--- F:\nd6_new.c	Wed Aug 27 11:50:22 2014
+++ F:\nd6.c	Tue Sep  2 03:35:10 2014
@@ -1,1843 +1,1793 @@
-/**
- * @file
- *
- * Neighbor discovery and stateless address autoconfiguration for IPv6.
- * Aims to be compliant with RFC 4861 (Neighbor discovery) and RFC 4862
- * (Address autoconfiguration).
- */
-
-/*
- * Copyright (c) 2010 Inico Technologies Ltd.
- * 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. The name of the author may not be used to endorse or promote products
- *    derived from this software without specific prior written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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 lwIP TCP/IP stack.
- *
- * Author: Ivan Delamer <delamer@inicotech.com>
- *
- *
- * Please coordinate changes and requests with Ivan Delamer
- * <delamer@inicotech.com>
- */
-
-#include "lwip/opt.h"
-
-#if LWIP_IPV6  /* don't build if not configured for use in lwipopts.h */
-
-#include "lwip/nd6.h"
-#include "lwip/pbuf.h"
-#include "lwip/mem.h"
-#include "lwip/memp.h"
-#include "lwip/ip6.h"
-#include "lwip/ip6_addr.h"
-#include "lwip/inet_chksum.h"
-#include "lwip/netif.h"
-#include "lwip/icmp6.h"
-#include "lwip/mld6.h"
-#include "lwip/ip.h"
-#include "lwip/stats.h"
-
-#include <string.h>
-
-
-/* Router tables. */
-struct nd6_neighbor_cache_entry neighbor_cache[LWIP_ND6_NUM_NEIGHBORS];
-struct nd6_destination_cache_entry destination_cache[LWIP_ND6_NUM_DESTINATIONS];
-struct nd6_prefix_list_entry prefix_list[LWIP_ND6_NUM_PREFIXES];
-struct nd6_router_list_entry default_router_list[LWIP_ND6_NUM_ROUTERS];
-
-/* Default values, can be updated by a RA message. */
-u32_t reachable_time = LWIP_ND6_REACHABLE_TIME;
-u32_t retrans_timer = LWIP_ND6_RETRANS_TIMER; /* TODO implement this value in timer */
-
-/* Index for cache entries. */
-static u8_t nd6_cached_neighbor_index;
-static u8_t nd6_cached_destination_index;
-
-/* Multicast address holder. */
-static ip6_addr_t multicast_address;
-
-/* Static buffer to parse RA packet options (size of a prefix option, biggest option) */
-static u8_t nd6_ra_buffer[sizeof(struct prefix_option)];
-
-/* Forward declarations. */
-static s8_t nd6_find_neighbor_cache_entry(ip6_addr_t * ip6addr);
-static s8_t nd6_new_neighbor_cache_entry(void);
-static void nd6_free_neighbor_cache_entry(s8_t i);
-static s8_t nd6_find_destination_cache_entry(ip6_addr_t * ip6addr);
-static s8_t nd6_new_destination_cache_entry(void);
-static s8_t nd6_is_prefix_in_netif(ip6_addr_t * ip6addr, struct netif * netif);
-static s8_t nd6_get_router(ip6_addr_t * router_addr, struct netif * netif);
-static s8_t nd6_new_router(ip6_addr_t * router_addr, struct netif * netif);
-static s8_t nd6_get_onlink_prefix(ip6_addr_t * prefix, struct netif * netif);
-static s8_t nd6_new_onlink_prefix(ip6_addr_t * prefix, struct netif * netif);

-
-#define ND6_SEND_FLAG_MULTICAST_DEST 0x01
-#define ND6_SEND_FLAG_ALLNODES_DEST 0x02
-static void nd6_send_ns(struct netif * netif, ip6_addr_t * target_addr, u8_t flags);
-static void nd6_send_na(struct netif * netif, ip6_addr_t * target_addr, u8_t flags);
-#if LWIP_IPV6_SEND_ROUTER_SOLICIT
-static void nd6_send_rs(struct netif * netif);
-#endif /* LWIP_IPV6_SEND_ROUTER_SOLICIT */
-
-#if LWIP_ND6_QUEUEING
-static void nd6_free_q(struct nd6_q_entry *q);
-#else /* LWIP_ND6_QUEUEING */
-#define nd6_free_q(q) pbuf_free(q)
-#endif /* LWIP_ND6_QUEUEING */
-static void nd6_send_q(s8_t i);
-
-
-/**
- * Process an incoming neighbor discovery message
- *
- * @param p the nd packet, p->payload pointing to the icmpv6 header
- * @param inp the netif on which this packet was received
- */
-void
-nd6_input(struct pbuf *p, struct netif *inp)
-{
-  u8_t msg_type;
-  s8_t i;
-
-  ND6_STATS_INC(nd6.recv);
-
-  msg_type = *((u8_t *)p->payload);
-  switch (msg_type) {
-  case ICMP6_TYPE_NA: /* Neighbor Advertisement. */
-  {
-    struct na_header * na_hdr;
-    struct lladdr_option * lladdr_opt;
-
-    /* Check that na header fits in packet. */
-    if (p->len < (sizeof(struct na_header))) {
-      /* TODO debug message */
-      pbuf_free(p);
-      ND6_STATS_INC(nd6.lenerr);
-      ND6_STATS_INC(nd6.drop);
-      return;
-    }
-
-    na_hdr = (struct na_header *)p->payload;
-
-    /* Unsolicited NA?*/
-    if (ip6_addr_ismulticast(ip6_current_dest_addr())) {
-      /* This is an unsolicited NA.
-       * link-layer changed?
-       * part of DAD mechanism? */
-
-      /* Check that link-layer address option also fits in packet. */
-      lladdr_opt = (struct lladdr_option *)((u8_t*)p->payload + sizeof(struct na_header));
-      if (p->len < (sizeof(struct na_header) + (lladdr_opt->length << 3))) {
-        /* TODO debug message */
-        pbuf_free(p);
-        ND6_STATS_INC(nd6.lenerr);
-        ND6_STATS_INC(nd6.drop);
-        return;
-      }
-
-      /* Override ip6_current_dest_addr() so that we have an aligned copy. */
-      ip6_addr_set(ip6_current_dest_addr(), &(na_hdr->target_address));
-
-#if LWIP_IPV6_DUP_DETECT_ATTEMPTS
-      /* If the target address matches this netif, it is a DAD response. */
-      for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; i++) {
-        if (ip6_addr_cmp(ip6_current_dest_addr(), netif_ip6_addr(inp, i))) {
-          /* We are using a duplicate address. */
-          netif_ip6_addr_set_state(inp, i, IP6_ADDR_INVALID);
-
-#if LWIP_IPV6_MLD
-          /* Leave solicited node multicast group. */
-          ip6_addr_set_solicitednode(&multicast_address, netif_ip6_addr(inp, i)->addr[3]);
-          mld6_leavegroup(netif_ip6_addr(inp, i), &multicast_address);
-#endif /* LWIP_IPV6_MLD */
-
-
-
-
-#if LWIP_IPV6_AUTOCONFIG
-          /* Check to see if this address was autoconfigured. */
-          if (!ip6_addr_islinklocal(ip6_current_dest_addr())) {
-            i = nd6_get_onlink_prefix(ip6_current_dest_addr(), inp);

-            if (i >= 0) {
-              /* Mark this prefix as duplicate, so that we don't use it
-               * to generate this address again. */
-              prefix_list[i].flags |= ND6_PREFIX_AUTOCONFIG_ADDRESS_DUPLICATE;
-            }
-          }
-#endif /* LWIP_IPV6_AUTOCONFIG */
-
-          pbuf_free(p);
-          return;
-        }
-      }
-#endif /* LWIP_IPV6_DUP_DETECT_ATTEMPTS */
-
-      /* This is an unsolicited NA, most likely there was a LLADDR change. */
-      i = nd6_find_neighbor_cache_entry(ip6_current_dest_addr());
-      if (i >= 0) {
-        if (na_hdr->flags & ND6_FLAG_OVERRIDE) {
-          MEMCPY(neighbor_cache[i].lladdr, lladdr_opt->addr, inp->hwaddr_len);
-        }
-      }
-    }
-    else {
-      /* This is a solicited NA.
-       * neighbor address resolution response?
-       * neighbor unreachability detection response? */
-
-      /* Override ip6_current_dest_addr() so that we have an aligned copy. */
-      ip6_addr_set(ip6_current_dest_addr(), &(na_hdr->target_address));
-
-      /* Find the cache entry corresponding to this na. */
-      i = nd6_find_neighbor_cache_entry(ip6_current_dest_addr());
-      if (i < 0) {
-        /* We no longer care about this target address. drop it. */
-        pbuf_free(p);
-        return;
-      }
-
-      /* Update cache entry. */
-      neighbor_cache[i].netif = inp;
-      neighbor_cache[i].counter.reachable_time = reachable_time;
-      if ((na_hdr->flags & ND6_FLAG_OVERRIDE) ||
-          (neighbor_cache[i].state == ND6_INCOMPLETE)) {
-        /* Check that link-layer address option also fits in packet. */
-        lladdr_opt = (struct lladdr_option *)((u8_t*)p->payload + sizeof(struct na_header));
-        if (p->len < (sizeof(struct na_header) + (lladdr_opt->length << 3))) {
-          /* TODO debug message */
-          pbuf_free(p);
-          ND6_STATS_INC(nd6.lenerr);
-          ND6_STATS_INC(nd6.drop);
-          return;
-        }
-
-        lladdr_opt = (struct lladdr_option *)((u8_t*)p->payload + sizeof(struct na_header));
-
-        MEMCPY(neighbor_cache[i].lladdr, lladdr_opt->addr, inp->hwaddr_len);
-      }
-      neighbor_cache[i].state = ND6_REACHABLE;
-
-      /* Send queued packets, if any. */
-      if (neighbor_cache[i].q != NULL) {
-        nd6_send_q(i);
-      }
-    }
-
-    break; /* ICMP6_TYPE_NA */
-  }
-  case ICMP6_TYPE_NS: /* Neighbor solicitation. */
-  {
-    struct ns_header * ns_hdr;
-    struct lladdr_option * lladdr_opt;
-    u8_t accepted;
-
-    /* Check that ns header fits in packet. */
-    if (p->len < sizeof(struct ns_header)) {
-      /* TODO debug message */
-      pbuf_free(p);
-      ND6_STATS_INC(nd6.lenerr);
-      ND6_STATS_INC(nd6.drop);
-      return;
-    }
-
-    ns_hdr = (struct ns_header *)p->payload;
-
-    /* Check if there is a link-layer address provided. Only point to it if in this buffer. */
-    lladdr_opt = (struct lladdr_option *)((u8_t*)p->payload + sizeof(struct ns_header));
-    if (p->len >= (sizeof(struct ns_header) + (lladdr_opt->length >> 3))) {
-      lladdr_opt = (struct lladdr_option *)((u8_t*)p->payload + sizeof(struct ns_header));
-    } else {
-      lladdr_opt = NULL;
-    }
-    /* Check if the target address is configured on the receiving netif. */
-    accepted = 0;
-    for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; ++i) {
-      if ((ip6_addr_isvalid(netif_ip6_addr_state(inp, i)) ||
-           (ip6_addr_istentative(netif_ip6_addr_state(inp, i)) &&
-            ip6_addr_isany(ip6_current_src_addr()))) &&
-          ip6_addr_cmp(&(ns_hdr->target_address), netif_ip6_addr(inp, i))) {
-        accepted = 1;
-        break;
-      }
-    }
-
-    /* NS not for us? */
-    if (!accepted) {
-      pbuf_free(p);
-      return;
-    }
-
-    /* Check for ANY address in src (DAD algorithm). */
-    if (ip6_addr_isany(ip6_current_src_addr())) {
-      /* Sender is validating this address. */
-      for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; ++i) {
-        if (ip6_addr_cmp(&(ns_hdr->target_address), netif_ip6_addr(inp, i))) {
-          /* Send a NA back so that the sender does not use this address. */
-          nd6_send_na(inp, netif_ip6_addr(inp, i), ND6_FLAG_OVERRIDE | ND6_SEND_FLAG_ALLNODES_DEST);
-          if (ip6_addr_istentative(netif_ip6_addr_state(inp, i))) {
-            /* We shouldn't use this address either. */
-            netif_ip6_addr_set_state(inp, i, IP6_ADDR_INVALID);
-          }
-        }
-      }
-    }
-    else {
-      /* Sender is trying to resolve our address. */
-      /* Verify that they included their own link-layer address. */
-      if (lladdr_opt == NULL) {
-        /* Not a valid message. */
-        pbuf_free(p);
-        ND6_STATS_INC(nd6.proterr);
-        ND6_STATS_INC(nd6.drop);
-        return;
-      }
-
-      i = nd6_find_neighbor_cache_entry(ip6_current_src_addr());
-      if ( i>= 0) {
-        /* We already have a record for the solicitor. */
-        if (neighbor_cache[i].state == ND6_INCOMPLETE) {
-          neighbor_cache[i].netif = inp;
-          MEMCPY(neighbor_cache[i].lladdr, lladdr_opt->addr, inp->hwaddr_len);
-
-          /* Delay probe in case we get confirmation of reachability from upper layer (TCP). */
-          neighbor_cache[i].state = ND6_DELAY;
-          neighbor_cache[i].counter.delay_time = LWIP_ND6_DELAY_FIRST_PROBE_TIME;
-        }
-      }
-      else
-      {
-        /* Add their IPv6 address and link-layer address to neighbor cache.
-         * We will need it at least to send a unicast NA message, but most
-         * likely we will also be communicating with this node soon. */
-        i = nd6_new_neighbor_cache_entry();
-        if (i < 0) {
-          /* We couldn't assign a cache entry for this neighbor.
-           * we won't be able to reply. drop it. */
-          pbuf_free(p);
-          ND6_STATS_INC(nd6.memerr);
-          return;
-        }
-        neighbor_cache[i].netif = inp;
-        MEMCPY(neighbor_cache[i].lladdr, lladdr_opt->addr, inp->hwaddr_len);
-        ip6_addr_set(&(neighbor_cache[i].next_hop_address), ip6_current_src_addr());
-
-        /* Receiving a message does not prove reachability: only in one direction.
-         * Delay probe in case we get confirmation of reachability from upper layer (TCP). */
-        neighbor_cache[i].state = ND6_DELAY;
-        neighbor_cache[i].counter.delay_time = LWIP_ND6_DELAY_FIRST_PROBE_TIME;
-      }
-
-      /* Override ip6_current_dest_addr() so that we have an aligned copy. */
-      ip6_addr_set(ip6_current_dest_addr(), &(ns_hdr->target_address));
-
-      /* Send back a NA for us. Allocate the reply pbuf. */
-      nd6_send_na(inp, ip6_current_dest_addr(), ND6_FLAG_SOLICITED | ND6_FLAG_OVERRIDE);
-    }
-
-    break; /* ICMP6_TYPE_NS */
-  }
-  case ICMP6_TYPE_RA: /* Router Advertisement. */
-  {
-    struct ra_header * ra_hdr;
-    u8_t * buffer;   /* Used to copy options. */
-    u16_t offset;
-
-    /* Check that RA header fits in packet. */
-    if (p->len < sizeof(struct ra_header)) {
-      /* TODO debug message */
-      pbuf_free(p);
-      ND6_STATS_INC(nd6.lenerr);
-      ND6_STATS_INC(nd6.drop);
-      return;
-    }
-
-    ra_hdr = (struct ra_header *)p->payload;
-
-    /* If we are sending RS messages, stop. */
-#if LWIP_IPV6_SEND_ROUTER_SOLICIT
-    inp->rs_count = 0;
-#endif /* LWIP_IPV6_SEND_ROUTER_SOLICIT */
-
-    /* Get the matching default router entry. */
-    i = nd6_get_router(ip6_current_src_addr(), inp);
-    if (i < 0) {
-      /* Create a new router entry. */
-      i = nd6_new_router(ip6_current_src_addr(), inp);
-    }
-
-    if (i < 0) {
-      /* Could not create a new router entry. */
-      pbuf_free(p);
-      ND6_STATS_INC(nd6.memerr);
-      return;
-    }
-
-    /* Re-set invalidation timer. */
-    default_router_list[i].invalidation_timer = ra_hdr->router_lifetime;
-
-    /* Re-set default timer values. */
-#if LWIP_ND6_ALLOW_RA_UPDATES
-    if (ra_hdr->retrans_timer > 0) {
-      retrans_timer = ra_hdr->retrans_timer;
-    }
-    if (ra_hdr->reachable_time > 0) {
-      reachable_time = ra_hdr->reachable_time;
-    }
-#endif /* LWIP_ND6_ALLOW_RA_UPDATES */
-
-    /* TODO set default hop limit... */
-    /* ra_hdr->current_hop_limit;*/
-
-    /* Update flags in local entry (incl. preference). */
-    default_router_list[i].flags = ra_hdr->flags;
-
-    /* Offset to options. */
-    offset = sizeof(struct ra_header);
-
-    /* Process each option. */
-    while ((p->tot_len - offset) > 0) {
-      if (p->len == p->tot_len) {
-        /* no need to copy from contiguous pbuf */
-        buffer = &((u8_t*)p->payload)[offset];
-      } else {
-        buffer = nd6_ra_buffer;
-        pbuf_copy_partial(p, buffer, sizeof(struct prefix_option), offset);
-      }
-      switch (buffer[0]) {
-      case ND6_OPTION_TYPE_SOURCE_LLADDR:
-      {
-        struct lladdr_option * lladdr_opt;
-        lladdr_opt = (struct lladdr_option *)buffer;
-        if ((default_router_list[i].neighbor_entry != NULL) &&
-            (default_router_list[i].neighbor_entry->state == ND6_INCOMPLETE)) {
-          SMEMCPY(default_router_list[i].neighbor_entry->lladdr, lladdr_opt->addr, inp->hwaddr_len);
-          default_router_list[i].neighbor_entry->state = ND6_REACHABLE;
-          default_router_list[i].neighbor_entry->counter.reachable_time = reachable_time;
-        }
-        break;
-      }
-      case ND6_OPTION_TYPE_MTU:
-      {
-        struct mtu_option * mtu_opt;
-        mtu_opt = (struct mtu_option *)buffer;
-        if (mtu_opt->mtu >= 1280) {
-#if LWIP_ND6_ALLOW_RA_UPDATES
-          inp->mtu = mtu_opt->mtu;
-#endif /* LWIP_ND6_ALLOW_RA_UPDATES */
-        }
-        break;
-      }
-      case ND6_OPTION_TYPE_PREFIX_INFO:
-      {
-        struct prefix_option * prefix_opt;
-        prefix_opt = (struct prefix_option *)buffer;
-
-        if (prefix_opt->flags & ND6_PREFIX_FLAG_ON_LINK) {
-          /* Add to on-link prefix list. */
-
-          /* Get a memory-aligned copy of the prefix. */
-          ip6_addr_set(ip6_current_dest_addr(), &(prefix_opt->prefix));
-
-          /* find cache entry for this prefix. */
-          i = nd6_get_onlink_prefix(ip6_current_dest_addr(), inp);
-          if (i < 0) {
-            /* Create a new cache entry. */
-            i = nd6_new_onlink_prefix(ip6_current_dest_addr(), inp);
-          }
-          if (i >= 0) {
-            prefix_list[i].invalidation_timer = prefix_opt->valid_lifetime;
-
-#if LWIP_IPV6_AUTOCONFIG
-            if (prefix_opt->flags & ND6_PREFIX_FLAG_AUTONOMOUS) {
-              /* Mark prefix as autonomous, so that address autoconfiguration can take place.
-               * Only OR flag, so that we don't over-write other flags (such as ADDRESS_DUPLICATE)*/
-              prefix_list[i].flags |= ND6_PREFIX_AUTOCONFIG_AUTONOMOUS;
-            }
-#endif /* LWIP_IPV6_AUTOCONFIG */
-          }
-        }
-
-        break;
-      }
-      case ND6_OPTION_TYPE_ROUTE_INFO:
-      {
-        /* TODO implement preferred routes.
-        struct route_option * route_opt;
-        route_opt = (struct route_option *)buffer;*/
-
-        break;
-      }
-      default:
-        /* Unrecognized option, abort. */
-        ND6_STATS_INC(nd6.proterr);
-        break;
-      }
-      offset += 8 * ((u16_t)buffer[1]);
-    }
-
-    break; /* ICMP6_TYPE_RA */
-  }
-  case ICMP6_TYPE_RD: /* Redirect */
-  {
-    struct redirect_header * redir_hdr;
-    struct lladdr_option * lladdr_opt;
-
-    /* Check that Redir header fits in packet. */
-    if (p->len < sizeof(struct redirect_header)) {
-      /* TODO debug message */
-      pbuf_free(p);
-      ND6_STATS_INC(nd6.lenerr);
-      ND6_STATS_INC(nd6.drop);
-      return;
-    }
-
-    redir_hdr = (struct redirect_header *)p->payload;
-
-    lladdr_opt = (struct lladdr_option *)((u8_t*)p->payload + sizeof(struct redirect_header));
-    if (p->len >= (sizeof(struct redirect_header) + (lladdr_opt->length << 3))) {

-      lladdr_opt = (struct lladdr_option *)((u8_t*)p->payload + sizeof(struct redirect_header));
-    } else {
-      lladdr_opt = NULL;
-    }
-
-    /* Copy original destination address to current source address, to have an aligned copy. */
-    ip6_addr_set(ip6_current_src_addr(), &(redir_hdr->destination_address));
-
-    /* Find dest address in cache */
-    i = nd6_find_destination_cache_entry(ip6_current_src_addr());
-    if (i < 0) {
-      /* Destination not in cache, drop packet. */
-      pbuf_free(p);
-      return;
-    }
-
-    /* Set the new target address. */
-    ip6_addr_set(&(destination_cache[i].next_hop_addr), &(redir_hdr->target_address));
-
-    /* If Link-layer address of other router is given, try to add to neighbor cache. */
-    if (lladdr_opt != NULL) {
-      if (lladdr_opt->type == ND6_OPTION_TYPE_TARGET_LLADDR) {
-        /* Copy target address to current source address, to have an aligned copy. */
-        ip6_addr_set(ip6_current_src_addr(), &(redir_hdr->target_address));
-
-        i = nd6_find_neighbor_cache_entry(ip6_current_src_addr());
-        if (i < 0) {
-          i = nd6_new_neighbor_cache_entry();
-          if (i >= 0) {
-            neighbor_cache[i].netif = inp;
-            MEMCPY(neighbor_cache[i].lladdr, lladdr_opt->addr, inp->hwaddr_len);
-            ip6_addr_set(&(neighbor_cache[i].next_hop_address), ip6_current_src_addr());
-
-            /* Receiving a message does not prove reachability: only in one direction.
-             * Delay probe in case we get confirmation of reachability from upper layer (TCP). */
-            neighbor_cache[i].state = ND6_DELAY;
-            neighbor_cache[i].counter.delay_time = LWIP_ND6_DELAY_FIRST_PROBE_TIME;
-          }
-        }
-        if (i >= 0) {
-          if (neighbor_cache[i].state == ND6_INCOMPLETE) {
-            MEMCPY(neighbor_cache[i].lladdr, lladdr_opt->addr, inp->hwaddr_len);
-            /* Receiving a message does not prove reachability: only in one direction.
-             * Delay probe in case we get confirmation of reachability from upper layer (TCP). */
-            neighbor_cache[i].state = ND6_DELAY;
-            neighbor_cache[i].counter.delay_time = LWIP_ND6_DELAY_FIRST_PROBE_TIME;
-          }
-        }
-      }
-    }
-    break; /* ICMP6_TYPE_RD */
-  }
-  case ICMP6_TYPE_PTB: /* Packet too big */
-  {
-    struct icmp6_hdr *icmp6hdr; /* Packet too big message */
-    struct ip6_hdr * ip6hdr; /* IPv6 header of the packet which caused the error */
-
-    /* Check that ICMPv6 header + IPv6 header fit in payload */
-    if (p->len < (sizeof(struct icmp6_hdr) + IP6_HLEN)) {
-      /* drop short packets */
-      pbuf_free(p);
-      ND6_STATS_INC(nd6.lenerr);
-      ND6_STATS_INC(nd6.drop);
-      return;
-    }
-
-    icmp6hdr = (struct icmp6_hdr *)p->payload;
-    ip6hdr = (struct ip6_hdr *)((u8_t*)p->payload + sizeof(struct icmp6_hdr));
-
-    /* Copy original destination address to current source address, to have an aligned copy. */
-    ip6_addr_set(ip6_current_src_addr(), &(ip6hdr->dest));
-
-    /* Look for entry in destination cache. */
-    i = nd6_find_destination_cache_entry(ip6_current_src_addr());
-    if (i < 0) {
-      /* Destination not in cache, drop packet. */
-      pbuf_free(p);
-      return;
-    }
-
-    /* Change the Path MTU. */
-    destination_cache[i].pmtu = icmp6hdr->data;
-
-    break; /* ICMP6_TYPE_PTB */
-  }
-
-  default:
-    ND6_STATS_INC(nd6.proterr);
-    ND6_STATS_INC(nd6.drop);
-    break; /* default */
-  }
-
-  pbuf_free(p);
-}
-
-
-/**
- * Periodic timer for Neighbor discovery functions:
- *
- * - Update neighbor reachability states
- * - Update destination cache entries age
- * - Update invalidation timers of default routers and on-link prefixes
- * - Perform duplicate address detection (DAD) for our addresses
- * - Send router solicitations
- */
-void
-nd6_tmr(void)
-{
-  s8_t i, j;
-  struct netif * netif;
-
-  /* Process neighbor entries. */
-  for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++) {
-    switch (neighbor_cache[i].state) {
-    case ND6_INCOMPLETE:
-      if (neighbor_cache[i].counter.probes_sent >= LWIP_ND6_MAX_MULTICAST_SOLICIT) {
-        /* Retries exceeded. */
-        nd6_free_neighbor_cache_entry(i);
-      }
-      else {
-        /* Send a NS for this entry. */
-        neighbor_cache[i].counter.probes_sent++;
-        nd6_send_ns(neighbor_cache[i].netif, &(neighbor_cache[i].next_hop_address), ND6_SEND_FLAG_MULTICAST_DEST);
-      }
-      break;
-    case ND6_REACHABLE:
-      /* Send queued packets, if any are left. Should have been sent already. */
-      if (neighbor_cache[i].q != NULL) {
-        nd6_send_q(i);
-      }
-      if (neighbor_cache[i].counter.reachable_time <= ND6_TMR_INTERVAL) {
-        /* Change to stale state. */
-        neighbor_cache[i].state = ND6_STALE;
-        neighbor_cache[i].counter.stale_time = 0;
-      }
-      else {
-        neighbor_cache[i].counter.reachable_time -= ND6_TMR_INTERVAL;
-      }
-      break;
-    case ND6_STALE:
-      neighbor_cache[i].counter.stale_time += ND6_TMR_INTERVAL;
-      break;
-    case ND6_DELAY:
-      if (neighbor_cache[i].counter.delay_time <= ND6_TMR_INTERVAL) {
-        /* Change to PROBE state. */
-        neighbor_cache[i].state = ND6_PROBE;
-        neighbor_cache[i].counter.probes_sent = 0;
-      }
-      else {
-        neighbor_cache[i].counter.delay_time -= ND6_TMR_INTERVAL;
-      }
-      break;
-    case ND6_PROBE:
-      if (neighbor_cache[i].counter.probes_sent >= LWIP_ND6_MAX_MULTICAST_SOLICIT) {
-        /* Retries exceeded. */
-        nd6_free_neighbor_cache_entry(i);
-      }
-      else {
-        /* Send a NS for this entry. */
-        neighbor_cache[i].counter.probes_sent++;
-        nd6_send_ns(neighbor_cache[i].netif, &(neighbor_cache[i].next_hop_address), 0);
-      }
-      break;
-    case ND6_NO_ENTRY:
-    default:
-      /* Do nothing. */
-      break;
-    }
-  }
-
-  /* Process destination entries. */
-  for (i = 0; i < LWIP_ND6_NUM_DESTINATIONS; i++) {
-    destination_cache[i].age++;
-  }
-
-  /* Process router entries. */
-  for (i = 0; i < LWIP_ND6_NUM_ROUTERS; i++) {
-    if (default_router_list[i].neighbor_entry != NULL) {
-      /* Active entry. */
-      if (default_router_list[i].invalidation_timer > 0) {
-        default_router_list[i].invalidation_timer -= ND6_TMR_INTERVAL / 1000;
-      }
-      if (default_router_list[i].invalidation_timer < ND6_TMR_INTERVAL / 1000) {
-        /* Less than 1 second remainig. Clear this entry. */
-        default_router_list[i].neighbor_entry->isrouter = 0;
-        default_router_list[i].neighbor_entry = NULL;
-        default_router_list[i].invalidation_timer = 0;
-        default_router_list[i].flags = 0;
-      }
-    }
-  }
-
-  /* Process prefix entries. */
-  for (i = 0; i < LWIP_ND6_NUM_PREFIXES; i++) {
-    if (prefix_list[i].invalidation_timer < ND6_TMR_INTERVAL / 1000) {
-      prefix_list[i].invalidation_timer = 0;
-    }
-    if ((prefix_list[i].invalidation_timer > 0) &&
-        (prefix_list[i].netif != NULL)) {
-      prefix_list[i].invalidation_timer -= ND6_TMR_INTERVAL / 1000;
-
-#if LWIP_IPV6_AUTOCONFIG
-      /* Initiate address autoconfiguration for this prefix, if conditions are met. */
-      if (prefix_list[i].netif->ip6_autoconfig_enabled &&
-          (prefix_list[i].flags & ND6_PREFIX_AUTOCONFIG_AUTONOMOUS) &&
-          !(prefix_list[i].flags & ND6_PREFIX_AUTOCONFIG_ADDRESS_GENERATED)) {
-        /* Try to get an address on this netif that is invalid.
-         * Skip 0 index (link-local address) */
-        for (j = 1; j < LWIP_IPV6_NUM_ADDRESSES; j++) {
-          if (netif_ip6_addr_state(prefix_list[i].netif, j) == IP6_ADDRESS_STATE_INVALID) {
-            /* Generate an address using this prefix and interface ID from link-local address. */
-            prefix_list[i].netif->ip6_addr[j].addr[0] = prefix_list[i].prefix.addr[0];
-            prefix_list[i].netif->ip6_addr[j].addr[1] = prefix_list[i].prefix.addr[1];
-            prefix_list[i].netif->ip6_addr[j].addr[2] = prefix_list[i].netif->ip6_addr[0].addr[2];
-            prefix_list[i].netif->ip6_addr[j].addr[3] = prefix_list[i].netif->ip6_addr[0].addr[3];
-
-            /* Mark it as tentative (DAD will be performed if configured). */
-            netif_ip6_addr_set_state(prefix_list[i].netif, j, IP6_ADDR_TENTATIVE);
-
-            /* Mark this prefix with ADDRESS_GENERATED, so that we don't try again. */
-            prefix_list[i].flags |= ND6_PREFIX_AUTOCONFIG_ADDRESS_GENERATED;
-
-            /* Exit loop. */
-            break;
-          }
-        }
-      }
-#endif /* LWIP_IPV6_AUTOCONFIG */
-    }
-  }
-
-
-  /* Process our own addresses, if DAD configured. */
-  for (netif = netif_list; netif != NULL; netif = netif->next) {
-    for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; ++i) {
-      if (ip6_addr_istentative(netif->ip6_addr_state[i])) {
-        if ((netif->ip6_addr_state[i] & 0x07) >= LWIP_IPV6_DUP_DETECT_ATTEMPTS) {
-          /* No NA received in response. Mark address as valid. */
-          netif->ip6_addr_state[i] = IP6_ADDR_PREFERRED;
-          /* TODO implement preferred and valid lifetimes. */
-        }
-        else if (netif->flags & NETIF_FLAG_UP) {
-#if LWIP_IPV6_MLD
-          if ((netif->ip6_addr_state[i] & 0x07) == 0) {
-            /* Join solicited node multicast group. */
-            ip6_addr_set_solicitednode(&multicast_address, netif_ip6_addr(netif, i)->addr[3]);
-            mld6_joingroup(netif_ip6_addr(netif, i), &multicast_address);
-          }
-#endif /* LWIP_IPV6_MLD */
-          /* Send a NS for this address. */
-          nd6_send_ns(netif, netif_ip6_addr(netif, i), ND6_SEND_FLAG_MULTICAST_DEST);
-          (netif->ip6_addr_state[i])++;
-          /* TODO send max 1 NS per tmr call? enable return*/
-          /*return;*/
-        }
-      }
-    }
-  }
-
-#if LWIP_IPV6_SEND_ROUTER_SOLICIT
-  /* Send router solicitation messages, if necessary. */
-  for (netif = netif_list; netif != NULL; netif = netif->next) {
-    if ((netif->rs_count > 0) && (netif->flags & NETIF_FLAG_UP)) {
-      nd6_send_rs(netif);
-      netif->rs_count--;
-    }
-  }
-#endif /* LWIP_IPV6_SEND_ROUTER_SOLICIT */
-
-}
-
-/**
- * Send a neighbor solicitation message
- *
- * @param netif the netif on which to send the message
- * @param target_addr the IPv6 target address for the ND message
- * @param flags one of ND6_SEND_FLAG_*
- */
-static void
-nd6_send_ns(struct netif * netif, ip6_addr_t * target_addr, u8_t flags)
-{
-  struct ns_header * ns_hdr;
-  struct lladdr_option * lladdr_opt;
-  u16_t lladdr_option_len;
-  struct pbuf * p;
-  ip6_addr_t * src_addr;
-
-  if (ip6_addr_isvalid(netif_ip6_addr_state(netif,0))) {
-    /* Use link-local address as source address. */
-    src_addr = netif_ip6_addr(netif, 0);
-  } else {
-    src_addr = IP6_ADDR_ANY;
-  }
-
-  /* Allocate a packet. */
-  lladdr_option_len = ((netif->hwaddr_len + 2) >> 3) + (((netif->hwaddr_len + 2) & 0x07) ? 1 : 0);
-  p = pbuf_alloc(PBUF_IP, sizeof(struct ns_header) + (lladdr_option_len << 3), PBUF_RAM);
-  if ((p == NULL) || (p->len < (sizeof(struct ns_header) +(lladdr_option_len << 3)))) {
-    /* We couldn't allocate a suitable pbuf for the ns. drop it. */
-    if (p != NULL) {
-      pbuf_free(p);
-    }
-    ND6_STATS_INC(nd6.memerr);
-    return;
-  }
-
-  /* Set fields. */
-  ns_hdr = (struct ns_header *)p->payload;
-  lladdr_opt = (struct lladdr_option *)((u8_t*)p->payload + sizeof(struct ns_header));
-
-  ns_hdr->type = ICMP6_TYPE_NS;
-  ns_hdr->code = 0;
-  ns_hdr->chksum = 0;
-  ns_hdr->reserved = 0;
-  ip6_addr_set(&(ns_hdr->target_address), target_addr);
-
-  memset(lladdr_opt, 0, lladdr_option_len << 3);
-  lladdr_opt->type = ND6_OPTION_TYPE_SOURCE_LLADDR;
-  lladdr_opt->length = ((netif->hwaddr_len + 2) >> 3) + (((netif->hwaddr_len + 2) & 0x07) ? 1 : 0);
-  SMEMCPY(lladdr_opt->addr, netif->hwaddr, netif->hwaddr_len);
-
-  /* Generate the solicited node address for the target address. */
-  if (flags & ND6_SEND_FLAG_MULTICAST_DEST) {
-    ip6_addr_set_solicitednode(&multicast_address, target_addr->addr[3]);
-    target_addr = &multicast_address;
-  }
-
-  ns_hdr->chksum = ip6_chksum_pseudo(p, IP6_NEXTH_ICMP6, p->len, src_addr,
-    target_addr);
-
-  /* Send the packet out. */
-  ND6_STATS_INC(nd6.xmit);
-  ip6_output_if(p, (src_addr == IP6_ADDR_ANY) ? NULL : src_addr, target_addr,
-      LWIP_ICMP6_HL, 0, IP6_NEXTH_ICMP6, netif);
-  pbuf_free(p);
-}
-
-/**
- * Send a neighbor advertisement message
- *
- * @param netif the netif on which to send the message
- * @param target_addr the IPv6 target address for the ND message
- * @param flags one of ND6_SEND_FLAG_*
- */
-static void
-nd6_send_na(struct netif * netif, ip6_addr_t * target_addr, u8_t flags)
-{
-  struct na_header * na_hdr;
-  struct lladdr_option * lladdr_opt;
-  u16_t lladdr_option_len;
-  struct pbuf * p;
-  ip6_addr_t * src_addr;
-  ip6_addr_t * dest_addr;
-
-  /* Use link-local address as source address. */
-  /* src_addr = &(netif->ip6_addr[0]); */
-  /* Use target address as source address. */
-  src_addr = target_addr;
-
-  /* Allocate a packet. */
-  lladdr_option_len = ((netif->hwaddr_len + 2) >> 3) + (((netif->hwaddr_len + 2) & 0x07) ? 1 : 0);
-  p = pbuf_alloc(PBUF_IP, sizeof(struct na_header) + (lladdr_option_len << 3), PBUF_RAM);
-  if ((p == NULL) || (p->len < (sizeof(struct na_header) + (lladdr_option_len << 3)))) {
-    /* We couldn't allocate a suitable pbuf for the ns. drop it. */
-    if (p != NULL) {
-      pbuf_free(p);
-    }
-    ND6_STATS_INC(nd6.memerr);
-    return;
-  }
-
-  /* Set fields. */
-  na_hdr = (struct na_header *)p->payload;
-  lladdr_opt = (struct lladdr_option *)((u8_t*)p->payload + sizeof(struct na_header));
-
-  na_hdr->type = ICMP6_TYPE_NA;
-  na_hdr->code = 0;
-  na_hdr->chksum = 0;
-  na_hdr->flags = flags & 0xf0;
-  na_hdr->reserved[0] = 0;
-  na_hdr->reserved[1] = 0;
-  na_hdr->reserved[2] = 0;
-  ip6_addr_set(&(na_hdr->target_address), target_addr);
-
-  memset(lladdr_opt, 0, lladdr_option_len << 3);
-  lladdr_opt->type = ND6_OPTION_TYPE_TARGET_LLADDR;
-  lladdr_opt->length = lladdr_option_len;
-  SMEMCPY(lladdr_opt->addr, netif->hwaddr, netif->hwaddr_len);
-
-  /* Generate the solicited node address for the target address. */
-  if (flags & ND6_SEND_FLAG_MULTICAST_DEST) {
-    ip6_addr_set_solicitednode(&multicast_address, target_addr->addr[3]);
-    dest_addr = &multicast_address;
-  }
-  else if (flags & ND6_SEND_FLAG_ALLNODES_DEST) {
-    ip6_addr_set_allnodes_linklocal(&multicast_address);
-    dest_addr = &multicast_address;
-  }
-  else {
-    dest_addr = ip6_current_src_addr();
-  }
-
-  na_hdr->chksum = ip6_chksum_pseudo(p, IP6_NEXTH_ICMP6, p->len, src_addr,
-    dest_addr);
-
-  /* Send the packet out. */
-  ND6_STATS_INC(nd6.xmit);
-  ip6_output_if(p, src_addr, dest_addr,
-      LWIP_ICMP6_HL, 0, IP6_NEXTH_ICMP6, netif);
-  pbuf_free(p);

-}
-
-#if LWIP_IPV6_SEND_ROUTER_SOLICIT
-/**
- * Send a router solicitation message
- *
- * @param netif the netif on which to send the message
- */
-static void
-nd6_send_rs(struct netif * netif)
-{
-  struct rs_header * rs_hdr;
-  struct lladdr_option * lladdr_opt;
-  u16_t lladdr_option_len;
-  struct pbuf * p;
-  ip6_addr_t * src_addr;
-  u16_t packet_len;
-
-  /* Link-local source address, or unspecified address? */
-  if (ip6_addr_isvalid(netif_ip6_addr_state(netif, 0))) {
-    src_addr = netif_ip6_addr(netif, 0);
-  }
-  else {
-    src_addr = IP6_ADDR_ANY;
-  }
-
-  /* Generate the all routers target address. */
-  ip6_addr_set_allrouters_linklocal(&multicast_address);
-
-  /* Allocate a packet. */
-  packet_len = sizeof(struct rs_header);
-  lladdr_option_len = ((netif->hwaddr_len + 2) >> 3) + (((netif->hwaddr_len + 2) & 0x07) ? 1 : 0);
-  if (src_addr != IP6_ADDR_ANY) {
-    packet_len += (lladdr_option_len << 3);
-  }
-  p = pbuf_alloc(PBUF_IP, packet_len, PBUF_RAM);
-  if ((p == NULL) || (p->len < packet_len)) {
-    /* We couldn't allocate a suitable pbuf for the ns. drop it. */
-    if (p != NULL) {
-      pbuf_free(p);
-    }
-    ND6_STATS_INC(nd6.memerr);
-    return;
-  }
-
-  /* Set fields. */
-  rs_hdr = (struct rs_header *)p->payload;
-
-  rs_hdr->type = ICMP6_TYPE_RS;
-  rs_hdr->code = 0;
-  rs_hdr->chksum = 0;
-  rs_hdr->reserved = 0;
-
-  if (src_addr != IP6_ADDR_ANY) {
-    /* Include our hw address. */
-    lladdr_opt = (struct lladdr_option *)((u8_t*)p->payload + sizeof(struct rs_header));
-    memset(lladdr_opt, 0, lladdr_option_len << 3);
-    lladdr_opt->type = ND6_OPTION_TYPE_SOURCE_LLADDR;
-    lladdr_opt->length = ((netif->hwaddr_len + 2) >> 3) + (((netif->hwaddr_len + 2) & 0x07) ? 1 : 0);
-    SMEMCPY(lladdr_opt->addr, netif->hwaddr, netif->hwaddr_len);
-  }
-
-  rs_hdr->chksum = ip6_chksum_pseudo(p, IP6_NEXTH_ICMP6, p->len, src_addr,
-    &multicast_address);
-
-  /* Send the packet out. */
-  ND6_STATS_INC(nd6.xmit);
-  ip6_output_if(p, src_addr, &multicast_address,
-      LWIP_ICMP6_HL, 0, IP6_NEXTH_ICMP6, netif);
-  pbuf_free(p);
-}
-#endif /* LWIP_IPV6_SEND_ROUTER_SOLICIT */
-
-/**
- * Search for a neighbor cache entry
- *
- * @param ip6addr the IPv6 address of the neighbor
- * @return The neighbor cache entry index that matched, -1 if no
- * entry is found
- */
-static s8_t
-nd6_find_neighbor_cache_entry(ip6_addr_t * ip6addr)
-{
-  s8_t i;
-  for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++) {
-    if (ip6_addr_cmp(ip6addr, &(neighbor_cache[i].next_hop_address))) {
-      return i;
-    }
-  }
-  return -1;
-}
-
-/**
- * Create a new neighbor cache entry.
- *
- * If no unused entry is found, will try to recycle an old entry
- * according to ad-hoc "age" heuristic.
- *
- * @return The neighbor cache entry index that was created, -1 if no
- * entry could be created
- */
-static s8_t
-nd6_new_neighbor_cache_entry(void)
-{
-  s8_t i;
-  s8_t j;
-  u32_t time;
-  
-#if LWIP_RPL
-  #include "netif/rpl/rplopt.h"
-  RPL_IPV6_NEIGHBOR_CALLBACK(ip6_current_src_addr());
-#endif
-  
-  /* First, try to find an empty entry. */
-  for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++) {
-    if (neighbor_cache[i].state == ND6_NO_ENTRY) {
-      return i;
-    }
-  }
-
-  /* We need to recycle an entry. in general, do not recycle if it is a router. */
-
-  /* Next, try to find a Stale entry. */
-  for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++) {
-    if ((neighbor_cache[i].state == ND6_STALE) &&
-        (!neighbor_cache[i].isrouter)) {
-      nd6_free_neighbor_cache_entry(i);
-      return i;
-    }
-  }
-
-  /* Next, try to find a Probe entry. */
-  for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++) {
-    if ((neighbor_cache[i].state == ND6_PROBE) &&
-        (!neighbor_cache[i].isrouter)) {
-      nd6_free_neighbor_cache_entry(i);
-      return i;
-    }
-  }
-
-  /* Next, try to find a Delayed entry. */
-  for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++) {
-    if ((neighbor_cache[i].state == ND6_DELAY) &&
-        (!neighbor_cache[i].isrouter)) {
-      nd6_free_neighbor_cache_entry(i);
-      return i;
-    }
-  }
-
-  /* Next, try to find the oldest reachable entry. */
-  time = 0xfffffffful;
-  j = -1;
-  for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++) {
-    if ((neighbor_cache[i].state == ND6_REACHABLE) &&
-        (!neighbor_cache[i].isrouter)) {
-      if (neighbor_cache[i].counter.reachable_time < time) {
-        j = i;
-        time = neighbor_cache[i].counter.reachable_time;
-      }
-    }
-  }
-  if (j >= 0) {
-    nd6_free_neighbor_cache_entry(j);
-    return j;
-  }
-
-  /* Next, find oldest incomplete entry without queued packets. */
-  time = 0;
-  j = -1;
-  for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++) {
-    if (
-        (neighbor_cache[i].q == NULL) &&
-        (neighbor_cache[i].state == ND6_INCOMPLETE) &&
-        (!neighbor_cache[i].isrouter)) {
-      if (neighbor_cache[i].counter.probes_sent >= time) {
-        j = i;
-        time = neighbor_cache[i].counter.probes_sent;
-      }
-    }
-  }
-  if (j >= 0) {
-    nd6_free_neighbor_cache_entry(j);
-    return j;
-  }
-
-  /* Next, find oldest incomplete entry with queued packets. */
-  time = 0;
-  j = -1;
-  for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++) {
-    if ((neighbor_cache[i].state == ND6_INCOMPLETE) &&
-        (!neighbor_cache[i].isrouter)) {
-      if (neighbor_cache[i].counter.probes_sent >= time) {
-        j = i;
-        time = neighbor_cache[i].counter.probes_sent;
-      }
-    }
-  }
-  if (j >= 0) {
-    nd6_free_neighbor_cache_entry(j);
-    return j;
-  }
-  
-  /* No more entries to try. */
-  return -1;
-}
-
-/**
- * Will free any resources associated with a neighbor cache
- * entry, and will mark it as unused.
- *
- * @param i the neighbor cache entry index to free
- */
-static void
-nd6_free_neighbor_cache_entry(s8_t i)
-{
-  if ((i < 0) || (i >= LWIP_ND6_NUM_NEIGHBORS)) {
-    return;
-  }
-#if LWIP_RPL
-  #include "netif/rpl/rplopt.h"
-  RPL_IPV6_NEIGHBOR_CALLBACK(&neighbor_cache[i].next_hop_address);
-#endif
-  
-  /* Free any queued packets. */
-  if (neighbor_cache[i].q != NULL) {
-    nd6_free_q(neighbor_cache[i].q);
-    neighbor_cache[i].q = NULL;
-  }
-
-  neighbor_cache[i].state = ND6_NO_ENTRY;
-  neighbor_cache[i].isrouter = 0;
-  neighbor_cache[i].netif = NULL;
-  neighbor_cache[i].counter.reachable_time = 0;
-  ip6_addr_set_zero(&(neighbor_cache[i].next_hop_address));
-}
-
-/**
- * Search for a destination cache entry
- *
- * @param ip6addr the IPv6 address of the destination
- * @return The destination cache entry index that matched, -1 if no
- * entry is found
- */
-static s8_t
-nd6_find_destination_cache_entry(ip6_addr_t * ip6addr)
-{
-  s8_t i;
-  for (i = 0; i < LWIP_ND6_NUM_DESTINATIONS; i++) {
-    if (ip6_addr_cmp(ip6addr, &(destination_cache[i].destination_addr))) {
-      return i;
-    }
-  }
-  return -1;
-}
-
-/**
- * Create a new destination cache entry. If no unused entry is found,
- * will recycle oldest entry.
- *
- * @return The destination cache entry index that was created, -1 if no
- * entry was created
- */
-static s8_t
-nd6_new_destination_cache_entry(void)
-{
-  s8_t i, j;
-  u32_t age;
-
-  /* Find an empty entry. */
-  for (i = 0; i < LWIP_ND6_NUM_DESTINATIONS; i++) {
-    if (ip6_addr_isany(&(destination_cache[i].destination_addr))) {
-      return i;
-    }
-  }
-
-  /* Find oldest entry. */
-  age = 0;
-  j = LWIP_ND6_NUM_DESTINATIONS - 1;
-  for (i = 0; i < LWIP_ND6_NUM_DESTINATIONS; i++) {
-    if (destination_cache[i].age > age) {
-      j = i;
-    }
-  }
-
-  return j;
-}
-
-/**
- * Determine whether an address matches an on-link prefix.
- *
- * @param ip6addr the IPv6 address to match
- * @return 1 if the address is on-link, 0 otherwise
- */
-static s8_t
-nd6_is_prefix_in_netif(ip6_addr_t * ip6addr, struct netif * netif)
-{
-  s8_t i;
-  for (i = 0; i < LWIP_ND6_NUM_PREFIXES; i++) {
-    if ((prefix_list[i].netif == netif) &&
-        (prefix_list[i].invalidation_timer > 0) &&
-        ip6_addr_netcmp(ip6addr, &(prefix_list[i].prefix))) {
-      return 1;
-    }
-  }
-  /* Check to see if address prefix matches a (manually?) configured address. */
-  for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; i++) {
-    if (ip6_addr_isvalid(netif_ip6_addr_state(netif, i)) &&
-        ip6_addr_netcmp(ip6addr, netif_ip6_addr(netif, i))) {
-      return 1;
-    }
-  }
-  return 0;
-}
-
-/**
- * Select a default router for a destination.
- *
- * @param ip6addr the destination address
- * @param netif the netif for the outgoing packet, if known
- * @return the default router entry index, or -1 if no suitable
- *         router is found
- */
-s8_t
-nd6_select_router(ip6_addr_t * ip6addr, struct netif * netif)
-{
-  s8_t i;
-  /* last_router is used for round-robin router selection (as recommended
-   * in RFC). This is more robust in case one router is not reachable,
-   * we are not stuck trying to resolve it. */
-  static s8_t last_router;
-  (void)ip6addr; /* TODO match preferred routes!! (must implement ND6_OPTION_TYPE_ROUTE_INFO) */
-
-  /* TODO: implement default router preference */
-
-  /* Look for reachable routers. */
-  for (i = 0; i < LWIP_ND6_NUM_ROUTERS; i++) {
-    if (++last_router >= LWIP_ND6_NUM_ROUTERS) {
-      last_router = 0;
-    }
-    if ((default_router_list[i].neighbor_entry != NULL) &&
-        (netif != NULL ? netif == default_router_list[i].neighbor_entry->netif : 1) &&
-        (default_router_list[i].invalidation_timer > 0) &&
-        (default_router_list[i].neighbor_entry->state == ND6_REACHABLE)) {
-      return i;
-    }
-  }
-
-  /* Look for router in other reachability states, but still valid according to timer. */
-  for (i = 0; i < LWIP_ND6_NUM_ROUTERS; i++) {
-    if (++last_router >= LWIP_ND6_NUM_ROUTERS) {
-      last_router = 0;
-    }
-    if ((default_router_list[i].neighbor_entry != NULL) &&
-        (netif != NULL ? netif == default_router_list[i].neighbor_entry->netif : 1) &&
-        (default_router_list[i].invalidation_timer > 0)) {
-      return i;
-    }
-  }
-
-  /* Look for any router for which we have any information at all. */
-  for (i = 0; i < LWIP_ND6_NUM_ROUTERS; i++) {
-    if (++last_router >= LWIP_ND6_NUM_ROUTERS) {
-      last_router = 0;
-    }
-    if (default_router_list[i].neighbor_entry != NULL &&
-        (netif != NULL ? netif == default_router_list[i].neighbor_entry->netif : 1)) {
-      return i;
-    }
-  }
-
-  /* no suitable router found. */
-  return -1;
-}
-
-/**
- * Find an entry for a default router.
- *
- * @param router_addr the IPv6 address of the router
- * @param netif the netif on which the router is found, if known
- * @return the index of the router entry, or -1 if not found
- */
-static s8_t
-nd6_get_router(ip6_addr_t * router_addr, struct netif * netif)
-{
-  s8_t i;
-
-  /* Look for router. */
-  for (i = 0; i < LWIP_ND6_NUM_ROUTERS; i++) {
-    if ((default_router_list[i].neighbor_entry != NULL) &&
-        ((netif != NULL) ? netif == default_router_list[i].neighbor_entry->netif : 1) &&
-        ip6_addr_cmp(router_addr, &(default_router_list[i].neighbor_entry->next_hop_address))) {
-      return i;
-    }
-  }
-
-  /* router not found. */
-  return -1;
-}
-
-/**
- * Create a new entry for a default router.
- *
- * @param router_addr the IPv6 address of the router
- * @param netif the netif on which the router is connected, if known
- * @return the index on the router table, or -1 if could not be created
- */
-static s8_t
-nd6_new_router(ip6_addr_t * router_addr, struct netif * netif)
-{
-  s8_t router_index;
-  s8_t neighbor_index;
-
-  /* Do we have a neighbor entry for this router? */
-  neighbor_index = nd6_find_neighbor_cache_entry(router_addr);
-  if (neighbor_index < 0) {
-    /* Create a neighbor entry for this router. */
-    neighbor_index = nd6_new_neighbor_cache_entry();
-    if (neighbor_index < 0) {
-      /* Could not create neighbor entry for this router. */
-      return -1;
-    }
-    ip6_addr_set(&(neighbor_cache[neighbor_index].next_hop_address), router_addr);
-    neighbor_cache[neighbor_index].netif = netif;
-    neighbor_cache[neighbor_index].q = NULL;
-    neighbor_cache[neighbor_index].state = ND6_INCOMPLETE;
-    neighbor_cache[neighbor_index].counter.probes_sent = 0;
-  }
-
-  /* Mark neighbor as router. */
-  neighbor_cache[neighbor_index].isrouter = 1;
-
-  /* Look for empty entry. */
-  for (router_index = 0; router_index < LWIP_ND6_NUM_ROUTERS; router_index++) {
-    if (default_router_list[router_index].neighbor_entry == NULL) {
-      default_router_list[router_index].neighbor_entry = &(neighbor_cache[neighbor_index]);
-      return router_index;
-    }
-  }
-
-  /* Could not create a router entry. */
-
-  /* Mark neighbor entry as not-router. Entry might be useful as neighbor still. */
-  neighbor_cache[neighbor_index].isrouter = 0;
-
-  /* router not found. */
-  return -1;
-}
-
-/**
- * Find the cached entry for an on-link prefix.
- *
- * @param prefix the IPv6 prefix that is on-link
- * @param netif the netif on which the prefix is on-link
- * @return the index on the prefix table, or -1 if not found
- */
-static s8_t
-nd6_get_onlink_prefix(ip6_addr_t * prefix, struct netif * netif)
-{
-  s8_t i;
-
-  /* Look for prefix in list. */
-  for (i = 0; i < LWIP_ND6_NUM_PREFIXES; ++i) {
-    if ((ip6_addr_netcmp(&(prefix_list[i].prefix), prefix)) &&
-        (prefix_list[i].netif == netif)) {
-      return i;
-    }
-  }
-
-  /* Entry not available. */
-  return -1;
-}
-
-/**
- * Creates a new entry for an on-link prefix.
- *
- * @param prefix the IPv6 prefix that is on-link
- * @param netif the netif on which the prefix is on-link
- * @return the index on the prefix table, or -1 if not created
- */
-static s8_t
-nd6_new_onlink_prefix(ip6_addr_t * prefix, struct netif * netif)
-{
-  s8_t i;
-
-  /* Create new entry. */
-  for (i = 0; i < LWIP_ND6_NUM_PREFIXES; ++i) {
-    if ((prefix_list[i].netif == NULL) ||
-        (prefix_list[i].invalidation_timer == 0)) {
-      /* Found empty prefix entry. */
-      prefix_list[i].netif = netif;
-      ip6_addr_set(&(prefix_list[i].prefix), prefix);
-      prefix_list[i].flags = 0;
-      return i;
-    }
-  }
-
-  /* Entry not available. */
-  return -1;
-}
-
-/**
- * Determine the next hop for a destination. Will determine if the
- * destination is on-link, else a suitable on-link router is selected.
- *
- * The last entry index is cached for fast entry search.
- *
- * @param ip6addr the destination address
- * @param netif the netif on which the packet will be sent
- * @return the neighbor cache entry for the next hop, ERR_RTE if no
- *         suitable next hop was found, ERR_MEM if no cache entry
- *         could be created
- */
-s8_t
-nd6_get_next_hop_entry(ip6_addr_t * ip6addr, struct netif * netif)
-{
-  s8_t i;
-
-#if LWIP_NETIF_HWADDRHINT
-  if (netif->addr_hint != NULL) {
-    /* per-pcb cached entry was given */
-    u8_t addr_hint = *(netif->addr_hint);
-    if (addr_hint < LWIP_ND6_NUM_DESTINATIONS) {
-      nd6_cached_destination_index = addr_hint;
-    }
-  }
-#endif /* LWIP_NETIF_HWADDRHINT */
-
-  /* Look for ip6addr in destination cache. */
-  if (ip6_addr_cmp(ip6addr, &(destination_cache[nd6_cached_destination_index].destination_addr))) {
-    /* the cached entry index is the right one! */
-    /* do nothing. */
-    ND6_STATS_INC(nd6.cachehit);
-  } else {
-    /* Search destination cache. */
-    i = nd6_find_destination_cache_entry(ip6addr);
-    if (i >= 0) {
-      /* found destination entry. make it our new cached index. */
-      nd6_cached_destination_index = i;
-    }
-    else {
-      /* Not found. Create a new destination entry. */
-      i = nd6_new_destination_cache_entry();
-      if (i >= 0) {
-        /* got new destination entry. make it our new cached index. */
-        nd6_cached_destination_index = i;
-      } else {
-        /* Could not create a destination cache entry. */
-        return ERR_MEM;
-      }
-
-      /* Copy dest address to destination cache. */
-      ip6_addr_set(&(destination_cache[nd6_cached_destination_index].destination_addr), ip6addr);
-
-      /* Now find the next hop. is it a neighbor? */
-      if (ip6_addr_islinklocal(ip6addr) ||
-          nd6_is_prefix_in_netif(ip6addr, netif)) {
-        /* Destination in local link. */
-        destination_cache[nd6_cached_destination_index].pmtu = netif->mtu;
-        ip6_addr_copy(destination_cache[nd6_cached_destination_index].next_hop_addr, destination_cache[nd6_cached_destination_index].destination_addr);
-      }
-      else {
-        /* We need to select a router. */
-        i = nd6_select_router(ip6addr, netif);
-        if (i < 0) {
-          /* No router found. */
-          ip6_addr_set_any(&(destination_cache[nd6_cached_destination_index].destination_addr));
-          return ERR_RTE;
-        }
-        destination_cache[nd6_cached_destination_index].pmtu = netif->mtu; /* Start with netif mtu, correct through ICMPv6 if necessary */
-        ip6_addr_copy(destination_cache[nd6_cached_destination_index].next_hop_addr, default_router_list[i].neighbor_entry->next_hop_address);
-      }
-    }
-  }
-
-#if LWIP_NETIF_HWADDRHINT
-  if (netif->addr_hint != NULL) {
-    /* per-pcb cached entry was given */
-    *(netif->addr_hint) = nd6_cached_destination_index;
-  }
-#endif /* LWIP_NETIF_HWADDRHINT */
-
-  /* Look in neighbor cache for the next-hop address. */
-  if (ip6_addr_cmp(&(destination_cache[nd6_cached_destination_index].next_hop_addr),
-                   &(neighbor_cache[nd6_cached_neighbor_index].next_hop_address))) {
-    /* Cache hit. */
-    /* Do nothing. */
-    ND6_STATS_INC(nd6.cachehit);
-  } else {
-    i = nd6_find_neighbor_cache_entry(&(destination_cache[nd6_cached_destination_index].next_hop_addr));
-    if (i >= 0) {
-      /* Found a matching record, make it new cached entry. */
-      nd6_cached_neighbor_index = i;
-    }
-    else {
-      /* Neighbor not in cache. Make a new entry. */
-      i = nd6_new_neighbor_cache_entry();
-      if (i >= 0) {
-        /* got new neighbor entry. make it our new cached index. */
-        nd6_cached_neighbor_index = i;
-      } else {
-        /* Could not create a neighbor cache entry. */
-        return ERR_MEM;
-      }
-
-      /* Initialize fields. */
-      ip6_addr_copy(neighbor_cache[i].next_hop_address,
-                   destination_cache[nd6_cached_destination_index].next_hop_addr);
-      neighbor_cache[i].isrouter = 0;
-      neighbor_cache[i].netif = netif;
-      neighbor_cache[i].state = ND6_INCOMPLETE;
-      neighbor_cache[i].counter.probes_sent = 0;
-    }
-  }
-
-  /* Reset this destination's age. */
-  destination_cache[nd6_cached_destination_index].age = 0;
-
-  return nd6_cached_neighbor_index;
-}
-
-/**
- * Queue a packet for a neighbor.
- *
- * @param neighbor_index the index in the neighbor cache table
- * @param q packet to be queued
- * @return ERR_OK if succeeded, ERR_MEM if out of memory
- */
-err_t
-nd6_queue_packet(s8_t neighbor_index, struct pbuf * q)
-{
-  err_t result = ERR_MEM;
-  struct pbuf *p;
-  int copy_needed = 0;
-#if LWIP_ND6_QUEUEING
-  struct nd6_q_entry *new_entry, *r;
-#endif /* LWIP_ND6_QUEUEING */
-
-  if ((neighbor_index < 0) || (neighbor_index >= LWIP_ND6_NUM_NEIGHBORS)) {
-    return ERR_ARG;
-  }
-
-  /* IF q includes a PBUF_REF, PBUF_POOL or PBUF_RAM, we have no choice but
-   * to copy the whole queue into a new PBUF_RAM (see bug #11400)
-   * PBUF_ROMs can be left as they are, since ROM must not get changed. */
-  p = q;
-  while (p) {
-    if(p->type != PBUF_ROM) {
-      copy_needed = 1;
-      break;
-    }
-    p = p->next;
-  }
-  if(copy_needed) {
-    /* copy the whole packet into new pbufs */
-    p = pbuf_alloc(PBUF_LINK, q->tot_len, PBUF_RAM);
-    while ((p == NULL) && (neighbor_cache[neighbor_index].q != NULL)) {
-      /* Free oldest packet (as per RFC recommendation) */
-#if LWIP_ND6_QUEUEING
-      r = neighbor_cache[neighbor_index].q;
-      neighbor_cache[neighbor_index].q = r->next;
-      r->next = NULL;
-      nd6_free_q(r);
-#else /* LWIP_ND6_QUEUEING */
-      pbuf_free(neighbor_cache[neighbor_index].q);
-      neighbor_cache[neighbor_index].q = NULL;
-#endif /* LWIP_ND6_QUEUEING */
-      p = pbuf_alloc(PBUF_LINK, q->tot_len, PBUF_RAM);
-    }
-    if(p != NULL) {
-      if (pbuf_copy(p, q) != ERR_OK) {
-        pbuf_free(p);
-        p = NULL;
-      }
-    }
-  } else {
-    /* referencing the old pbuf is enough */
-    p = q;
-    pbuf_ref(p);
-  }
-  /* packet was copied/ref'd? */
-  if (p != NULL) {
-    /* queue packet ... */
-#if LWIP_ND6_QUEUEING
-    /* allocate a new nd6 queue entry */
-    new_entry = (struct nd6_q_entry *)memp_malloc(MEMP_ND6_QUEUE);
-    if ((new_entry == NULL) && (neighbor_cache[neighbor_index].q != NULL)) {
-      /* Free oldest packet (as per RFC recommendation) */
-      r = neighbor_cache[neighbor_index].q;
-      neighbor_cache[neighbor_index].q = r->next;
-      r->next = NULL;
-      nd6_free_q(r);
-      new_entry = (struct nd6_q_entry *)memp_malloc(MEMP_ND6_QUEUE);
-    }
-    if (new_entry != NULL) {
-      new_entry->next = NULL;
-      new_entry->p = p;
-      if(neighbor_cache[neighbor_index].q != NULL) {
-        /* queue was already existent, append the new entry to the end */
-        r = neighbor_cache[neighbor_index].q;
-        while (r->next != NULL) {
-          r = r->next;
-        }
-        r->next = new_entry;
-      } else {
-        /* queue did not exist, first item in queue */
-        neighbor_cache[neighbor_index].q = new_entry;
-      }
-      LWIP_DEBUGF(LWIP_DBG_TRACE, ("ipv6: queued packet %p on neighbor entry %"S16_F"\n", (void *)p, (s16_t)neighbor_index));
-      result = ERR_OK;
-    } else {
-      /* the pool MEMP_ND6_QUEUE is empty */
-      pbuf_free(p);
-      LWIP_DEBUGF(LWIP_DBG_TRACE, ("ipv6: could not queue a copy of packet %p (out of memory)\n", (void *)p));
-      /* { result == ERR_MEM } through initialization */
-    }
-#else /* LWIP_ND6_QUEUEING */
-    /* Queue a single packet. If an older packet is already queued, free it as per RFC. */
-    if (neighbor_cache[neighbor_index].q != NULL) {
-      pbuf_free(neighbor_cache[neighbor_index].q);
-    }
-    neighbor_cache[neighbor_index].q = p;
-    LWIP_DEBUGF(LWIP_DBG_TRACE, ("ipv6: queued packet %p on neighbor entry %"S16_F"\n", (void *)p, (s16_t)neighbor_index));
-    result = ERR_OK;
-#endif /* LWIP_ND6_QUEUEING */
-  } else {
-    LWIP_DEBUGF(LWIP_DBG_TRACE, ("ipv6: could not queue a copy of packet %p (out of memory)\n", (void *)q));
-    /* { result == ERR_MEM } through initialization */
-  }
-
-  return result;
-}
-
-#if LWIP_ND6_QUEUEING
-/**
- * Free a complete queue of nd6 q entries
- *
- * @param q a queue of nd6_q_entry to free
- */
-static void
-nd6_free_q(struct nd6_q_entry *q)
-{
-  struct nd6_q_entry *r;
-  LWIP_ASSERT("q != NULL", q != NULL);
-  LWIP_ASSERT("q->p != NULL", q->p != NULL);
-  while (q) {
-    r = q;
-    q = q->next;
-    LWIP_ASSERT("r->p != NULL", (r->p != NULL));
-    pbuf_free(r->p);
-    memp_free(MEMP_ND6_QUEUE, r);
-  }
-}
-#endif /* LWIP_ND6_QUEUEING */
-
-/**
- * Send queued packets for a neighbor
- *
- * @param i the neighbor to send packets to
- */
-static void
-nd6_send_q(s8_t i)
-{
-  struct ip6_hdr *ip6hdr;
-#if LWIP_ND6_QUEUEING
-  struct nd6_q_entry *q;
-#endif /* LWIP_ND6_QUEUEING */
-
-  if ((i < 0) || (i >= LWIP_ND6_NUM_NEIGHBORS)) {
-    return;
-  }
-
-#if LWIP_ND6_QUEUEING
-  while (neighbor_cache[i].q != NULL) {
-    /* remember first in queue */
-    q = neighbor_cache[i].q;
-    /* pop first item off the queue */
-    neighbor_cache[i].q = q->next;
-    /* Get ipv6 header. */
-    ip6hdr = (struct ip6_hdr *)(q->p->payload);
-    /* Override ip6_current_dest_addr() so that we have an aligned copy. */
-    ip6_addr_set(ip6_current_dest_addr(), &(ip6hdr->dest));
-    /* send the queued IPv6 packet */
-    (neighbor_cache[i].netif)->output_ip6(neighbor_cache[i].netif, q->p, ip6_current_dest_addr());
-    /* free the queued IP packet */
-    pbuf_free(q->p);
-    /* now queue entry can be freed */
-    memp_free(MEMP_ND6_QUEUE, q);
-  }
-#else /* LWIP_ND6_QUEUEING */
-  if (neighbor_cache[i].q != NULL) {
-    /* Get ipv6 header. */
-    ip6hdr = (struct ip6_hdr *)(neighbor_cache[i].q->payload);
-    /* Override ip6_current_dest_addr() so that we have an aligned copy. */
-    ip6_addr_set(ip6_current_dest_addr(), &(ip6hdr->dest));
-    /* send the queued IPv6 packet */
-    (neighbor_cache[i].netif)->output_ip6(neighbor_cache[i].netif, neighbor_cache[i].q, ip6_current_dest_addr());
-    /* free the queued IP packet */
-    pbuf_free(neighbor_cache[i].q);
-    neighbor_cache[i].q = NULL;
-  }
-#endif /* LWIP_ND6_QUEUEING */
-}
-
-
-/**
- * Get the Path MTU for a destination.
- *
- * @param ip6addr the destination address
- * @param netif the netif on which the packet will be sent
- * @return the Path MTU, if known, or the netif default MTU
- */
-u16_t
-nd6_get_destination_mtu(ip6_addr_t * ip6addr, struct netif * netif)
-{
-  s8_t i;
-
-  i = nd6_find_destination_cache_entry(ip6addr);
-  if (i >= 0) {
-    if (destination_cache[i].pmtu > 0) {
-      return destination_cache[i].pmtu;
-    }
-  }
-
-  if (netif != NULL) {
-    return netif->mtu;
-  }
-
-  return 1280; /* Minimum MTU */
-}
-
-/**
- * Get the Path MTU for a destination.
- *
- * @param ip6addr the destination address
- * @param netif the netif on which the packet will be sent
- * @return the Path MTU, if known, or the netif default MTU
- */
-void
-nd6_neighbor_cach_add(u8_t *hwaddr, ip6_addr_t * ip6addr,
-                      u8_t state, struct netif * netif)
-{
-   s8_t i;
-
-   i = nd6_find_neighbor_cache_entry(ip6addr);
-   if(i < 0) {
-      /* Add their IPv6 address and link-layer address to neighbor cache.
-       * We will need it at least to send a unicast NA message, but most
-       * likely we will also be communicating with this node soon. */
-     i = nd6_new_neighbor_cache_entry();
-     if (i < 0) {
-     /* We couldn't assign a cache entry for this neighbor.
-      * we won't be able to reply. drop it. */
-       ND6_STATS_INC(nd6.memerr);
-       return;
-     }
-   }
-   neighbor_cache[i].netif = netif;
-   MEMCPY(neighbor_cache[i].lladdr, hwaddr, netif->hwaddr_len);
-   ip6_addr_set(&(neighbor_cache[i].next_hop_address), ip6addr);
-   if(state == ND6_INCOMPLETE) {
-     neighbor_cache[i].state = ND6_INCOMPLETE;
-     neighbor_cache[i].counter.delay_time = LWIP_ND6_DELAY_FIRST_PROBE_TIME;
-   } else {
-     neighbor_cache[i].state = ND6_REACHABLE;
-     neighbor_cache[i].counter.reachable_time = LWIP_ND6_REACHABLE_TIME;
-   }
-}
-
-#if LWIP_ND6_TCP_REACHABILITY_HINTS
-/**
- * Provide the Neighbor discovery process with a hint that a
- * destination is reachable. Called by tcp_receive when ACKs are
- * received or sent (as per RFC). This is useful to avoid sending
- * NS messages every 30 seconds.
- *
- * @param ip6addr the destination address which is know to be reachable
- *                by an upper layer protocol (TCP)
- */
-void
-nd6_reachability_hint(ip6_addr_t * ip6addr)
-{
-  s8_t i;
-
-  /* Find destination in cache. */
-  if (ip6_addr_cmp(ip6addr, &(destination_cache[nd6_cached_destination_index].destination_addr))) {
-    i = nd6_cached_destination_index;
-    ND6_STATS_INC(nd6.cachehit);
-  }
-  else {
-    i = nd6_find_destination_cache_entry(ip6addr);
-  }
-  if (i < 0) {
-    return;
-  }
-
-  /* Find next hop neighbor in cache. */
-  if (ip6_addr_cmp(&(destination_cache[i].next_hop_addr), &(neighbor_cache[nd6_cached_neighbor_index].next_hop_address))) {
-    i = nd6_cached_neighbor_index;
-    ND6_STATS_INC(nd6.cachehit);
-  }
-  else {
-    i = nd6_find_neighbor_cache_entry(&(destination_cache[i].next_hop_addr));
-  }
-  if (i < 0) {
-    return;
-  }
-
-  /* Set reachability state. */
-  neighbor_cache[i].state = ND6_REACHABLE;
-  neighbor_cache[i].counter.reachable_time = reachable_time;
-}
-#endif /* LWIP_ND6_TCP_REACHABILITY_HINTS */
-
-#endif /* LWIP_IPV6 */
+/**
+ * @file
+ *
+ * Neighbor discovery and stateless address autoconfiguration for IPv6.
+ * Aims to be compliant with RFC 4861 (Neighbor discovery) and RFC 4862
+ * (Address autoconfiguration).
+ */
+
+/*
+ * Copyright (c) 2010 Inico Technologies Ltd.
+ * 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. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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 lwIP TCP/IP stack.
+ *
+ * Author: Ivan Delamer <delamer@inicotech.com>
+ *
+ *
+ * Please coordinate changes and requests with Ivan Delamer
+ * <delamer@inicotech.com>
+ */
+
+#include "lwip/opt.h"
+
+#if LWIP_IPV6  /* don't build if not configured for use in lwipopts.h */
+
+#include "lwip/nd6.h"
+#include "lwip/pbuf.h"
+#include "lwip/mem.h"
+#include "lwip/memp.h"
+#include "lwip/ip6.h"
+#include "lwip/ip6_addr.h"
+#include "lwip/inet_chksum.h"
+#include "lwip/netif.h"
+#include "lwip/icmp6.h"
+#include "lwip/mld6.h"
+#include "lwip/ip.h"
+#include "lwip/stats.h"
+
+#include <string.h>
+
+
+/* Router tables. */
+struct nd6_neighbor_cache_entry neighbor_cache[LWIP_ND6_NUM_NEIGHBORS];
+struct nd6_destination_cache_entry destination_cache[LWIP_ND6_NUM_DESTINATIONS];
+struct nd6_prefix_list_entry prefix_list[LWIP_ND6_NUM_PREFIXES];
+struct nd6_router_list_entry default_router_list[LWIP_ND6_NUM_ROUTERS];
+
+/* Default values, can be updated by a RA message. */
+u32_t reachable_time = LWIP_ND6_REACHABLE_TIME;
+u32_t retrans_timer = LWIP_ND6_RETRANS_TIMER; /* TODO implement this value in timer */
+
+/* Index for cache entries. */
+static u8_t nd6_cached_neighbor_index;
+static u8_t nd6_cached_destination_index;
+
+/* Multicast address holder. */
+static ip6_addr_t multicast_address;
+
+/* Static buffer to parse RA packet options (size of a prefix option, biggest option) */
+static u8_t nd6_ra_buffer[sizeof(struct prefix_option)];
+
+/* Forward declarations. */
+static s8_t nd6_find_neighbor_cache_entry(ip6_addr_t * ip6addr);
+static s8_t nd6_new_neighbor_cache_entry(void);
+static void nd6_free_neighbor_cache_entry(s8_t i);
+static s8_t nd6_find_destination_cache_entry(ip6_addr_t * ip6addr);
+static s8_t nd6_new_destination_cache_entry(void);
+static s8_t nd6_is_prefix_in_netif(ip6_addr_t * ip6addr, struct netif * netif);
+static s8_t nd6_get_router(ip6_addr_t * router_addr, struct netif * netif);
+static s8_t nd6_new_router(ip6_addr_t * router_addr, struct netif * netif);
+static s8_t nd6_get_onlink_prefix(ip6_addr_t * prefix, struct netif * netif);
+static s8_t nd6_new_onlink_prefix(ip6_addr_t * prefix, struct netif * netif);
+
+#define ND6_SEND_FLAG_MULTICAST_DEST 0x01
+#define ND6_SEND_FLAG_ALLNODES_DEST 0x02
+static void nd6_send_ns(struct netif * netif, ip6_addr_t * target_addr, u8_t flags);
+static void nd6_send_na(struct netif * netif, ip6_addr_t * target_addr, u8_t flags);
+#if LWIP_IPV6_SEND_ROUTER_SOLICIT
+static void nd6_send_rs(struct netif * netif);
+#endif /* LWIP_IPV6_SEND_ROUTER_SOLICIT */
+
+#if LWIP_ND6_QUEUEING
+static void nd6_free_q(struct nd6_q_entry *q);
+#else /* LWIP_ND6_QUEUEING */
+#define nd6_free_q(q) pbuf_free(q)
+#endif /* LWIP_ND6_QUEUEING */
+static void nd6_send_q(s8_t i);
+
+
+/**
+ * Process an incoming neighbor discovery message
+ *
+ * @param p the nd packet, p->payload pointing to the icmpv6 header
+ * @param inp the netif on which this packet was received
+ */
+void
+nd6_input(struct pbuf *p, struct netif *inp)
+{
+  u8_t msg_type;
+  s8_t i;
+
+  ND6_STATS_INC(nd6.recv);
+
+  msg_type = *((u8_t *)p->payload);
+  switch (msg_type) {
+  case ICMP6_TYPE_NA: /* Neighbor Advertisement. */
+  {
+    struct na_header * na_hdr;
+    struct lladdr_option * lladdr_opt;
+
+    /* Check that na header fits in packet. */
+    if (p->len < (sizeof(struct na_header))) {
+      /* TODO debug message */
+      pbuf_free(p);
+      ND6_STATS_INC(nd6.lenerr);
+      ND6_STATS_INC(nd6.drop);
+      return;
+    }
+
+    na_hdr = (struct na_header *)p->payload;
+
+    /* Unsolicited NA?*/
+    if (ip6_addr_ismulticast(ip6_current_dest_addr())) {
+      /* This is an unsolicited NA.
+       * link-layer changed?
+       * part of DAD mechanism? */
+
+      /* Check that link-layer address option also fits in packet. */
+      if (p->len < (sizeof(struct na_header) + sizeof(struct lladdr_option))) {
+        /* TODO debug message */
+        pbuf_free(p);
+        ND6_STATS_INC(nd6.lenerr);
+        ND6_STATS_INC(nd6.drop);
+        return;
+      }
+
+      lladdr_opt = (struct lladdr_option *)((u8_t*)p->payload + sizeof(struct na_header));
+
+      /* Override ip6_current_dest_addr() so that we have an aligned copy. */
+      ip6_addr_set(ip6_current_dest_addr(), &(na_hdr->target_address));
+
+#if LWIP_IPV6_DUP_DETECT_ATTEMPTS
+      /* If the target address matches this netif, it is a DAD response. */
+      for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; i++) {
+        if (ip6_addr_cmp(ip6_current_dest_addr(), netif_ip6_addr(inp, i))) {
+          /* We are using a duplicate address. */
+          netif_ip6_addr_set_state(inp, i, IP6_ADDR_INVALID);
+
+#if LWIP_IPV6_MLD
+          /* Leave solicited node multicast group. */
+          ip6_addr_set_solicitednode(&multicast_address, netif_ip6_addr(inp, i)->addr[3]);
+          mld6_leavegroup(netif_ip6_addr(inp, i), &multicast_address);
+#endif /* LWIP_IPV6_MLD */
+
+
+
+
+#if LWIP_IPV6_AUTOCONFIG
+          /* Check to see if this address was autoconfigured. */
+          if (!ip6_addr_islinklocal(ip6_current_dest_addr())) {
+            i = nd6_get_onlink_prefix(ip6_current_dest_addr(), inp);
+            if (i >= 0) {
+              /* Mark this prefix as duplicate, so that we don't use it
+               * to generate this address again. */
+              prefix_list[i].flags |= ND6_PREFIX_AUTOCONFIG_ADDRESS_DUPLICATE;
+            }
+          }
+#endif /* LWIP_IPV6_AUTOCONFIG */
+
+          pbuf_free(p);
+          return;
+        }
+      }
+#endif /* LWIP_IPV6_DUP_DETECT_ATTEMPTS */
+
+      /* This is an unsolicited NA, most likely there was a LLADDR change. */
+      i = nd6_find_neighbor_cache_entry(ip6_current_dest_addr());
+      if (i >= 0) {
+        if (na_hdr->flags & ND6_FLAG_OVERRIDE) {
+          MEMCPY(neighbor_cache[i].lladdr, lladdr_opt->addr, inp->hwaddr_len);
+        }
+      }
+    }
+    else {
+      /* This is a solicited NA.
+       * neighbor address resolution response?
+       * neighbor unreachability detection response? */
+
+      /* Override ip6_current_dest_addr() so that we have an aligned copy. */
+      ip6_addr_set(ip6_current_dest_addr(), &(na_hdr->target_address));
+
+      /* Find the cache entry corresponding to this na. */
+      i = nd6_find_neighbor_cache_entry(ip6_current_dest_addr());
+      if (i < 0) {
+        /* We no longer care about this target address. drop it. */
+        pbuf_free(p);
+        return;
+      }
+
+      /* Update cache entry. */
+      neighbor_cache[i].netif = inp;
+      neighbor_cache[i].counter.reachable_time = reachable_time;
+      if ((na_hdr->flags & ND6_FLAG_OVERRIDE) ||
+          (neighbor_cache[i].state == ND6_INCOMPLETE)) {
+        /* Check that link-layer address option also fits in packet. */
+        if (p->len < (sizeof(struct na_header) + sizeof(struct lladdr_option))) {
+          /* TODO debug message */
+          pbuf_free(p);
+          ND6_STATS_INC(nd6.lenerr);
+          ND6_STATS_INC(nd6.drop);
+          return;
+        }
+
+        lladdr_opt = (struct lladdr_option *)((u8_t*)p->payload + sizeof(struct na_header));
+
+        MEMCPY(neighbor_cache[i].lladdr, lladdr_opt->addr, inp->hwaddr_len);
+      }
+      neighbor_cache[i].state = ND6_REACHABLE;
+
+      /* Send queued packets, if any. */
+      if (neighbor_cache[i].q != NULL) {
+        nd6_send_q(i);
+      }
+    }
+
+    break; /* ICMP6_TYPE_NA */
+  }
+  case ICMP6_TYPE_NS: /* Neighbor solicitation. */
+  {
+    struct ns_header * ns_hdr;
+    struct lladdr_option * lladdr_opt;
+    u8_t accepted;
+
+    /* Check that ns header fits in packet. */
+    if (p->len < sizeof(struct ns_header)) {
+      /* TODO debug message */
+      pbuf_free(p);
+      ND6_STATS_INC(nd6.lenerr);
+      ND6_STATS_INC(nd6.drop);
+      return;
+    }
+
+    ns_hdr = (struct ns_header *)p->payload;
+
+    /* Check if there is a link-layer address provided. Only point to it if in this buffer. */
+    lladdr_opt = NULL;
+    if (p->len >= (sizeof(struct ns_header) + sizeof(struct lladdr_option))) {
+      lladdr_opt = (struct lladdr_option *)((u8_t*)p->payload + sizeof(struct ns_header));
+    }
+
+    /* Check if the target address is configured on the receiving netif. */
+    accepted = 0;
+    for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; ++i) {
+      if ((ip6_addr_isvalid(netif_ip6_addr_state(inp, i)) ||
+           (ip6_addr_istentative(netif_ip6_addr_state(inp, i)) &&
+            ip6_addr_isany(ip6_current_src_addr()))) &&
+          ip6_addr_cmp(&(ns_hdr->target_address), netif_ip6_addr(inp, i))) {
+        accepted = 1;
+        break;
+      }
+    }
+
+    /* NS not for us? */
+    if (!accepted) {
+      pbuf_free(p);
+      return;
+    }
+
+    /* Check for ANY address in src (DAD algorithm). */
+    if (ip6_addr_isany(ip6_current_src_addr())) {
+      /* Sender is validating this address. */
+      for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; ++i) {
+        if (ip6_addr_cmp(&(ns_hdr->target_address), netif_ip6_addr(inp, i))) {
+          /* Send a NA back so that the sender does not use this address. */
+          nd6_send_na(inp, netif_ip6_addr(inp, i), ND6_FLAG_OVERRIDE | ND6_SEND_FLAG_ALLNODES_DEST);
+          if (ip6_addr_istentative(netif_ip6_addr_state(inp, i))) {
+            /* We shouldn't use this address either. */
+            netif_ip6_addr_set_state(inp, i, IP6_ADDR_INVALID);
+          }
+        }
+      }
+    }
+    else {
+      /* Sender is trying to resolve our address. */
+      /* Verify that they included their own link-layer address. */
+      if (lladdr_opt == NULL) {
+        /* Not a valid message. */
+        pbuf_free(p);
+        ND6_STATS_INC(nd6.proterr);
+        ND6_STATS_INC(nd6.drop);
+        return;
+      }
+
+      i = nd6_find_neighbor_cache_entry(ip6_current_src_addr());
+      if ( i>= 0) {
+        /* We already have a record for the solicitor. */
+        if (neighbor_cache[i].state == ND6_INCOMPLETE) {
+          neighbor_cache[i].netif = inp;
+          MEMCPY(neighbor_cache[i].lladdr, lladdr_opt->addr, inp->hwaddr_len);
+
+          /* Delay probe in case we get confirmation of reachability from upper layer (TCP). */
+          neighbor_cache[i].state = ND6_DELAY;
+          neighbor_cache[i].counter.delay_time = LWIP_ND6_DELAY_FIRST_PROBE_TIME;
+        }
+      }
+      else
+      {
+        /* Add their IPv6 address and link-layer address to neighbor cache.
+         * We will need it at least to send a unicast NA message, but most
+         * likely we will also be communicating with this node soon. */
+        i = nd6_new_neighbor_cache_entry();
+        if (i < 0) {
+          /* We couldn't assign a cache entry for this neighbor.
+           * we won't be able to reply. drop it. */
+          pbuf_free(p);
+          ND6_STATS_INC(nd6.memerr);
+          return;
+        }
+        neighbor_cache[i].netif = inp;
+        MEMCPY(neighbor_cache[i].lladdr, lladdr_opt->addr, inp->hwaddr_len);
+        ip6_addr_set(&(neighbor_cache[i].next_hop_address), ip6_current_src_addr());
+
+        /* Receiving a message does not prove reachability: only in one direction.
+         * Delay probe in case we get confirmation of reachability from upper layer (TCP). */
+        neighbor_cache[i].state = ND6_DELAY;
+        neighbor_cache[i].counter.delay_time = LWIP_ND6_DELAY_FIRST_PROBE_TIME;
+      }
+
+      /* Override ip6_current_dest_addr() so that we have an aligned copy. */
+      ip6_addr_set(ip6_current_dest_addr(), &(ns_hdr->target_address));
+
+      /* Send back a NA for us. Allocate the reply pbuf. */
+      nd6_send_na(inp, ip6_current_dest_addr(), ND6_FLAG_SOLICITED | ND6_FLAG_OVERRIDE);
+    }
+
+    break; /* ICMP6_TYPE_NS */
+  }
+  case ICMP6_TYPE_RA: /* Router Advertisement. */
+  {
+    struct ra_header * ra_hdr;
+    u8_t * buffer; /* Used to copy options. */
+    u16_t offset;
+
+    /* Check that RA header fits in packet. */
+    if (p->len < sizeof(struct ra_header)) {
+      /* TODO debug message */
+      pbuf_free(p);
+      ND6_STATS_INC(nd6.lenerr);
+      ND6_STATS_INC(nd6.drop);
+      return;
+    }
+
+    ra_hdr = (struct ra_header *)p->payload;
+
+    /* If we are sending RS messages, stop. */
+#if LWIP_IPV6_SEND_ROUTER_SOLICIT
+    inp->rs_count = 0;
+#endif /* LWIP_IPV6_SEND_ROUTER_SOLICIT */
+
+    /* Get the matching default router entry. */
+    i = nd6_get_router(ip6_current_src_addr(), inp);
+    if (i < 0) {
+      /* Create a new router entry. */
+      i = nd6_new_router(ip6_current_src_addr(), inp);
+    }
+
+    if (i < 0) {
+      /* Could not create a new router entry. */
+      pbuf_free(p);
+      ND6_STATS_INC(nd6.memerr);
+      return;
+    }
+
+    /* Re-set invalidation timer. */
+    default_router_list[i].invalidation_timer = ra_hdr->router_lifetime;
+
+    /* Re-set default timer values. */
+#if LWIP_ND6_ALLOW_RA_UPDATES
+    if (ra_hdr->retrans_timer > 0) {
+      retrans_timer = ra_hdr->retrans_timer;
+    }
+    if (ra_hdr->reachable_time > 0) {
+      reachable_time = ra_hdr->reachable_time;
+    }
+#endif /* LWIP_ND6_ALLOW_RA_UPDATES */
+
+    /* TODO set default hop limit... */
+    /* ra_hdr->current_hop_limit;*/
+
+    /* Update flags in local entry (incl. preference). */
+    default_router_list[i].flags = ra_hdr->flags;
+
+    /* Offset to options. */
+    offset = sizeof(struct ra_header);
+
+    /* Process each option. */
+    while ((p->tot_len - offset) > 0) {
+      if (p->len == p->tot_len) {
+        /* no need to copy from contiguous pbuf */
+        buffer = &((u8_t*)p->payload)[offset];
+      } else {
+        buffer = nd6_ra_buffer;
+        pbuf_copy_partial(p, buffer, sizeof(struct prefix_option), offset);
+      }
+      switch (buffer[0]) {
+      case ND6_OPTION_TYPE_SOURCE_LLADDR:
+      {
+        struct lladdr_option * lladdr_opt;
+        lladdr_opt = (struct lladdr_option *)buffer;
+        if ((default_router_list[i].neighbor_entry != NULL) &&
+            (default_router_list[i].neighbor_entry->state == ND6_INCOMPLETE)) {
+          SMEMCPY(default_router_list[i].neighbor_entry->lladdr, lladdr_opt->addr, inp->hwaddr_len);
+          default_router_list[i].neighbor_entry->state = ND6_REACHABLE;
+          default_router_list[i].neighbor_entry->counter.reachable_time = reachable_time;
+        }
+        break;
+      }
+      case ND6_OPTION_TYPE_MTU:
+      {
+        struct mtu_option * mtu_opt;
+        mtu_opt = (struct mtu_option *)buffer;
+        if (mtu_opt->mtu >= 1280) {
+#if LWIP_ND6_ALLOW_RA_UPDATES
+          inp->mtu = mtu_opt->mtu;
+#endif /* LWIP_ND6_ALLOW_RA_UPDATES */
+        }
+        break;
+      }
+      case ND6_OPTION_TYPE_PREFIX_INFO:
+      {
+        struct prefix_option * prefix_opt;
+        prefix_opt = (struct prefix_option *)buffer;
+
+        if (prefix_opt->flags & ND6_PREFIX_FLAG_ON_LINK) {
+          /* Add to on-link prefix list. */
+          s8_t prefix;
+
+          /* Get a memory-aligned copy of the prefix. */
+          ip6_addr_set(ip6_current_dest_addr(), &(prefix_opt->prefix));
+
+          /* find cache entry for this prefix. */
+          prefix = nd6_get_onlink_prefix(ip6_current_dest_addr(), inp);
+          if (prefix < 0) {
+            /* Create a new cache entry. */
+            prefix = nd6_new_onlink_prefix(ip6_current_dest_addr(), inp);
+          }
+          if (prefix >= 0) {
+            prefix_list[prefix].invalidation_timer = prefix_opt->valid_lifetime;
+
+#if LWIP_IPV6_AUTOCONFIG
+            if (prefix_opt->flags & ND6_PREFIX_FLAG_AUTONOMOUS) {
+              /* Mark prefix as autonomous, so that address autoconfiguration can take place.
+               * Only OR flag, so that we don't over-write other flags (such as ADDRESS_DUPLICATE)*/
+              prefix_list[prefix].flags |= ND6_PREFIX_AUTOCONFIG_AUTONOMOUS;
+            }
+#endif /* LWIP_IPV6_AUTOCONFIG */
+          }
+        }
+
+        break;
+      }
+      case ND6_OPTION_TYPE_ROUTE_INFO:
+      {
+        /* TODO implement preferred routes.
+        struct route_option * route_opt;
+        route_opt = (struct route_option *)buffer;*/
+
+        break;
+      }
+      default:
+        /* Unrecognized option, abort. */
+        ND6_STATS_INC(nd6.proterr);
+        break;
+      }
+      offset += 8 * ((u16_t)buffer[1]);
+    }
+
+    break; /* ICMP6_TYPE_RA */
+  }
+  case ICMP6_TYPE_RD: /* Redirect */
+  {
+    struct redirect_header * redir_hdr;
+    struct lladdr_option * lladdr_opt;
+
+    /* Check that Redir header fits in packet. */
+    if (p->len < sizeof(struct redirect_header)) {
+      /* TODO debug message */
+      pbuf_free(p);
+      ND6_STATS_INC(nd6.lenerr);
+      ND6_STATS_INC(nd6.drop);
+      return;
+    }
+
+    redir_hdr = (struct redirect_header *)p->payload;
+
+    lladdr_opt = NULL;
+    if (p->len >= (sizeof(struct redirect_header) + sizeof(struct lladdr_option))) {
+      lladdr_opt = (struct lladdr_option *)((u8_t*)p->payload + sizeof(struct redirect_header));
+    }
+
+    /* Copy original destination address to current source address, to have an aligned copy. */
+    ip6_addr_set(ip6_current_src_addr(), &(redir_hdr->destination_address));
+
+    /* Find dest address in cache */
+    i = nd6_find_destination_cache_entry(ip6_current_src_addr());
+    if (i < 0) {
+      /* Destination not in cache, drop packet. */
+      pbuf_free(p);
+      return;
+    }
+
+    /* Set the new target address. */
+    ip6_addr_set(&(destination_cache[i].next_hop_addr), &(redir_hdr->target_address));
+
+    /* If Link-layer address of other router is given, try to add to neighbor cache. */
+    if (lladdr_opt != NULL) {
+      if (lladdr_opt->type == ND6_OPTION_TYPE_TARGET_LLADDR) {
+        /* Copy target address to current source address, to have an aligned copy. */
+        ip6_addr_set(ip6_current_src_addr(), &(redir_hdr->target_address));
+
+        i = nd6_find_neighbor_cache_entry(ip6_current_src_addr());
+        if (i < 0) {
+          i = nd6_new_neighbor_cache_entry();
+          if (i >= 0) {
+            neighbor_cache[i].netif = inp;
+            MEMCPY(neighbor_cache[i].lladdr, lladdr_opt->addr, inp->hwaddr_len);
+            ip6_addr_set(&(neighbor_cache[i].next_hop_address), ip6_current_src_addr());
+
+            /* Receiving a message does not prove reachability: only in one direction.
+             * Delay probe in case we get confirmation of reachability from upper layer (TCP). */
+            neighbor_cache[i].state = ND6_DELAY;
+            neighbor_cache[i].counter.delay_time = LWIP_ND6_DELAY_FIRST_PROBE_TIME;
+          }
+        }
+        if (i >= 0) {
+          if (neighbor_cache[i].state == ND6_INCOMPLETE) {
+            MEMCPY(neighbor_cache[i].lladdr, lladdr_opt->addr, inp->hwaddr_len);
+            /* Receiving a message does not prove reachability: only in one direction.
+             * Delay probe in case we get confirmation of reachability from upper layer (TCP). */
+            neighbor_cache[i].state = ND6_DELAY;
+            neighbor_cache[i].counter.delay_time = LWIP_ND6_DELAY_FIRST_PROBE_TIME;
+          }
+        }
+      }
+    }
+    break; /* ICMP6_TYPE_RD */
+  }
+  case ICMP6_TYPE_PTB: /* Packet too big */
+  {
+    struct icmp6_hdr *icmp6hdr; /* Packet too big message */
+    struct ip6_hdr * ip6hdr; /* IPv6 header of the packet which caused the error */
+
+    /* Check that ICMPv6 header + IPv6 header fit in payload */
+    if (p->len < (sizeof(struct icmp6_hdr) + IP6_HLEN)) {
+      /* drop short packets */
+      pbuf_free(p);
+      ND6_STATS_INC(nd6.lenerr);
+      ND6_STATS_INC(nd6.drop);
+      return;
+    }
+
+    icmp6hdr = (struct icmp6_hdr *)p->payload;
+    ip6hdr = (struct ip6_hdr *)((u8_t*)p->payload + sizeof(struct icmp6_hdr));
+
+    /* Copy original destination address to current source address, to have an aligned copy. */
+    ip6_addr_set(ip6_current_src_addr(), &(ip6hdr->dest));
+
+    /* Look for entry in destination cache. */
+    i = nd6_find_destination_cache_entry(ip6_current_src_addr());
+    if (i < 0) {
+      /* Destination not in cache, drop packet. */
+      pbuf_free(p);
+      return;
+    }
+
+    /* Change the Path MTU. */
+    destination_cache[i].pmtu = icmp6hdr->data;
+
+    break; /* ICMP6_TYPE_PTB */
+  }
+
+  default:
+    ND6_STATS_INC(nd6.proterr);
+    ND6_STATS_INC(nd6.drop);
+    break; /* default */
+  }
+
+  pbuf_free(p);
+}
+
+
+/**
+ * Periodic timer for Neighbor discovery functions:
+ *
+ * - Update neighbor reachability states
+ * - Update destination cache entries age
+ * - Update invalidation timers of default routers and on-link prefixes
+ * - Perform duplicate address detection (DAD) for our addresses
+ * - Send router solicitations
+ */
+void
+nd6_tmr(void)
+{
+  s8_t i, j;
+  struct netif * netif;
+
+  /* Process neighbor entries. */
+  for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++) {
+    switch (neighbor_cache[i].state) {
+    case ND6_INCOMPLETE:
+      if (neighbor_cache[i].counter.probes_sent >= LWIP_ND6_MAX_MULTICAST_SOLICIT) {
+        /* Retries exceeded. */
+        nd6_free_neighbor_cache_entry(i);
+      }
+      else {
+        /* Send a NS for this entry. */
+        neighbor_cache[i].counter.probes_sent++;
+        nd6_send_ns(neighbor_cache[i].netif, &(neighbor_cache[i].next_hop_address), ND6_SEND_FLAG_MULTICAST_DEST);
+      }
+      break;
+    case ND6_REACHABLE:
+      /* Send queued packets, if any are left. Should have been sent already. */
+      if (neighbor_cache[i].q != NULL) {
+        nd6_send_q(i);
+      }
+      if (neighbor_cache[i].counter.reachable_time <= ND6_TMR_INTERVAL) {
+        /* Change to stale state. */
+        neighbor_cache[i].state = ND6_STALE;
+        neighbor_cache[i].counter.stale_time = 0;
+      }
+      else {
+        neighbor_cache[i].counter.reachable_time -= ND6_TMR_INTERVAL;
+      }
+      break;
+    case ND6_STALE:
+      neighbor_cache[i].counter.stale_time += ND6_TMR_INTERVAL;
+      break;
+    case ND6_DELAY:
+      if (neighbor_cache[i].counter.delay_time <= ND6_TMR_INTERVAL) {
+        /* Change to PROBE state. */
+        neighbor_cache[i].state = ND6_PROBE;
+        neighbor_cache[i].counter.probes_sent = 0;
+      }
+      else {
+        neighbor_cache[i].counter.delay_time -= ND6_TMR_INTERVAL;
+      }
+      break;
+    case ND6_PROBE:
+      if (neighbor_cache[i].counter.probes_sent >= LWIP_ND6_MAX_MULTICAST_SOLICIT) {
+        /* Retries exceeded. */
+        nd6_free_neighbor_cache_entry(i);
+      }
+      else {
+        /* Send a NS for this entry. */
+        neighbor_cache[i].counter.probes_sent++;
+        nd6_send_ns(neighbor_cache[i].netif, &(neighbor_cache[i].next_hop_address), 0);
+      }
+      break;
+    case ND6_NO_ENTRY:
+    default:
+      /* Do nothing. */
+      break;
+    }
+  }
+
+  /* Process destination entries. */
+  for (i = 0; i < LWIP_ND6_NUM_DESTINATIONS; i++) {
+    destination_cache[i].age++;
+  }
+
+  /* Process router entries. */
+  for (i = 0; i < LWIP_ND6_NUM_ROUTERS; i++) {
+    if (default_router_list[i].neighbor_entry != NULL) {
+      /* Active entry. */
+      if (default_router_list[i].invalidation_timer > 0) {
+        default_router_list[i].invalidation_timer -= ND6_TMR_INTERVAL / 1000;
+      }
+      if (default_router_list[i].invalidation_timer < ND6_TMR_INTERVAL / 1000) {
+        /* Less than 1 second remainig. Clear this entry. */
+        default_router_list[i].neighbor_entry->isrouter = 0;
+        default_router_list[i].neighbor_entry = NULL;
+        default_router_list[i].invalidation_timer = 0;
+        default_router_list[i].flags = 0;
+      }
+    }
+  }
+
+  /* Process prefix entries. */
+  for (i = 0; i < LWIP_ND6_NUM_PREFIXES; i++) {
+    if (prefix_list[i].invalidation_timer < ND6_TMR_INTERVAL / 1000) {
+      prefix_list[i].invalidation_timer = 0;
+    }
+    if ((prefix_list[i].invalidation_timer > 0) &&
+        (prefix_list[i].netif != NULL)) {
+      prefix_list[i].invalidation_timer -= ND6_TMR_INTERVAL / 1000;
+
+#if LWIP_IPV6_AUTOCONFIG
+      /* Initiate address autoconfiguration for this prefix, if conditions are met. */
+      if (prefix_list[i].netif->ip6_autoconfig_enabled &&
+          (prefix_list[i].flags & ND6_PREFIX_AUTOCONFIG_AUTONOMOUS) &&
+          !(prefix_list[i].flags & ND6_PREFIX_AUTOCONFIG_ADDRESS_GENERATED)) {
+        /* Try to get an address on this netif that is invalid.
+         * Skip 0 index (link-local address) */
+        for (j = 1; j < LWIP_IPV6_NUM_ADDRESSES; j++) {
+          if (netif_ip6_addr_state(prefix_list[i].netif, j) == IP6_ADDR_INVALID) {
+            /* Generate an address using this prefix and interface ID from link-local address. */
+            prefix_list[i].netif->ip6_addr[j].addr[0] = prefix_list[i].prefix.addr[0];
+            prefix_list[i].netif->ip6_addr[j].addr[1] = prefix_list[i].prefix.addr[1];
+            prefix_list[i].netif->ip6_addr[j].addr[2] = prefix_list[i].netif->ip6_addr[0].addr[2];
+            prefix_list[i].netif->ip6_addr[j].addr[3] = prefix_list[i].netif->ip6_addr[0].addr[3];
+
+            /* Mark it as tentative (DAD will be performed if configured). */
+            netif_ip6_addr_set_state(prefix_list[i].netif, j, IP6_ADDR_TENTATIVE);
+
+            /* Mark this prefix with ADDRESS_GENERATED, so that we don't try again. */
+            prefix_list[i].flags |= ND6_PREFIX_AUTOCONFIG_ADDRESS_GENERATED;
+
+            /* Exit loop. */
+            break;
+          }
+        }
+      }
+#endif /* LWIP_IPV6_AUTOCONFIG */
+    }
+  }
+
+
+  /* Process our own addresses, if DAD configured. */
+  for (netif = netif_list; netif != NULL; netif = netif->next) {
+    for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; ++i) {
+      if (ip6_addr_istentative(netif->ip6_addr_state[i])) {
+        if ((netif->ip6_addr_state[i] & 0x07) >= LWIP_IPV6_DUP_DETECT_ATTEMPTS) {
+          /* No NA received in response. Mark address as valid. */
+          netif->ip6_addr_state[i] = IP6_ADDR_PREFERRED;
+          /* TODO implement preferred and valid lifetimes. */
+        }
+        else if (netif->flags & NETIF_FLAG_UP) {
+#if LWIP_IPV6_MLD
+          if ((netif->ip6_addr_state[i] & 0x07) == 0) {
+            /* Join solicited node multicast group. */
+            ip6_addr_set_solicitednode(&multicast_address, netif_ip6_addr(netif, i)->addr[3]);
+            mld6_joingroup(netif_ip6_addr(netif, i), &multicast_address);
+          }
+#endif /* LWIP_IPV6_MLD */
+          /* Send a NS for this address. */
+          nd6_send_ns(netif, netif_ip6_addr(netif, i), ND6_SEND_FLAG_MULTICAST_DEST);
+          (netif->ip6_addr_state[i])++;
+          /* TODO send max 1 NS per tmr call? enable return*/
+          /*return;*/
+        }
+      }
+    }
+  }
+
+#if LWIP_IPV6_SEND_ROUTER_SOLICIT
+  /* Send router solicitation messages, if necessary. */
+  for (netif = netif_list; netif != NULL; netif = netif->next) {
+    if ((netif->rs_count > 0) && (netif->flags & NETIF_FLAG_UP)) {
+      nd6_send_rs(netif);
+      netif->rs_count--;
+    }
+  }
+#endif /* LWIP_IPV6_SEND_ROUTER_SOLICIT */
+
+}
+
+/**
+ * Send a neighbor solicitation message
+ *
+ * @param netif the netif on which to send the message
+ * @param target_addr the IPv6 target address for the ND message
+ * @param flags one of ND6_SEND_FLAG_*
+ */
+static void
+nd6_send_ns(struct netif * netif, ip6_addr_t * target_addr, u8_t flags)
+{
+  struct ns_header * ns_hdr;
+  struct lladdr_option * lladdr_opt;
+  struct pbuf * p;
+  ip6_addr_t * src_addr;
+
+  if (ip6_addr_isvalid(netif_ip6_addr_state(netif,0))) {
+    /* Use link-local address as source address. */
+    src_addr = netif_ip6_addr(netif, 0);
+  } else {
+    src_addr = IP6_ADDR_ANY;
+  }
+
+  /* Allocate a packet. */
+  p = pbuf_alloc(PBUF_IP, sizeof(struct ns_header) + sizeof(struct lladdr_option), PBUF_RAM);
+  if ((p == NULL) || (p->len < (sizeof(struct ns_header) + sizeof(struct lladdr_option)))) {
+    /* We couldn't allocate a suitable pbuf for the ns. drop it. */
+    if (p != NULL) {
+      pbuf_free(p);
+    }
+    ND6_STATS_INC(nd6.memerr);
+    return;
+  }
+
+  /* Set fields. */
+  ns_hdr = (struct ns_header *)p->payload;
+  lladdr_opt = (struct lladdr_option *)((u8_t*)p->payload + sizeof(struct ns_header));
+
+  ns_hdr->type = ICMP6_TYPE_NS;
+  ns_hdr->code = 0;
+  ns_hdr->chksum = 0;
+  ns_hdr->reserved = 0;
+  ip6_addr_set(&(ns_hdr->target_address), target_addr);
+
+  lladdr_opt->type = ND6_OPTION_TYPE_SOURCE_LLADDR;
+  lladdr_opt->length = ((netif->hwaddr_len + 2) >> 3) + (((netif->hwaddr_len + 2) & 0x07) ? 1 : 0);
+  SMEMCPY(lladdr_opt->addr, netif->hwaddr, netif->hwaddr_len);
+
+  /* Generate the solicited node address for the target address. */
+  if (flags & ND6_SEND_FLAG_MULTICAST_DEST) {
+    ip6_addr_set_solicitednode(&multicast_address, target_addr->addr[3]);
+    target_addr = &multicast_address;
+  }
+
+#if CHECKSUM_GEN_ICMP6
+  ns_hdr->chksum = ip6_chksum_pseudo(p, IP6_NEXTH_ICMP6, p->len, src_addr,
+    target_addr);
+#endif /* CHECKSUM_GEN_ICMP6 */
+
+  /* Send the packet out. */
+  ND6_STATS_INC(nd6.xmit);
+  ip6_output_if(p, (src_addr == IP6_ADDR_ANY) ? NULL : src_addr, target_addr,
+      LWIP_ICMP6_HL, 0, IP6_NEXTH_ICMP6, netif);
+  pbuf_free(p);
+}
+
+/**
+ * Send a neighbor advertisement message
+ *
+ * @param netif the netif on which to send the message
+ * @param target_addr the IPv6 target address for the ND message
+ * @param flags one of ND6_SEND_FLAG_*
+ */
+static void
+nd6_send_na(struct netif * netif, ip6_addr_t * target_addr, u8_t flags)
+{
+  struct na_header * na_hdr;
+  struct lladdr_option * lladdr_opt;
+  struct pbuf * p;
+  ip6_addr_t * src_addr;
+  ip6_addr_t * dest_addr;
+
+  /* Use link-local address as source address. */
+  /* src_addr = &(netif->ip6_addr[0]); */
+  /* Use target address as source address. */
+  src_addr = target_addr;
+
+  /* Allocate a packet. */
+  p = pbuf_alloc(PBUF_IP, sizeof(struct na_header) + sizeof(struct lladdr_option), PBUF_RAM);
+  if ((p == NULL) || (p->len < (sizeof(struct na_header) + sizeof(struct lladdr_option)))) {
+    /* We couldn't allocate a suitable pbuf for the ns. drop it. */
+    if (p != NULL) {
+      pbuf_free(p);
+    }
+    ND6_STATS_INC(nd6.memerr);
+    return;
+  }
+
+  /* Set fields. */
+  na_hdr = (struct na_header *)p->payload;
+  lladdr_opt = (struct lladdr_option *)((u8_t*)p->payload + sizeof(struct na_header));
+
+  na_hdr->type = ICMP6_TYPE_NA;
+  na_hdr->code = 0;
+  na_hdr->chksum = 0;
+  na_hdr->flags = flags & 0xf0;
+  na_hdr->reserved[0] = 0;
+  na_hdr->reserved[1] = 0;
+  na_hdr->reserved[2] = 0;
+  ip6_addr_set(&(na_hdr->target_address), target_addr);
+
+  lladdr_opt->type = ND6_OPTION_TYPE_TARGET_LLADDR;
+  lladdr_opt->length = ((netif->hwaddr_len + 2) >> 3) + (((netif->hwaddr_len + 2) & 0x07) ? 1 : 0);
+  SMEMCPY(lladdr_opt->addr, netif->hwaddr, netif->hwaddr_len);
+
+  /* Generate the solicited node address for the target address. */
+  if (flags & ND6_SEND_FLAG_MULTICAST_DEST) {
+    ip6_addr_set_solicitednode(&multicast_address, target_addr->addr[3]);
+    dest_addr = &multicast_address;
+  }
+  else if (flags & ND6_SEND_FLAG_ALLNODES_DEST) {
+    ip6_addr_set_allnodes_linklocal(&multicast_address);
+    dest_addr = &multicast_address;
+  }
+  else {
+    dest_addr = ip6_current_src_addr();
+  }
+
+#if CHECKSUM_GEN_ICMP6
+  na_hdr->chksum = ip6_chksum_pseudo(p, IP6_NEXTH_ICMP6, p->len, src_addr,
+    dest_addr);
+#endif /* CHECKSUM_GEN_ICMP6 */
+
+  /* Send the packet out. */
+  ND6_STATS_INC(nd6.xmit);
+  ip6_output_if(p, src_addr, dest_addr,
+      LWIP_ICMP6_HL, 0, IP6_NEXTH_ICMP6, netif);
+  pbuf_free(p);
+}
+
+#if LWIP_IPV6_SEND_ROUTER_SOLICIT
+/**
+ * Send a router solicitation message
+ *
+ * @param netif the netif on which to send the message
+ */
+static void
+nd6_send_rs(struct netif * netif)
+{
+  struct rs_header * rs_hdr;
+  struct lladdr_option * lladdr_opt;
+  struct pbuf * p;
+  ip6_addr_t * src_addr;
+  u16_t packet_len;
+
+  /* Link-local source address, or unspecified address? */
+  if (ip6_addr_isvalid(netif_ip6_addr_state(netif, 0))) {
+    src_addr = netif_ip6_addr(netif, 0);
+  }
+  else {
+    src_addr = IP6_ADDR_ANY;
+  }
+
+  /* Generate the all routers target address. */
+  ip6_addr_set_allrouters_linklocal(&multicast_address);
+
+  /* Allocate a packet. */
+  packet_len = sizeof(struct rs_header);
+  if (src_addr != IP6_ADDR_ANY) {
+    packet_len += sizeof(struct lladdr_option);
+  }
+  p = pbuf_alloc(PBUF_IP, packet_len, PBUF_RAM);
+  if ((p == NULL) || (p->len < packet_len)) {
+    /* We couldn't allocate a suitable pbuf for the ns. drop it. */
+    if (p != NULL) {
+      pbuf_free(p);
+    }
+    ND6_STATS_INC(nd6.memerr);
+    return;
+  }
+
+  /* Set fields. */
+  rs_hdr = (struct rs_header *)p->payload;
+
+  rs_hdr->type = ICMP6_TYPE_RS;
+  rs_hdr->code = 0;
+  rs_hdr->chksum = 0;
+  rs_hdr->reserved = 0;
+
+  if (src_addr != IP6_ADDR_ANY) {
+    /* Include our hw address. */
+    lladdr_opt = (struct lladdr_option *)((u8_t*)p->payload + sizeof(struct rs_header));
+    lladdr_opt->type = ND6_OPTION_TYPE_SOURCE_LLADDR;
+    lladdr_opt->length = ((netif->hwaddr_len + 2) >> 3) + (((netif->hwaddr_len + 2) & 0x07) ? 1 : 0);
+    SMEMCPY(lladdr_opt->addr, netif->hwaddr, netif->hwaddr_len);
+  }
+
+#if CHECKSUM_GEN_ICMP6
+  rs_hdr->chksum = ip6_chksum_pseudo(p, IP6_NEXTH_ICMP6, p->len, src_addr,
+    &multicast_address);
+#endif /* CHECKSUM_GEN_ICMP6 */
+
+  /* Send the packet out. */
+  ND6_STATS_INC(nd6.xmit);
+  ip6_output_if(p, src_addr, &multicast_address,
+      LWIP_ICMP6_HL, 0, IP6_NEXTH_ICMP6, netif);
+  pbuf_free(p);
+}
+#endif /* LWIP_IPV6_SEND_ROUTER_SOLICIT */
+
+/**
+ * Search for a neighbor cache entry
+ *
+ * @param ip6addr the IPv6 address of the neighbor
+ * @return The neighbor cache entry index that matched, -1 if no
+ * entry is found
+ */
+static s8_t
+nd6_find_neighbor_cache_entry(ip6_addr_t * ip6addr)
+{
+  s8_t i;
+  for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++) {
+    if (ip6_addr_cmp(ip6addr, &(neighbor_cache[i].next_hop_address))) {
+      return i;
+    }
+  }
+  return -1;
+}
+
+/**
+ * Create a new neighbor cache entry.
+ *
+ * If no unused entry is found, will try to recycle an old entry
+ * according to ad-hoc "age" heuristic.
+ *
+ * @return The neighbor cache entry index that was created, -1 if no
+ * entry could be created
+ */
+static s8_t
+nd6_new_neighbor_cache_entry(void)
+{
+  s8_t i;
+  s8_t j;
+  u32_t time;
+
+
+  /* First, try to find an empty entry. */
+  for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++) {
+    if (neighbor_cache[i].state == ND6_NO_ENTRY) {
+      return i;
+    }
+  }
+
+  /* We need to recycle an entry. in general, do not recycle if it is a router. */
+
+  /* Next, try to find a Stale entry. */
+  for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++) {
+    if ((neighbor_cache[i].state == ND6_STALE) &&
+        (!neighbor_cache[i].isrouter)) {
+      nd6_free_neighbor_cache_entry(i);
+      return i;
+    }
+  }
+
+  /* Next, try to find a Probe entry. */
+  for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++) {
+    if ((neighbor_cache[i].state == ND6_PROBE) &&
+        (!neighbor_cache[i].isrouter)) {
+      nd6_free_neighbor_cache_entry(i);
+      return i;
+    }
+  }
+
+  /* Next, try to find a Delayed entry. */
+  for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++) {
+    if ((neighbor_cache[i].state == ND6_DELAY) &&
+        (!neighbor_cache[i].isrouter)) {
+      nd6_free_neighbor_cache_entry(i);
+      return i;
+    }
+  }
+
+  /* Next, try to find the oldest reachable entry. */
+  time = 0xfffffffful;
+  j = -1;
+  for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++) {
+    if ((neighbor_cache[i].state == ND6_REACHABLE) &&
+        (!neighbor_cache[i].isrouter)) {
+      if (neighbor_cache[i].counter.reachable_time < time) {
+        j = i;
+        time = neighbor_cache[i].counter.reachable_time;
+      }
+    }
+  }
+  if (j >= 0) {
+    nd6_free_neighbor_cache_entry(j);
+    return j;
+  }
+
+  /* Next, find oldest incomplete entry without queued packets. */
+  time = 0;
+  j = -1;
+  for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++) {
+    if (
+        (neighbor_cache[i].q == NULL) &&
+        (neighbor_cache[i].state == ND6_INCOMPLETE) &&
+        (!neighbor_cache[i].isrouter)) {
+      if (neighbor_cache[i].counter.probes_sent >= time) {
+        j = i;
+        time = neighbor_cache[i].counter.probes_sent;
+      }
+    }
+  }
+  if (j >= 0) {
+    nd6_free_neighbor_cache_entry(j);
+    return j;
+  }
+
+  /* Next, find oldest incomplete entry with queued packets. */
+  time = 0;
+  j = -1;
+  for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++) {
+    if ((neighbor_cache[i].state == ND6_INCOMPLETE) &&
+        (!neighbor_cache[i].isrouter)) {
+      if (neighbor_cache[i].counter.probes_sent >= time) {
+        j = i;
+        time = neighbor_cache[i].counter.probes_sent;
+      }
+    }
+  }
+  if (j >= 0) {
+    nd6_free_neighbor_cache_entry(j);
+    return j;
+  }
+
+  /* No more entries to try. */
+  return -1;
+}
+
+/**
+ * Will free any resources associated with a neighbor cache
+ * entry, and will mark it as unused.
+ *
+ * @param i the neighbor cache entry index to free
+ */
+static void
+nd6_free_neighbor_cache_entry(s8_t i)
+{
+  if ((i < 0) || (i >= LWIP_ND6_NUM_NEIGHBORS)) {
+    return;
+  }
+
+  /* Free any queued packets. */
+  if (neighbor_cache[i].q != NULL) {
+    nd6_free_q(neighbor_cache[i].q);
+    neighbor_cache[i].q = NULL;
+  }
+
+  neighbor_cache[i].state = ND6_NO_ENTRY;
+  neighbor_cache[i].isrouter = 0;
+  neighbor_cache[i].netif = NULL;
+  neighbor_cache[i].counter.reachable_time = 0;
+  ip6_addr_set_zero(&(neighbor_cache[i].next_hop_address));
+}
+
+/**
+ * Search for a destination cache entry
+ *
+ * @param ip6addr the IPv6 address of the destination
+ * @return The destination cache entry index that matched, -1 if no
+ * entry is found
+ */
+static s8_t
+nd6_find_destination_cache_entry(ip6_addr_t * ip6addr)
+{
+  s8_t i;
+  for (i = 0; i < LWIP_ND6_NUM_DESTINATIONS; i++) {
+    if (ip6_addr_cmp(ip6addr, &(destination_cache[i].destination_addr))) {
+      return i;
+    }
+  }
+  return -1;
+}
+
+/**
+ * Create a new destination cache entry. If no unused entry is found,
+ * will recycle oldest entry.
+ *
+ * @return The destination cache entry index that was created, -1 if no
+ * entry was created
+ */
+static s8_t
+nd6_new_destination_cache_entry(void)
+{
+  s8_t i, j;
+  u32_t age;
+
+  /* Find an empty entry. */
+  for (i = 0; i < LWIP_ND6_NUM_DESTINATIONS; i++) {
+    if (ip6_addr_isany(&(destination_cache[i].destination_addr))) {
+      return i;
+    }
+  }
+
+  /* Find oldest entry. */
+  age = 0;
+  j = LWIP_ND6_NUM_DESTINATIONS - 1;
+  for (i = 0; i < LWIP_ND6_NUM_DESTINATIONS; i++) {
+    if (destination_cache[i].age > age) {
+      j = i;
+    }
+  }
+
+  return j;
+}
+
+/**
+ * Determine whether an address matches an on-link prefix.
+ *
+ * @param ip6addr the IPv6 address to match
+ * @return 1 if the address is on-link, 0 otherwise
+ */
+static s8_t
+nd6_is_prefix_in_netif(ip6_addr_t * ip6addr, struct netif * netif)
+{
+  s8_t i;
+  for (i = 0; i < LWIP_ND6_NUM_PREFIXES; i++) {
+    if ((prefix_list[i].netif == netif) &&
+        (prefix_list[i].invalidation_timer > 0) &&
+        ip6_addr_netcmp(ip6addr, &(prefix_list[i].prefix))) {
+      return 1;
+    }
+  }
+  /* Check to see if address prefix matches a (manually?) configured address. */
+  for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; i++) {
+    if (ip6_addr_isvalid(netif_ip6_addr_state(netif, i)) &&
+        ip6_addr_netcmp(ip6addr, netif_ip6_addr(netif, i))) {
+      return 1;
+    }
+  }
+  return 0;
+}
+
+/**
+ * Select a default router for a destination.
+ *
+ * @param ip6addr the destination address
+ * @param netif the netif for the outgoing packet, if known
+ * @return the default router entry index, or -1 if no suitable
+ *         router is found
+ */
+s8_t
+nd6_select_router(ip6_addr_t * ip6addr, struct netif * netif)
+{
+  s8_t i;
+  /* last_router is used for round-robin router selection (as recommended
+   * in RFC). This is more robust in case one router is not reachable,
+   * we are not stuck trying to resolve it. */
+  static s8_t last_router;
+  (void)ip6addr; /* TODO match preferred routes!! (must implement ND6_OPTION_TYPE_ROUTE_INFO) */
+
+  /* TODO: implement default router preference */
+
+  /* Look for reachable routers. */
+  for (i = 0; i < LWIP_ND6_NUM_ROUTERS; i++) {
+    if (++last_router >= LWIP_ND6_NUM_ROUTERS) {
+      last_router = 0;
+    }
+    if ((default_router_list[i].neighbor_entry != NULL) &&
+        (netif != NULL ? netif == default_router_list[i].neighbor_entry->netif : 1) &&
+        (default_router_list[i].invalidation_timer > 0) &&
+        (default_router_list[i].neighbor_entry->state == ND6_REACHABLE)) {
+      return i;
+    }
+  }
+
+  /* Look for router in other reachability states, but still valid according to timer. */
+  for (i = 0; i < LWIP_ND6_NUM_ROUTERS; i++) {
+    if (++last_router >= LWIP_ND6_NUM_ROUTERS) {
+      last_router = 0;
+    }
+    if ((default_router_list[i].neighbor_entry != NULL) &&
+        (netif != NULL ? netif == default_router_list[i].neighbor_entry->netif : 1) &&
+        (default_router_list[i].invalidation_timer > 0)) {
+      return i;
+    }
+  }
+
+  /* Look for any router for which we have any information at all. */
+  for (i = 0; i < LWIP_ND6_NUM_ROUTERS; i++) {
+    if (++last_router >= LWIP_ND6_NUM_ROUTERS) {
+      last_router = 0;
+    }
+    if (default_router_list[i].neighbor_entry != NULL &&
+        (netif != NULL ? netif == default_router_list[i].neighbor_entry->netif : 1)) {
+      return i;
+    }
+  }
+
+  /* no suitable router found. */
+  return -1;
+}
+
+/**
+ * Find an entry for a default router.
+ *
+ * @param router_addr the IPv6 address of the router
+ * @param netif the netif on which the router is found, if known
+ * @return the index of the router entry, or -1 if not found
+ */
+static s8_t
+nd6_get_router(ip6_addr_t * router_addr, struct netif * netif)
+{
+  s8_t i;
+
+  /* Look for router. */
+  for (i = 0; i < LWIP_ND6_NUM_ROUTERS; i++) {
+    if ((default_router_list[i].neighbor_entry != NULL) &&
+        ((netif != NULL) ? netif == default_router_list[i].neighbor_entry->netif : 1) &&
+        ip6_addr_cmp(router_addr, &(default_router_list[i].neighbor_entry->next_hop_address))) {
+      return i;
+    }
+  }
+
+  /* router not found. */
+  return -1;
+}
+
+/**
+ * Create a new entry for a default router.
+ *
+ * @param router_addr the IPv6 address of the router
+ * @param netif the netif on which the router is connected, if known
+ * @return the index on the router table, or -1 if could not be created
+ */
+static s8_t
+nd6_new_router(ip6_addr_t * router_addr, struct netif * netif)
+{
+  s8_t router_index;
+  s8_t neighbor_index;
+
+  /* Do we have a neighbor entry for this router? */
+  neighbor_index = nd6_find_neighbor_cache_entry(router_addr);
+  if (neighbor_index < 0) {
+    /* Create a neighbor entry for this router. */
+    neighbor_index = nd6_new_neighbor_cache_entry();
+    if (neighbor_index < 0) {
+      /* Could not create neighbor entry for this router. */
+      return -1;
+    }
+    ip6_addr_set(&(neighbor_cache[neighbor_index].next_hop_address), router_addr);
+    neighbor_cache[neighbor_index].netif = netif;
+    neighbor_cache[neighbor_index].q = NULL;
+    neighbor_cache[neighbor_index].state = ND6_INCOMPLETE;
+    neighbor_cache[neighbor_index].counter.probes_sent = 0;
+  }
+
+  /* Mark neighbor as router. */
+  neighbor_cache[neighbor_index].isrouter = 1;
+
+  /* Look for empty entry. */
+  for (router_index = 0; router_index < LWIP_ND6_NUM_ROUTERS; router_index++) {
+    if (default_router_list[router_index].neighbor_entry == NULL) {
+      default_router_list[router_index].neighbor_entry = &(neighbor_cache[neighbor_index]);
+      return router_index;
+    }
+  }
+
+  /* Could not create a router entry. */
+
+  /* Mark neighbor entry as not-router. Entry might be useful as neighbor still. */
+  neighbor_cache[neighbor_index].isrouter = 0;
+
+  /* router not found. */
+  return -1;
+}
+
+/**
+ * Find the cached entry for an on-link prefix.
+ *
+ * @param prefix the IPv6 prefix that is on-link
+ * @param netif the netif on which the prefix is on-link
+ * @return the index on the prefix table, or -1 if not found
+ */
+static s8_t
+nd6_get_onlink_prefix(ip6_addr_t * prefix, struct netif * netif)
+{
+  s8_t i;
+
+  /* Look for prefix in list. */
+  for (i = 0; i < LWIP_ND6_NUM_PREFIXES; ++i) {
+    if ((ip6_addr_netcmp(&(prefix_list[i].prefix), prefix)) &&
+        (prefix_list[i].netif == netif)) {
+      return i;
+    }
+  }
+
+  /* Entry not available. */
+  return -1;
+}
+
+/**
+ * Creates a new entry for an on-link prefix.
+ *
+ * @param prefix the IPv6 prefix that is on-link
+ * @param netif the netif on which the prefix is on-link
+ * @return the index on the prefix table, or -1 if not created
+ */
+static s8_t
+nd6_new_onlink_prefix(ip6_addr_t * prefix, struct netif * netif)
+{
+  s8_t i;
+
+  /* Create new entry. */
+  for (i = 0; i < LWIP_ND6_NUM_PREFIXES; ++i) {
+    if ((prefix_list[i].netif == NULL) ||
+        (prefix_list[i].invalidation_timer == 0)) {
+      /* Found empty prefix entry. */
+      prefix_list[i].netif = netif;
+      ip6_addr_set(&(prefix_list[i].prefix), prefix);
+      prefix_list[i].flags = 0;
+      return i;
+    }
+  }
+
+  /* Entry not available. */
+  return -1;
+}
+
+/**
+ * Determine the next hop for a destination. Will determine if the
+ * destination is on-link, else a suitable on-link router is selected.
+ *
+ * The last entry index is cached for fast entry search.
+ *
+ * @param ip6addr the destination address
+ * @param netif the netif on which the packet will be sent
+ * @return the neighbor cache entry for the next hop, ERR_RTE if no
+ *         suitable next hop was found, ERR_MEM if no cache entry
+ *         could be created
+ */
+s8_t
+nd6_get_next_hop_entry(ip6_addr_t * ip6addr, struct netif * netif)
+{
+  s8_t i;
+
+#if LWIP_NETIF_HWADDRHINT
+  if (netif->addr_hint != NULL) {
+    /* per-pcb cached entry was given */
+    u8_t addr_hint = *(netif->addr_hint);
+    if (addr_hint < LWIP_ND6_NUM_DESTINATIONS) {
+      nd6_cached_destination_index = addr_hint;
+    }
+  }
+#endif /* LWIP_NETIF_HWADDRHINT */
+
+  /* Look for ip6addr in destination cache. */
+  if (ip6_addr_cmp(ip6addr, &(destination_cache[nd6_cached_destination_index].destination_addr))) {
+    /* the cached entry index is the right one! */
+    /* do nothing. */
+    ND6_STATS_INC(nd6.cachehit);
+  } else {
+    /* Search destination cache. */
+    i = nd6_find_destination_cache_entry(ip6addr);
+    if (i >= 0) {
+      /* found destination entry. make it our new cached index. */
+      nd6_cached_destination_index = i;
+    }
+    else {
+      /* Not found. Create a new destination entry. */
+      i = nd6_new_destination_cache_entry();
+      if (i >= 0) {
+        /* got new destination entry. make it our new cached index. */
+        nd6_cached_destination_index = i;
+      } else {
+        /* Could not create a destination cache entry. */
+        return ERR_MEM;
+      }
+
+      /* Copy dest address to destination cache. */
+      ip6_addr_set(&(destination_cache[nd6_cached_destination_index].destination_addr), ip6addr);
+
+      /* Now find the next hop. is it a neighbor? */
+      if (ip6_addr_islinklocal(ip6addr) ||
+          nd6_is_prefix_in_netif(ip6addr, netif)) {
+        /* Destination in local link. */
+        destination_cache[nd6_cached_destination_index].pmtu = netif->mtu;
+        ip6_addr_copy(destination_cache[nd6_cached_destination_index].next_hop_addr, destination_cache[nd6_cached_destination_index].destination_addr);
+      }
+      else {
+        /* We need to select a router. */
+        i = nd6_select_router(ip6addr, netif);
+        if (i < 0) {
+          /* No router found. */
+          ip6_addr_set_any(&(destination_cache[nd6_cached_destination_index].destination_addr));
+          return ERR_RTE;
+        }
+        destination_cache[nd6_cached_destination_index].pmtu = netif->mtu; /* Start with netif mtu, correct through ICMPv6 if necessary */
+        ip6_addr_copy(destination_cache[nd6_cached_destination_index].next_hop_addr, default_router_list[i].neighbor_entry->next_hop_address);
+      }
+    }
+  }
+
+#if LWIP_NETIF_HWADDRHINT
+  if (netif->addr_hint != NULL) {
+    /* per-pcb cached entry was given */
+    *(netif->addr_hint) = nd6_cached_destination_index;
+  }
+#endif /* LWIP_NETIF_HWADDRHINT */
+
+  /* Look in neighbor cache for the next-hop address. */
+  if (ip6_addr_cmp(&(destination_cache[nd6_cached_destination_index].next_hop_addr),
+                   &(neighbor_cache[nd6_cached_neighbor_index].next_hop_address))) {
+    /* Cache hit. */
+    /* Do nothing. */
+    ND6_STATS_INC(nd6.cachehit);
+  } else {
+    i = nd6_find_neighbor_cache_entry(&(destination_cache[nd6_cached_destination_index].next_hop_addr));
+    if (i >= 0) {
+      /* Found a matching record, make it new cached entry. */
+      nd6_cached_neighbor_index = i;
+    }
+    else {
+      /* Neighbor not in cache. Make a new entry. */
+      i = nd6_new_neighbor_cache_entry();
+      if (i >= 0) {
+        /* got new neighbor entry. make it our new cached index. */
+        nd6_cached_neighbor_index = i;
+      } else {
+        /* Could not create a neighbor cache entry. */
+        return ERR_MEM;
+      }
+
+      /* Initialize fields. */
+      ip6_addr_copy(neighbor_cache[i].next_hop_address,
+                   destination_cache[nd6_cached_destination_index].next_hop_addr);
+      neighbor_cache[i].isrouter = 0;
+      neighbor_cache[i].netif = netif;
+      neighbor_cache[i].state = ND6_INCOMPLETE;
+      neighbor_cache[i].counter.probes_sent = 0;
+    }
+  }
+
+  /* Reset this destination's age. */
+  destination_cache[nd6_cached_destination_index].age = 0;
+
+  return nd6_cached_neighbor_index;
+}
+
+/**
+ * Queue a packet for a neighbor.
+ *
+ * @param neighbor_index the index in the neighbor cache table
+ * @param q packet to be queued
+ * @return ERR_OK if succeeded, ERR_MEM if out of memory
+ */
+err_t
+nd6_queue_packet(s8_t neighbor_index, struct pbuf * q)
+{
+  err_t result = ERR_MEM;
+  struct pbuf *p;
+  int copy_needed = 0;
+#if LWIP_ND6_QUEUEING
+  struct nd6_q_entry *new_entry, *r;
+#endif /* LWIP_ND6_QUEUEING */
+
+  if ((neighbor_index < 0) || (neighbor_index >= LWIP_ND6_NUM_NEIGHBORS)) {
+    return ERR_ARG;
+  }
+
+  /* IF q includes a PBUF_REF, PBUF_POOL or PBUF_RAM, we have no choice but
+   * to copy the whole queue into a new PBUF_RAM (see bug #11400)
+   * PBUF_ROMs can be left as they are, since ROM must not get changed. */
+  p = q;
+  while (p) {
+    if(p->type != PBUF_ROM) {
+      copy_needed = 1;
+      break;
+    }
+    p = p->next;
+  }
+  if(copy_needed) {
+    /* copy the whole packet into new pbufs */
+    p = pbuf_alloc(PBUF_LINK, q->tot_len, PBUF_RAM);
+    while ((p == NULL) && (neighbor_cache[neighbor_index].q != NULL)) {
+      /* Free oldest packet (as per RFC recommendation) */
+#if LWIP_ND6_QUEUEING
+      r = neighbor_cache[neighbor_index].q;
+      neighbor_cache[neighbor_index].q = r->next;
+      r->next = NULL;
+      nd6_free_q(r);
+#else /* LWIP_ND6_QUEUEING */
+      pbuf_free(neighbor_cache[neighbor_index].q);
+      neighbor_cache[neighbor_index].q = NULL;
+#endif /* LWIP_ND6_QUEUEING */
+      p = pbuf_alloc(PBUF_LINK, q->tot_len, PBUF_RAM);
+    }
+    if(p != NULL) {
+      if (pbuf_copy(p, q) != ERR_OK) {
+        pbuf_free(p);
+        p = NULL;
+      }
+    }
+  } else {
+    /* referencing the old pbuf is enough */
+    p = q;
+    pbuf_ref(p);
+  }
+  /* packet was copied/ref'd? */
+  if (p != NULL) {
+    /* queue packet ... */
+#if LWIP_ND6_QUEUEING
+    /* allocate a new nd6 queue entry */
+    new_entry = (struct nd6_q_entry *)memp_malloc(MEMP_ND6_QUEUE);
+    if ((new_entry == NULL) && (neighbor_cache[neighbor_index].q != NULL)) {
+      /* Free oldest packet (as per RFC recommendation) */
+      r = neighbor_cache[neighbor_index].q;
+      neighbor_cache[neighbor_index].q = r->next;
+      r->next = NULL;
+      nd6_free_q(r);
+      new_entry = (struct nd6_q_entry *)memp_malloc(MEMP_ND6_QUEUE);
+    }
+    if (new_entry != NULL) {
+      new_entry->next = NULL;
+      new_entry->p = p;
+      if(neighbor_cache[neighbor_index].q != NULL) {
+        /* queue was already existent, append the new entry to the end */
+        r = neighbor_cache[neighbor_index].q;
+        while (r->next != NULL) {
+          r = r->next;
+        }
+        r->next = new_entry;
+      } else {
+        /* queue did not exist, first item in queue */
+        neighbor_cache[neighbor_index].q = new_entry;
+      }
+      LWIP_DEBUGF(LWIP_DBG_TRACE, ("ipv6: queued packet %p on neighbor entry %"S16_F"\n", (void *)p, (s16_t)neighbor_index));
+      result = ERR_OK;
+    } else {
+      /* the pool MEMP_ND6_QUEUE is empty */
+      pbuf_free(p);
+      LWIP_DEBUGF(LWIP_DBG_TRACE, ("ipv6: could not queue a copy of packet %p (out of memory)\n", (void *)p));
+      /* { result == ERR_MEM } through initialization */
+    }
+#else /* LWIP_ND6_QUEUEING */
+    /* Queue a single packet. If an older packet is already queued, free it as per RFC. */
+    if (neighbor_cache[neighbor_index].q != NULL) {
+      pbuf_free(neighbor_cache[neighbor_index].q);
+    }
+    neighbor_cache[neighbor_index].q = p;
+    LWIP_DEBUGF(LWIP_DBG_TRACE, ("ipv6: queued packet %p on neighbor entry %"S16_F"\n", (void *)p, (s16_t)neighbor_index));
+    result = ERR_OK;
+#endif /* LWIP_ND6_QUEUEING */
+  } else {
+    LWIP_DEBUGF(LWIP_DBG_TRACE, ("ipv6: could not queue a copy of packet %p (out of memory)\n", (void *)q));
+    /* { result == ERR_MEM } through initialization */
+  }
+
+  return result;
+}
+
+#if LWIP_ND6_QUEUEING
+/**
+ * Free a complete queue of nd6 q entries
+ *
+ * @param q a queue of nd6_q_entry to free
+ */
+static void
+nd6_free_q(struct nd6_q_entry *q)
+{
+  struct nd6_q_entry *r;
+  LWIP_ASSERT("q != NULL", q != NULL);
+  LWIP_ASSERT("q->p != NULL", q->p != NULL);
+  while (q) {
+    r = q;
+    q = q->next;
+    LWIP_ASSERT("r->p != NULL", (r->p != NULL));
+    pbuf_free(r->p);
+    memp_free(MEMP_ND6_QUEUE, r);
+  }
+}
+#endif /* LWIP_ND6_QUEUEING */
+
+/**
+ * Send queued packets for a neighbor
+ *
+ * @param i the neighbor to send packets to
+ */
+static void
+nd6_send_q(s8_t i)
+{
+  struct ip6_hdr *ip6hdr;
+#if LWIP_ND6_QUEUEING
+  struct nd6_q_entry *q;
+#endif /* LWIP_ND6_QUEUEING */
+
+  if ((i < 0) || (i >= LWIP_ND6_NUM_NEIGHBORS)) {
+    return;
+  }
+
+#if LWIP_ND6_QUEUEING
+  while (neighbor_cache[i].q != NULL) {
+    /* remember first in queue */
+    q = neighbor_cache[i].q;
+    /* pop first item off the queue */
+    neighbor_cache[i].q = q->next;
+    /* Get ipv6 header. */
+    ip6hdr = (struct ip6_hdr *)(q->p->payload);
+    /* Override ip6_current_dest_addr() so that we have an aligned copy. */
+    ip6_addr_set(ip6_current_dest_addr(), &(ip6hdr->dest));
+    /* send the queued IPv6 packet */
+    (neighbor_cache[i].netif)->output_ip6(neighbor_cache[i].netif, q->p, ip6_current_dest_addr());
+    /* free the queued IP packet */
+    pbuf_free(q->p);
+    /* now queue entry can be freed */
+    memp_free(MEMP_ND6_QUEUE, q);
+  }
+#else /* LWIP_ND6_QUEUEING */
+  if (neighbor_cache[i].q != NULL) {
+    /* Get ipv6 header. */
+    ip6hdr = (struct ip6_hdr *)(neighbor_cache[i].q->payload);
+    /* Override ip6_current_dest_addr() so that we have an aligned copy. */
+    ip6_addr_set(ip6_current_dest_addr(), &(ip6hdr->dest));
+    /* send the queued IPv6 packet */
+    (neighbor_cache[i].netif)->output_ip6(neighbor_cache[i].netif, neighbor_cache[i].q, ip6_current_dest_addr());
+    /* free the queued IP packet */
+    pbuf_free(neighbor_cache[i].q);
+    neighbor_cache[i].q = NULL;
+  }
+#endif /* LWIP_ND6_QUEUEING */
+}
+
+
+/**
+ * Get the Path MTU for a destination.
+ *
+ * @param ip6addr the destination address
+ * @param netif the netif on which the packet will be sent
+ * @return the Path MTU, if known, or the netif default MTU
+ */
+u16_t
+nd6_get_destination_mtu(ip6_addr_t * ip6addr, struct netif * netif)
+{
+  s8_t i;
+
+  i = nd6_find_destination_cache_entry(ip6addr);
+  if (i >= 0) {
+    if (destination_cache[i].pmtu > 0) {
+      return destination_cache[i].pmtu;
+    }
+  }
+
+  if (netif != NULL) {
+    return netif->mtu;
+  }
+
+  return 1280; /* Minimum MTU */
+}
+
+
+#if LWIP_ND6_TCP_REACHABILITY_HINTS
+/**
+ * Provide the Neighbor discovery process with a hint that a
+ * destination is reachable. Called by tcp_receive when ACKs are
+ * received or sent (as per RFC). This is useful to avoid sending
+ * NS messages every 30 seconds.
+ *
+ * @param ip6addr the destination address which is know to be reachable
+ *                by an upper layer protocol (TCP)
+ */
+void
+nd6_reachability_hint(ip6_addr_t * ip6addr)
+{
+  s8_t i;
+
+  /* Find destination in cache. */
+  if (ip6_addr_cmp(ip6addr, &(destination_cache[nd6_cached_destination_index].destination_addr))) {
+    i = nd6_cached_destination_index;
+    ND6_STATS_INC(nd6.cachehit);
+  }
+  else {
+    i = nd6_find_destination_cache_entry(ip6addr);
+  }
+  if (i < 0) {
+    return;
+  }
+
+  /* Find next hop neighbor in cache. */
+  if (ip6_addr_cmp(&(destination_cache[i].next_hop_addr), &(neighbor_cache[nd6_cached_neighbor_index].next_hop_address))) {
+    i = nd6_cached_neighbor_index;
+    ND6_STATS_INC(nd6.cachehit);
+  }
+  else {
+    i = nd6_find_neighbor_cache_entry(&(destination_cache[i].next_hop_addr));
+  }
+  if (i < 0) {
+    return;
+  }
+
+  /* Set reachability state. */
+  neighbor_cache[i].state = ND6_REACHABLE;
+  neighbor_cache[i].counter.reachable_time = reachable_time;
+}
+#endif /* LWIP_ND6_TCP_REACHABILITY_HINTS */
+
+#endif /* LWIP_IPV6 */
