
}
/*---------------------------------------------------------------------------*/
static int
count_matching_bytes(const void *p1, const void *p2, size_t n)
{
  int i = 0;
  for(i = 0; i < n; i++) {
    if(((uint8_t *)p1)[i] != ((uint8_t *)p2)[i]) {
      return i;
    }
  }
  return n;
}
/*---------------------------------------------------------------------------*/
static int
insert_srh_header(void)
{
  /* Implementation of RFC6554 */
  uint8_t path_len;
  uint8_t ext_len;
  uint8_t cmpri, cmpre; /* ComprI and ComprE fields of the RPL Source Routing Header */
  uint8_t *hop_ptr;
  uint8_t padding;
  uip_sr_node_t *dest_node;
  uip_sr_node_t *root_node;
  uip_sr_node_t *node;
  rpl_dag_t *dag;
  uip_ipaddr_t node_addr;

  /* Always insest SRH as first extension header */
  struct uip_routing_hdr *rh_hdr = (struct uip_routing_hdr *)UIP_IP_PAYLOAD(0);
  struct uip_rpl_srh_hdr *srh_hdr = (struct uip_rpl_srh_hdr *)(UIP_IP_PAYLOAD(0) + RPL_RH_LEN);

  LOG_INFO("SRH creating source routing header with destination ");
  LOG_INFO_6ADDR(&UIP_IP_BUF->destipaddr);
  LOG_INFO_("\n");

  /* Construct source route. We do not do this recursively to keep the runtime stack usage constant. */

  /* Get link of the destination and root */
  dag = rpl_get_dag(&UIP_IP_BUF->destipaddr);

  if(dag == NULL) {
    LOG_ERR("SRH DAG not found\n");
    return 0;
  }

  dest_node = uip_sr_get_node(dag, &UIP_IP_BUF->destipaddr);
  if(dest_node == NULL) {
    /* The destination is not found, skip SRH insertion */
    return 1;
  }

  root_node = uip_sr_get_node(dag, &dag->dag_id);
  if(root_node == NULL) {
    LOG_ERR("SRH root node not found\n");
    return 0;
  }

  if(!uip_sr_is_addr_reachable(dag, &UIP_IP_BUF->destipaddr)) {
    LOG_ERR("SRH no path found to destination\n");
    return 0;
  }

  /* Compute path length and compression factors (we use cmpri == cmpre) */
  path_len = 0;
  node = dest_node->parent;
  /* For simplicity, we use cmpri = cmpre */
  cmpri = 15;
  cmpre = 15;

  if(node == root_node) {
    LOG_DBG("SRH no need to insert SRH\n");
    return 1;
  }

  while(node != NULL && node != root_node) {

    NETSTACK_ROUTING.get_sr_node_ipaddr(&node_addr, node);

    /* How many bytes in common between all nodes in the path? */
    cmpri = MIN(cmpri, count_matching_bytes(&node_addr, &UIP_IP_BUF->destipaddr, 16));
    cmpre = cmpri;

    LOG_DBG("SRH Hop ");
    LOG_DBG_6ADDR(&node_addr);
    LOG_DBG_("\n");
    node = node->parent;
    path_len++;
  }

  /* Extension header length: fixed headers + (n-1) * (16-ComprI) + (16-ComprE)*/
  ext_len = RPL_RH_LEN + RPL_SRH_LEN
      + (path_len - 1) * (16 - cmpre)
      + (16 - cmpri);

  padding = ext_len % 8 == 0 ? 0 : (8 - (ext_len % 8));
  ext_len += padding;

  LOG_DBG("SRH Path len: %u, ComprI %u, ComprE %u, ext len %u (padding %u)\n",
      path_len, cmpri, cmpre, ext_len, padding);

  /* Check if there is enough space to store the extension header */
  if(uip_len + ext_len > UIP_LINK_MTU) {
    LOG_ERR("Packet too long: impossible to add source routing header (%u bytes)\n", ext_len);
    return 0;
  }

  /* Move existing ext headers and payload ext_len further */
  memmove(uip_buf + UIP_IPH_LEN + uip_ext_len + ext_len,
      uip_buf + UIP_IPH_LEN + uip_ext_len, uip_len - UIP_IPH_LEN);
  memset(uip_buf + UIP_IPH_LEN + uip_ext_len, 0, ext_len);

  /* Insert source routing header (as first ext header) */
  rh_hdr->next = UIP_IP_BUF->proto;
  UIP_IP_BUF->proto = UIP_PROTO_ROUTING;

  /* Initialize IPv6 Routing Header */
  rh_hdr->len = (ext_len - 8) / 8;
  rh_hdr->routing_type = RPL_RH_TYPE_SRH;
  rh_hdr->seg_left = path_len;

  /* Initialize RPL Source Routing Header */
  srh_hdr->cmpr = (cmpri << 4) + cmpre;
  srh_hdr->pad = padding << 4;

  /* Initialize addresses field (the actual source route).
   * From last to first. */
  node = dest_node;
  hop_ptr = ((uint8_t *)rh_hdr) + ext_len - padding; /* Pointer where to write the next hop compressed address */

  while(node != NULL && node->parent != root_node) {
    NETSTACK_ROUTING.get_sr_node_ipaddr(&node_addr, node);

    hop_ptr -= (16 - cmpri);
    memcpy(hop_ptr, ((uint8_t*)&node_addr) + cmpri, 16 - cmpri);

    node = node->parent;
  }

  /* The next hop (i.e. node whose parent is the root) is placed as the current IPv6 destination */
  NETSTACK_ROUTING.get_sr_node_ipaddr(&node_addr, node);
  uip_ipaddr_copy(&UIP_IP_BUF->destipaddr, &node_addr);

  /* Update the IPv6 length field */
  uipbuf_add_ext_hdr(ext_len);
  uipbuf_set_len_field(UIP_IP_BUF, uip_len - UIP_IPH_LEN);

  return 1;
}
/*---------------------------------------------------------------------------*/
static int
update_hbh_header(void)
{
  rpl_instance_t *instance;
  rpl_parent_t *parent;
  struct uip_hbho_hdr *hbh_hdr = (struct uip_hbho_hdr *)UIP_IP_PAYLOAD(0);
  struct uip_ext_hdr_opt_rpl *rpl_opt = (struct uip_ext_hdr_opt_rpl *)(UIP_IP_PAYLOAD(0) + 2);

  if(UIP_IP_BUF->proto == UIP_PROTO_HBHO && rpl_opt->opt_type == UIP_EXT_HDR_OPT_RPL) {
    if(hbh_hdr->len != ((RPL_HOP_BY_HOP_LEN - 8) / 8)
        || rpl_opt->opt_len != RPL_HDR_OPT_LEN) {

      LOG_ERR("Hop-by-hop extension header has wrong size (%u)\n", rpl_opt->opt_len);
      return 0; /* Drop */
    }

    instance = rpl_get_instance(rpl_opt->instance);
    if(instance == NULL || !instance->used || !instance->current_dag->joined) {
      LOG_ERR("Unable to add/update hop-by-hop extension header: incorrect instance\n");
      return 0; /* Drop */
    }

    LOG_INFO("Updating RPL option\n");
    /* Update sender rank and instance, will update flags next */
    rpl_opt->senderrank = UIP_HTONS(instance->current_dag->rank);
    rpl_opt->instance = instance->instance_id;

    if(RPL_IS_STORING(instance)) { /* In non-storing mode, downwards traffic does not have the HBH option */
      /* Check the direction of the down flag, as per Section 11.2.2.3,
            which states that if a packet is going down it should in
            general not go back up again. If this happens, a
            RPL_HDR_OPT_FWD_ERR should be flagged. */
      if((rpl_opt->flags & RPL_HDR_OPT_DOWN)) {
        if(uip_ds6_route_lookup(&UIP_IP_BUF->destipaddr) == NULL) {
          rpl_opt->flags |= RPL_HDR_OPT_FWD_ERR;
          LOG_WARN("RPL forwarding error\n");
          /* We should send back the packet to the originating parent,
                but it is not feasible yet, so we send a No-Path DAO instead */
          LOG_WARN("RPL generate No-Path DAO\n");
          parent = rpl_get_parent((uip_lladdr_t *)packetbuf_addr(PACKETBUF_ADDR_SENDER));
          if(parent != NULL) {
            dao_output_target(parent, &UIP_IP_BUF->destipaddr, RPL_ZERO_LIFETIME);
          }
          /* Drop packet */
          return 0;
        }
      } else {
        /* Set the down extension flag correctly as described in Section
              11.2 of RFC6550. If the packet progresses along a DAO route,
              the down flag should be set. */
        if(uip_ds6_route_lookup(&UIP_IP_BUF->destipaddr) == NULL) {
          /* No route was found, so this packet will go towards the RPL
                root. If so, we should not set the down flag. */
          rpl_opt->flags &= ~RPL_HDR_OPT_DOWN;
          LOG_DBG("RPL option going up\n");
        } else {
          /* A DAO route was found so we set the down flag. */
          rpl_opt->flags |= RPL_HDR_OPT_DOWN;
          LOG_DBG("RPL option going down\n");
        }
      }
    }
  }

  return 1;
}
/*---------------------------------------------------------------------------*/
static int
insert_hbh_header(const rpl_instance_t *instance)
{
  struct uip_hbho_hdr *hbh_hdr = (struct uip_hbho_hdr *)UIP_IP_PAYLOAD(0);
  struct uip_ext_hdr_opt_rpl *rpl_opt = (struct uip_ext_hdr_opt_rpl *)(UIP_IP_PAYLOAD(2));

  /* Insert hop-by-hop header */
  LOG_DBG("Creating hop-by-hop option\n");
  if(uip_len + RPL_HOP_BY_HOP_LEN > UIP_LINK_MTU) {
    LOG_ERR("Packet too long: impossible to add hop-by-hop option\n");
    return 0;
  }

  /* Move existing ext headers and payload RPL_HOP_BY_HOP_LEN further */
  memmove(UIP_IP_PAYLOAD(RPL_HOP_BY_HOP_LEN), UIP_IP_PAYLOAD(0), uip_len - UIP_IPH_LEN);
  memset(UIP_IP_PAYLOAD(0), 0, RPL_HOP_BY_HOP_LEN);

  /* Insert HBH header (as first ext header) */
  hbh_hdr->next = UIP_IP_BUF->proto;
  UIP_IP_BUF->proto = UIP_PROTO_HBHO;

  /* Initialize HBH option */
  hbh_hdr->len = (RPL_HOP_BY_HOP_LEN - 8) / 8;
  rpl_opt->opt_type = UIP_EXT_HDR_OPT_RPL;
  rpl_opt->opt_len = RPL_HDR_OPT_LEN;
  rpl_opt->flags = 0;
  rpl_opt->senderrank = UIP_HTONS(instance->current_dag->rank);
  rpl_opt->instance = instance->instance_id;

  uipbuf_add_ext_hdr(RPL_HOP_BY_HOP_LEN);
  uipbuf_set_len_field(UIP_IP_BUF, uip_len - UIP_IPH_LEN);

  /* Update header before returning */
  return update_hbh_header();
}
/*---------------------------------------------------------------------------*/
void
rpl_ext_header_remove(void)
{
  uint8_t *prev_proto_ptr;
  uint8_t protocol;
  uint8_t ext_len;
  uint8_t *next_header;
  struct uip_ext_hdr *ext_ptr;
  struct uip_ext_hdr_opt *opt_ptr;

  next_header = uipbuf_get_next_header(uip_buf, uip_len, &protocol, true);
  ext_ptr = (struct uip_ext_hdr *)next_header;
  prev_proto_ptr = &UIP_IP_BUF->proto;
  while(next_header != NULL && uip_is_proto_ext_hdr(protocol)) {
    opt_ptr = (struct uip_ext_hdr_opt *)(next_header + 2);
    if(protocol == UIP_PROTO_ROUTING || (protocol == UIP_PROTO_HBHO && opt_ptr->type == UIP_EXT_HDR_OPT_RPL)) {
      /* Remove ext header */
      *prev_proto_ptr = ext_ptr->next;
      ext_len = ext_ptr->len * 8 + 8;
      uipbuf_add_ext_hdr(-ext_len);
      /* Update length field and rest of packer to the "left" */
      uipbuf_set_len_field(UIP_IP_BUF, uip_len - UIP_IPH_LEN);
      memmove(next_header, next_header + ext_len, uip_len - (next_header - uip_buf));
      /* Update loop variables */
      protocol = *prev_proto_ptr;
    } else {
      /* move to the ext hdr */
      next_header = uipbuf_get_next_header(next_header, uip_len - (next_header - uip_buf), &protocol, false);
      ext_ptr = (struct uip_ext_hdr *)next_header;
      prev_proto_ptr = &ext_ptr->next;
    }
  }
}
/*---------------------------------------------------------------------------*/
int
rpl_ext_header_update(void)
{
  if(default_instance == NULL || default_instance->current_dag == NULL
      || uip_is_addr_linklocal(&UIP_IP_BUF->destipaddr) || uip_is_addr_mcast(&UIP_IP_BUF->destipaddr)) {
    return 1;
  }

  if(default_instance->current_dag->rank == ROOT_RANK(default_instance)) {
    /* At the root, remove headers if any, and insert SRH or HBH
    * (SRH is inserted only if the destination is in the DODAG) */
    rpl_ext_header_remove();
    if(rpl_get_dag(&UIP_IP_BUF->destipaddr) != NULL) {
      /* dest is in a DODAG; the packet is going down. */
      if(RPL_IS_NON_STORING(default_instance)) {
        return insert_srh_header();
      } else {
        return insert_hbh_header(default_instance);
      }
    } else {
      /* dest is outside of DODAGs; no ext header is needed. */
      return 1;
    }
  } else {
    if(uip_ds6_is_my_addr(&UIP_IP_BUF->srcipaddr)
        && UIP_IP_BUF->ttl == uip_ds6_if.cur_hop_limit) {
      /* Insert HBH option at source. Checking the address is not sufficient because
       * in non-storing mode, a packet may go up and then down the same path again */
      return insert_hbh_header(default_instance);
    } else {
      /* Update HBH option at forwarders */
      return update_hbh_header();
    }
  }
}

/** @}*/