text: /****************************************************************************
   * net/neighbor/neighbor_out.c
   *
   *   Copyright (C) 2015 Gregory Nutt. All rights reserved.
   *   Author: Gregory Nutt <gnutt@nuttx.org>
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   * 3. Neither the name NuttX nor the names of its contributors may be
   *    used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
   * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
   * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   * POSSIBILITY OF SUCH DAMAGE.
   *
   ****************************************************************************/
  
  /****************************************************************************
   * Included Files
   ****************************************************************************/
  
  #include <nuttx/config.h>
  
  #include <string.h>
  #include <debug.h>
  
  #include <nuttx/net/arp.h>
  #include <nuttx/net/netdev.h>
  
  #include "route/route.h"
  #include "icmpv6/icmpv6.h"
  #include "neighbor/neighbor.h"
  
  /****************************************************************************
   * Pre-processor Definitions
   ****************************************************************************/
  
  #define ETHBUF  ((struct eth_hdr_s *)dev->d_buf)
  #define IPv6BUF ((struct ipv6_hdr_s *)&dev->d_buf[NET_LL_HDRLEN(dev)])
  
  /****************************************************************************
   * Private Types
   ****************************************************************************/
  
  /****************************************************************************
   * Private Data
   ****************************************************************************/
  
  /* Support for broadcast address */
  
  static const struct ether_addr g_broadcast_ethaddr =
  {
    {
      0xff, 0xff, 0xff, 0xff, 0xff, 0xff
    }
  };
  
  /* Support for IGMP multicast addresses.
   *
   * Well-known ethernet multicast address:
   *
   * ADDRESS           TYPE   USAGE
   * 01-00-0c-cc-cc-cc 0x0802 CDP (Cisco Discovery Protocol), VTP (Virtual Trunking Protocol)
   * 01-00-0c-cc-cc-cd 0x0802 Cisco Shared Spanning Tree Protocol Address
   * 01-80-c2-00-00-00 0x0802 Spanning Tree Protocol (for bridges) IEEE 802.1D
   * 01-80-c2-00-00-02 0x0809 Ethernet OAM Protocol IEEE 802.3ah
   * 01-00-5e-xx-xx-xx 0x0800 IPv4 IGMP Multicast Address
   * 33-33-00-00-00-00 0x86DD IPv6 Neighbor Discovery
   * 33-33-xx-xx-xx-xx 0x86DD IPv6 Multicast Address (RFC3307)
   *
   * The following is the first three octects of the IGMP address:
   */
  
  #ifdef CONFIG_NET_IGMP
  static const uint8_t g_multicast_ethaddr[3] =
  {
    0x01, 0x00, 0x5e
  };
  #endif
  
  /****************************************************************************
   * Private Functions
   ****************************************************************************/
  
  /****************************************************************************
   * Public Functions
   ****************************************************************************/
  
  /****************************************************************************
   * Name: neighbor_out
   *
   * Description:
   *   This function should be called before sending out an IPv6 packet. The
   *   function checks the destination IPv6 address of the IPv6 packet to see
   *   what Ethernet MAC address that should be used as a destination MAC
   *   address on the Ethernet.
   *
   *   If the destination IPv6 address is in the local network (determined
   *   by logical ANDing of netmask and our IPv6 address), the function
   *   checks the Neighbor Table to see if an entry for the destination IPv6
   *   address is found.  If so, an Ethernet header is pre-pended at the
   *   beginning of the packet and the function returns.
   *
   *   If no Neighbor Table entry is found for the destination IPv6 address,
   *   the packet in the d_buf[] is replaced by an ICMPv6 Neighbor Solicit
   *   request packet for the IPv6 address. The IPv6 packet is dropped and 
   *   it is assumed that the higher level protocols (e.g., TCP) eventually
   *   will retransmit the dropped packet.
   *
   *   Upon return in either the case, a packet to be sent is present in the
   *   d_buf[] buffer and the d_len field holds the length of the Ethernet
   *   frame that should be transmitted.
   *
   ****************************************************************************/
  
  void neighbor_out(FAR struct net_driver_s *dev)
  {
    FAR const struct neighbor_addr_s *naddr;
    FAR struct eth_hdr_s *eth = ETHBUF;
    FAR struct ipv6_hdr_s *ip = IPv6BUF;
    net_ipv6addr_t ipaddr;
  
    /* Skip sending Neighbor Solicitations when the frame to be transmitted was
     * written into a packet socket or if we are sending certain Neighbor
     * messages (solicitation, advertisement, echo request).
     */
  
    if (IFF_IS_NOARP(dev->d_flags))
      {
        /* Clear the indication and let the packet continue on its way. */
  
        IFF_CLR_NOARP(dev->d_flags);
        return;
      }
  
    /* Find the destination IPv6 address in the Neighbor Table and construct
     * the Ethernet header. If the destination IPv6 address isn't on the local
     * network, we use the default router's IPv6 address instead.
     *
     * If no Neighbor Table entry is found, we overwrite the original IPv6
     * packet with an Neighbor Solicitation Request for the IPv6 address.
     */
  
    /* First check if destination is a IPv6 multicast address.  IPv6
     * multicast addresses in IPv6 have the prefix ff00::/8
     * 
     *   Bits 120-127: Prefix
     *   Bits 116-119: Flags (1, 2, or 3 defined)
     *   Bits 112-115: Scope
     *
     * REVISIT: Need to revisit IPv6 broadcast support.  Broadcast
     * IP addresses are not used with IPv6; multicast is used instead.
     * Does this mean that all multicast address should go to the
     * broadcast Ethernet address?
     */
  
    if ((ip->destipaddr[0] & HTONS(0xff00)) == HTONS(0xff00))
      {
        memcpy(eth->dest, g_broadcast_ethaddr.ether_addr_octet,
               ETHER_ADDR_LEN);
      }
  
  #ifdef CONFIG_NET_IGMP
    /* Check if the destination address is a multicast address
     *
     *   IPv6 multicast addresses are have the high-order octet of the
     *   addresses=0xff (ff00::/8.)
     *
     * REVISIT:  See comments above.  How do we distinguish broadcast
     * from IGMP multicast?
     */
  #warning Missing logic
  #endif
  
    else
      {
        /* Check if the destination address is on the local network. */
  
        if (!net_ipv6addr_maskcmp(ip->destipaddr, dev->d_ipv6addr,
                                  dev->d_ipv6netmask))
          {
            /* Destination address is not on the local network */
  
  #ifdef CONFIG_NET_ROUTE
            /* We have a routing table.. find the correct router to use in
             * this case (or, as a fall-back, use the device's default router
             * address).  We will use the router IPv6 address instead of the
             * destination address when determining the MAC address.
             */
  
            netdev_ipv6_router(dev, ip->destipaddr, ipaddr);
  #else
            /* Use the device's default router IPv6 address instead of the
             * destination address when determining the MAC address.
             */
  
            net_ipv6addr_copy(ipaddr, dev->d_ipv6draddr);
  #endif
          }
        else
          {
            /* Else, we use the destination IPv6 address. */
  
            net_ipv6addr_copy(ipaddr, ip->destipaddr);
          }
  
        /* Check if we already have this destination address in the Neighbor Table */
  
        naddr = neighbor_lookup(ipaddr);
        if (!naddr)
          {
             nllvdbg("IPv6 Neighbor solicitation for IPv6\n");
  
            /* The destination address was not in our Neighbor Table, so we
             * overwrite the IPv6 packet with an ICMDv6 Neighbor Solicitation
             * message.
             */
  
            icmpv6_solicit(dev, ipaddr);
            return;
          }
  
        /* Build an Ethernet header. */
  
        memcpy(eth->dest, naddr->na_addr.ether_addr_octet, ETHER_ADDR_LEN);
      }
  
    /* Finish populating the Ethernet header */
  
    memcpy(eth->src, dev->d_mac.ether_addr_octet, ETHER_ADDR_LEN);
    eth->type  = HTONS(ETHTYPE_IP6);
  
    /* Add the size of the layer layer header to the total size of the
     * outgoing packet.
     */
  
    dev->d_len += netdev_ipv6_hdrlen(dev);
    nllvdbg("Outgoing IPv6 Packet length: %d (%d)\n",
            dev->d_len, (ip->len[0] << 8) | ip->len[1]);
  }
  