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 /**
  * @file
  * Address Resolution Protocol module for IP over Ethernet
  *
  * Functionally, ARP is divided into two parts. The first maps an IP address
  * to a physical address when sending a packet, and the second part answers
  * requests from other machines for our physical address.
  *
  * This implementation complies with RFC 826 (Ethernet ARP). It supports
  * Gratuitious ARP from RFC3220 (IP Mobility Support for IPv4) section 4.6
  * if an interface calls etharp_gratuitous(our_netif) upon address change.
  */
 
 /*
  * Copyright (c) 2001-2003 Swedish Institute of Computer Science.
  * Copyright (c) 2003-2004 Leon Woestenberg <leon.woestenberg@axon.tv>
  * Copyright (c) 2003-2004 Axon Digital Design B.V., The Netherlands.
  * 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.
  *
  */
  
 #include "lwip/opt.h"
 
 #if LWIP_ARP /* don't build if not configured for use in lwipopts.h */
 
 #include "lwip/inet.h"
 #include "lwip/ip.h"
 #include "lwip/stats.h"
 #include "lwip/snmp.h"
 #include "lwip/dhcp.h"
 #include "lwip/autoip.h"
 #include "netif/etharp.h"
 
 #if PPPOE_SUPPORT
 #include "netif/ppp_oe.h"
 #endif /* PPPOE_SUPPORT */
 
 #include <string.h>
 
 /** the time an ARP entry stays valid after its last update,
  *  for ARP_TMR_INTERVAL = 5000, this is
  *  (240 * 5) seconds = 20 minutes.
  */
 #define ARP_MAXAGE 240
 /** the time an ARP entry stays pending after first request,
  *  for ARP_TMR_INTERVAL = 5000, this is
  *  (2 * 5) seconds = 10 seconds.
  * 
  *  @internal Keep this number at least 2, otherwise it might
  *  run out instantly if the timeout occurs directly after a request.
  */
 #define ARP_MAXPENDING 2
 
 #define HWTYPE_ETHERNET 1
 
 #define ARPH_HWLEN(hdr) (ntohs((hdr)->_hwlen_protolen) >> 8)
 #define ARPH_PROTOLEN(hdr) (ntohs((hdr)->_hwlen_protolen) & 0xff)
 
 #define ARPH_HWLEN_SET(hdr, len) (hdr)->_hwlen_protolen = htons(ARPH_PROTOLEN(hdr) | ((len) << 8))
 #define ARPH_PROTOLEN_SET(hdr, len) (hdr)->_hwlen_protolen = htons((len) | (ARPH_HWLEN(hdr) << 8))
 
 enum etharp_state {
   ETHARP_STATE_EMPTY = 0,
   ETHARP_STATE_PENDING,
   ETHARP_STATE_STABLE
 };
 
 struct etharp_entry {
 #if ARP_QUEUEING
   /** 
    * Pointer to queue of pending outgoing packets on this ARP entry.
    */
   struct etharp_q_entry *q;
 #endif
   struct ip_addr ipaddr;
   struct eth_addr ethaddr;
   enum etharp_state state;
   u8_t ctime;
   struct netif *netif;
 };
 
 const struct eth_addr ethbroadcast = {{0xff,0xff,0xff,0xff,0xff,0xff}};
 const struct eth_addr ethzero = {{0,0,0,0,0,0}};
 static struct etharp_entry arp_table[ARP_TABLE_SIZE];
 #if !LWIP_NETIF_HWADDRHINT
 static u8_t etharp_cached_entry;
 #endif
 
 /**
  * Try hard to create a new entry - we want the IP address to appear in
  * the cache (even if this means removing an active entry or so). */
 #define ETHARP_TRY_HARD 1
 #define ETHARP_FIND_ONLY  2
 
 #if LWIP_NETIF_HWADDRHINT
 #define NETIF_SET_HINT(netif, hint)  if (((netif) != NULL) && ((netif)->addr_hint != NULL))  \
                                       *((netif)->addr_hint) = (hint);
 static s8_t find_entry(struct ip_addr *ipaddr, u8_t flags, struct netif *netif);
 #else /* LWIP_NETIF_HWADDRHINT */
 static s8_t find_entry(struct ip_addr *ipaddr, u8_t flags);
 #endif /* LWIP_NETIF_HWADDRHINT */
 
 static err_t update_arp_entry(struct netif *netif, struct ip_addr *ipaddr, struct eth_addr *ethaddr, u8_t flags);
 
 
 /* Some checks, instead of etharp_init(): */
 #if (LWIP_ARP && (ARP_TABLE_SIZE > 0x7f))
   #error "If you want to use ARP, ARP_TABLE_SIZE must fit in an s8_t, so, you have to reduce it in your lwipopts.h"
 #endif
 
 
 #if ARP_QUEUEING
 /**
  * Free a complete queue of etharp entries
  *
  * @param q a qeueue of etharp_q_entry's to free
  */
 static void
 free_etharp_q(struct etharp_q_entry *q)
 {
   struct etharp_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_ARP_QUEUE, r);
   }
 }
 #endif
 
 /**
  * Clears expired entries in the ARP table.
  *
  * This function should be called every ETHARP_TMR_INTERVAL microseconds (5 seconds),
  * in order to expire entries in the ARP table.
  */
 void
 etharp_tmr(void)
 {
   u8_t i;
 
   LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer\n"));
   /* remove expired entries from the ARP table */
   for (i = 0; i < ARP_TABLE_SIZE; ++i) {
     arp_table[i].ctime++;
     if (((arp_table[i].state == ETHARP_STATE_STABLE) &&
          (arp_table[i].ctime >= ARP_MAXAGE)) ||
         ((arp_table[i].state == ETHARP_STATE_PENDING)  &&
          (arp_table[i].ctime >= ARP_MAXPENDING))) {
          /* pending or stable entry has become old! */
       LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer: expired %s entry %"U16_F".\n",
            arp_table[i].state == ETHARP_STATE_STABLE ? "stable" : "pending", (u16_t)i));
       /* clean up entries that have just been expired */
       /* remove from SNMP ARP index tree */
       snmp_delete_arpidx_tree(arp_table[i].netif, &arp_table[i].ipaddr);
 #if ARP_QUEUEING
       /* and empty packet queue */
       if (arp_table[i].q != NULL) {
         /* remove all queued packets */
         LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer: freeing entry %"U16_F", packet queue %p.\n", (u16_t)i, (void *)(arp_table[i].q)));
         free_etharp_q(arp_table[i].q);
         arp_table[i].q = NULL;
       }
 #endif
       /* recycle entry for re-use */      
       arp_table[i].state = ETHARP_STATE_EMPTY;
     }
 #if ARP_QUEUEING
     /* still pending entry? (not expired) */
     if (arp_table[i].state == ETHARP_STATE_PENDING) {
         /* resend an ARP query here? */
     }
 #endif
   }
 }
 
 /**
  * Search the ARP table for a matching or new entry.
  * 
  * If an IP address is given, return a pending or stable ARP entry that matches
  * the address. If no match is found, create a new entry with this address set,
  * but in state ETHARP_EMPTY. The caller must check and possibly change the
  * state of the returned entry.
  * 
  * If ipaddr is NULL, return a initialized new entry in state ETHARP_EMPTY.
  * 
  * In all cases, attempt to create new entries from an empty entry. If no
  * empty entries are available and ETHARP_TRY_HARD flag is set, recycle
  * old entries. Heuristic choose the least important entry for recycling.
  *
  * @param ipaddr IP address to find in ARP cache, or to add if not found.
  * @param flags
  * - ETHARP_TRY_HARD: Try hard to create a entry by allowing recycling of
  * active (stable or pending) entries.
  *  
  * @return The ARP entry index that matched or is created, ERR_MEM if no
  * entry is found or could be recycled.
  */
 static s8_t
 #if LWIP_NETIF_HWADDRHINT
 find_entry(struct ip_addr *ipaddr, u8_t flags, struct netif *netif)
 #else /* LWIP_NETIF_HWADDRHINT */
 find_entry(struct ip_addr *ipaddr, u8_t flags)
 #endif /* LWIP_NETIF_HWADDRHINT */
 {
   s8_t old_pending = ARP_TABLE_SIZE, old_stable = ARP_TABLE_SIZE;
   s8_t empty = ARP_TABLE_SIZE;
   u8_t i = 0, age_pending = 0, age_stable = 0;
 #if ARP_QUEUEING
   /* oldest entry with packets on queue */
   s8_t old_queue = ARP_TABLE_SIZE;
   /* its age */
   u8_t age_queue = 0;
 #endif
 
   /* First, test if the last call to this function asked for the
    * same address. If so, we're really fast! */
   if (ipaddr) {
     /* ipaddr to search for was given */
 #if LWIP_NETIF_HWADDRHINT
     if ((netif != NULL) && (netif->addr_hint != NULL)) {
       /* per-pcb cached entry was given */
       u8_t per_pcb_cache = *(netif->addr_hint);
       if ((per_pcb_cache < ARP_TABLE_SIZE) && arp_table[per_pcb_cache].state == ETHARP_STATE_STABLE) {
         /* the per-pcb-cached entry is stable */
         if (ip_addr_cmp(ipaddr, &arp_table[per_pcb_cache].ipaddr)) {
           /* per-pcb cached entry was the right one! */
           ETHARP_STATS_INC(etharp.cachehit);
           return per_pcb_cache;
         }
       }
     }
 #else /* #if LWIP_NETIF_HWADDRHINT */
     if (arp_table[etharp_cached_entry].state == ETHARP_STATE_STABLE) {
       /* the cached entry is stable */
       if (ip_addr_cmp(ipaddr, &arp_table[etharp_cached_entry].ipaddr)) {
         /* cached entry was the right one! */
         ETHARP_STATS_INC(etharp.cachehit);
         return etharp_cached_entry;
       }
     }
 #endif /* #if LWIP_NETIF_HWADDRHINT */
   }
 
   /**
    * a) do a search through the cache, remember candidates
    * b) select candidate entry
    * c) create new entry
    */
 
   /* a) in a single search sweep, do all of this
    * 1) remember the first empty entry (if any)
    * 2) remember the oldest stable entry (if any)
    * 3) remember the oldest pending entry without queued packets (if any)
    * 4) remember the oldest pending entry with queued packets (if any)
    * 5) search for a matching IP entry, either pending or stable
    *    until 5 matches, or all entries are searched for.
    */
 
   for (i = 0; i < ARP_TABLE_SIZE; ++i) {
     /* no empty entry found yet and now we do find one? */
     if ((empty == ARP_TABLE_SIZE) && (arp_table[i].state == ETHARP_STATE_EMPTY)) {
       LWIP_DEBUGF(ETHARP_DEBUG, ("find_entry: found empty entry %"U16_F"\n", (u16_t)i));
       /* remember first empty entry */
       empty = i;
     }
     /* pending entry? */
     else if (arp_table[i].state == ETHARP_STATE_PENDING) {
       /* if given, does IP address match IP address in ARP entry? */
       if (ipaddr && ip_addr_cmp(ipaddr, &arp_table[i].ipaddr)) {
         LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: found matching pending entry %"U16_F"\n", (u16_t)i));
         /* found exact IP address match, simply bail out */
 #if LWIP_NETIF_HWADDRHINT
         NETIF_SET_HINT(netif, i);
 #else /* #if LWIP_NETIF_HWADDRHINT */
         etharp_cached_entry = i;
 #endif /* #if LWIP_NETIF_HWADDRHINT */
         return i;
 #if ARP_QUEUEING
       /* pending with queued packets? */
       } else if (arp_table[i].q != NULL) {
         if (arp_table[i].ctime >= age_queue) {
           old_queue = i;
           age_queue = arp_table[i].ctime;
         }
 #endif
       /* pending without queued packets? */
       } else {
         if (arp_table[i].ctime >= age_pending) {
           old_pending = i;
           age_pending = arp_table[i].ctime;
         }
       }        
     }
     /* stable entry? */
     else if (arp_table[i].state == ETHARP_STATE_STABLE) {
       /* if given, does IP address match IP address in ARP entry? */
       if (ipaddr && ip_addr_cmp(ipaddr, &arp_table[i].ipaddr)) {
         LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: found matching stable entry %"U16_F"\n", (u16_t)i));
         /* found exact IP address match, simply bail out */
 #if LWIP_NETIF_HWADDRHINT
         NETIF_SET_HINT(netif, i);
 #else /* #if LWIP_NETIF_HWADDRHINT */
         etharp_cached_entry = i;
 #endif /* #if LWIP_NETIF_HWADDRHINT */
         return i;
       /* remember entry with oldest stable entry in oldest, its age in maxtime */
       } else if (arp_table[i].ctime >= age_stable) {
         old_stable = i;
         age_stable = arp_table[i].ctime;
       }
     }
   }
   /* { we have no match } => try to create a new entry */
    
   /* no empty entry found and not allowed to recycle? */
   if (((empty == ARP_TABLE_SIZE) && ((flags & ETHARP_TRY_HARD) == 0))
       /* or don't create new entry, only search? */
       || ((flags & ETHARP_FIND_ONLY) != 0)) {
     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: no empty entry found and not allowed to recycle\n"));
     return (s8_t)ERR_MEM;
   }
   
   /* b) choose the least destructive entry to recycle:
    * 1) empty entry
    * 2) oldest stable entry
    * 3) oldest pending entry without queued packets
    * 4) oldest pending entry with queued packets
    * 
    * { ETHARP_TRY_HARD is set at this point }
    */ 
 
   /* 1) empty entry available? */
   if (empty < ARP_TABLE_SIZE) {
     i = empty;
     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: selecting empty entry %"U16_F"\n", (u16_t)i));
   }
   /* 2) found recyclable stable entry? */
   else if (old_stable < ARP_TABLE_SIZE) {
     /* recycle oldest stable*/
     i = old_stable;
     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: selecting oldest stable entry %"U16_F"\n", (u16_t)i));
 #if ARP_QUEUEING
     /* no queued packets should exist on stable entries */
     LWIP_ASSERT("arp_table[i].q == NULL", arp_table[i].q == NULL);
 #endif
   /* 3) found recyclable pending entry without queued packets? */
   } else if (old_pending < ARP_TABLE_SIZE) {
     /* recycle oldest pending */
     i = old_pending;
     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: selecting oldest pending entry %"U16_F" (without queue)\n", (u16_t)i));
 #if ARP_QUEUEING
   /* 4) found recyclable pending entry with queued packets? */
   } else if (old_queue < ARP_TABLE_SIZE) {
     /* recycle oldest pending */
     i = old_queue;
     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: selecting oldest pending entry %"U16_F", freeing packet queue %p\n", (u16_t)i, (void *)(arp_table[i].q)));
     free_etharp_q(arp_table[i].q);
     arp_table[i].q = NULL;
 #endif
     /* no empty or recyclable entries found */
   } else {
     return (s8_t)ERR_MEM;
   }
 
   /* { empty or recyclable entry found } */
   LWIP_ASSERT("i < ARP_TABLE_SIZE", i < ARP_TABLE_SIZE);
 
   if (arp_table[i].state != ETHARP_STATE_EMPTY)
   {
     snmp_delete_arpidx_tree(arp_table[i].netif, &arp_table[i].ipaddr);
   }
   /* recycle entry (no-op for an already empty entry) */
   arp_table[i].state = ETHARP_STATE_EMPTY;
 
   /* IP address given? */
   if (ipaddr != NULL) {
     /* set IP address */
     ip_addr_set(&arp_table[i].ipaddr, ipaddr);
   }
   arp_table[i].ctime = 0;
 #if LWIP_NETIF_HWADDRHINT
   NETIF_SET_HINT(netif, i);
 #else /* #if LWIP_NETIF_HWADDRHINT */
   etharp_cached_entry = i;
 #endif /* #if LWIP_NETIF_HWADDRHINT */
   return (err_t)i;
 }
 
 /**
  * Send an IP packet on the network using netif->linkoutput
  * The ethernet header is filled in before sending.
  *
  * @params netif the lwIP network interface on which to send the packet
  * @params p the packet to send, p->payload pointing to the (uninitialized) ethernet header
  * @params src the source MAC address to be copied into the ethernet header
  * @params dst the destination MAC address to be copied into the ethernet header
  * @return ERR_OK if the packet was sent, any other err_t on failure
  */
 static err_t
 etharp_send_ip(struct netif *netif, struct pbuf *p, struct eth_addr *src, struct eth_addr *dst)
 {
   struct eth_hdr *ethhdr = p->payload;
   u8_t k;
 
   LWIP_ASSERT("netif->hwaddr_len must be the same as ETHARP_HWADDR_LEN for etharp!",
               (netif->hwaddr_len == ETHARP_HWADDR_LEN));
   k = ETHARP_HWADDR_LEN;
   while(k > 0) {
     k--;
     ethhdr->dest.addr[k] = dst->addr[k];
     ethhdr->src.addr[k]  = src->addr[k];
   }
   ethhdr->type = htons(ETHTYPE_IP);
   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_send_ip: sending packet %p\n", (void *)p));
   /* send the packet */
   return netif->linkoutput(netif, p);
 }
 
 /**
  * Update (or insert) a IP/MAC address pair in the ARP cache.
  *
  * If a pending entry is resolved, any queued packets will be sent
  * at this point.
  * 
  * @param ipaddr IP address of the inserted ARP entry.
  * @param ethaddr Ethernet address of the inserted ARP entry.
  * @param flags Defines behaviour:
  * - ETHARP_TRY_HARD Allows ARP to insert this as a new item. If not specified,
  * only existing ARP entries will be updated.
  *
  * @return
  * - ERR_OK Succesfully updated ARP cache.
  * - ERR_MEM If we could not add a new ARP entry when ETHARP_TRY_HARD was set.
  * - ERR_ARG Non-unicast address given, those will not appear in ARP cache.
  *
  * @see pbuf_free()
  */
 static err_t
 update_arp_entry(struct netif *netif, struct ip_addr *ipaddr, struct eth_addr *ethaddr, u8_t flags)
 {
   s8_t i;
   u8_t k;
   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("update_arp_entry()\n"));
   LWIP_ASSERT("netif->hwaddr_len == ETHARP_HWADDR_LEN", netif->hwaddr_len == ETHARP_HWADDR_LEN);
   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("update_arp_entry: %"U16_F".%"U16_F".%"U16_F".%"U16_F" - %02"X16_F":%02"X16_F":%02"X16_F":%02"X16_F":%02"X16_F":%02"X16_F"\n",
                                         ip4_addr1(ipaddr), ip4_addr2(ipaddr), ip4_addr3(ipaddr), ip4_addr4(ipaddr), 
                                         ethaddr->addr[0], ethaddr->addr[1], ethaddr->addr[2],
                                         ethaddr->addr[3], ethaddr->addr[4], ethaddr->addr[5]));
   /* non-unicast address? */
   if (ip_addr_isany(ipaddr) ||
       ip_addr_isbroadcast(ipaddr, netif) ||
       ip_addr_ismulticast(ipaddr)) {
     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("update_arp_entry: will not add non-unicast IP address to ARP cache\n"));
     return ERR_ARG;
   }
   /* find or create ARP entry */
 #if LWIP_NETIF_HWADDRHINT
   i = find_entry(ipaddr, flags, netif);
 #else /* LWIP_NETIF_HWADDRHINT */
   i = find_entry(ipaddr, flags);
 #endif /* LWIP_NETIF_HWADDRHINT */
   /* bail out if no entry could be found */
   if (i < 0)
     return (err_t)i;
   
   /* mark it stable */
   arp_table[i].state = ETHARP_STATE_STABLE;
   /* record network interface */
   arp_table[i].netif = netif;
 
   /* insert in SNMP ARP index tree */
   snmp_insert_arpidx_tree(netif, &arp_table[i].ipaddr);
 
   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("update_arp_entry: updating stable entry %"S16_F"\n", (s16_t)i));
   /* update address */
   k = ETHARP_HWADDR_LEN;
   while (k > 0) {
     k--;
     arp_table[i].ethaddr.addr[k] = ethaddr->addr[k];
   }
   /* reset time stamp */
   arp_table[i].ctime = 0;
 #if ARP_QUEUEING
   /* this is where we will send out queued packets! */
   while (arp_table[i].q != NULL) {
     struct pbuf *p;
     /* remember remainder of queue */
     struct etharp_q_entry *q = arp_table[i].q;
     /* pop first item off the queue */
     arp_table[i].q = q->next;
     /* get the packet pointer */
     p = q->p;
     /* now queue entry can be freed */
     memp_free(MEMP_ARP_QUEUE, q);
     /* send the queued IP packet */
     etharp_send_ip(netif, p, (struct eth_addr*)(netif->hwaddr), ethaddr);
     /* free the queued IP packet */
     pbuf_free(p);
   }
 #endif
   return ERR_OK;
 }
 
 /**
  * Finds (stable) ethernet/IP address pair from ARP table
  * using interface and IP address index.
  * @note the addresses in the ARP table are in network order!
  *
  * @param netif points to interface index
  * @param ipaddr points to the (network order) IP address index
  * @param eth_ret points to return pointer
  * @param ip_ret points to return pointer
  * @return table index if found, -1 otherwise
  */
 s8_t
 etharp_find_addr(struct netif *netif, struct ip_addr *ipaddr,
          struct eth_addr **eth_ret, struct ip_addr **ip_ret)
 {
   s8_t i;
 
   LWIP_UNUSED_ARG(netif);
 
 #if LWIP_NETIF_HWADDRHINT
   i = find_entry(ipaddr, ETHARP_FIND_ONLY, NULL);
 #else /* LWIP_NETIF_HWADDRHINT */
   i = find_entry(ipaddr, ETHARP_FIND_ONLY);
 #endif /* LWIP_NETIF_HWADDRHINT */
   if((i >= 0) && arp_table[i].state == ETHARP_STATE_STABLE) {
       *eth_ret = &arp_table[i].ethaddr;
       *ip_ret = &arp_table[i].ipaddr;
       return i;
   }
   return -1;
 }
 
 /**
  * Updates the ARP table using the given IP packet.
  *
  * Uses the incoming IP packet's source address to update the
  * ARP cache for the local network. The function does not alter
  * or free the packet. This function must be called before the
  * packet p is passed to the IP layer.
  *
  * @param netif The lwIP network interface on which the IP packet pbuf arrived.
  * @param p The IP packet that arrived on netif.
  *
  * @return NULL
  *
  * @see pbuf_free()
  */
 void
 etharp_ip_input(struct netif *netif, struct pbuf *p)
 {
   struct eth_hdr *ethhdr;
   struct ip_hdr *iphdr;
   LWIP_ERROR("netif != NULL", (netif != NULL), return;);
   /* Only insert an entry if the source IP address of the
      incoming IP packet comes from a host on the local network. */
   ethhdr = p->payload;
   iphdr = (struct ip_hdr *)((u8_t*)ethhdr + SIZEOF_ETH_HDR);
 #if ETHARP_SUPPORT_VLAN
   if (ethhdr->type == ETHTYPE_VLAN) {
     iphdr = (struct ip_hdr *)((u8_t*)ethhdr + SIZEOF_ETH_HDR + SIZEOF_VLAN_HDR);
   }
 #endif /* ETHARP_SUPPORT_VLAN */
 
   /* source is not on the local network? */
   if (!ip_addr_netcmp(&(iphdr->src), &(netif->ip_addr), &(netif->netmask))) {
     /* do nothing */
     return;
   }
 
   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_ip_input: updating ETHARP table.\n"));
   /* update ARP table */
   /* @todo We could use ETHARP_TRY_HARD if we think we are going to talk
    * back soon (for example, if the destination IP address is ours. */
   update_arp_entry(netif, &(iphdr->src), &(ethhdr->src), 0);
 }
 
 
 /**
  * Responds to ARP requests to us. Upon ARP replies to us, add entry to cache  
  * send out queued IP packets. Updates cache with snooped address pairs.
  *
  * Should be called for incoming ARP packets. The pbuf in the argument
  * is freed by this function.
  *
  * @param netif The lwIP network interface on which the ARP packet pbuf arrived.
  * @param ethaddr Ethernet address of netif.
  * @param p The ARP packet that arrived on netif. Is freed by this function.
  *
  * @return NULL
  *
  * @see pbuf_free()
  */
 void
 etharp_arp_input(struct netif *netif, struct eth_addr *ethaddr, struct pbuf *p)
 {
   struct etharp_hdr *hdr;
   struct eth_hdr *ethhdr;
   /* these are aligned properly, whereas the ARP header fields might not be */
   struct ip_addr sipaddr, dipaddr;
   u8_t i;
   u8_t for_us;
 #if LWIP_AUTOIP
   const u8_t * ethdst_hwaddr;
 #endif /* LWIP_AUTOIP */
 
   LWIP_ERROR("netif != NULL", (netif != NULL), return;);
   
   /* drop short ARP packets: we have to check for p->len instead of p->tot_len here
      since a struct etharp_hdr is pointed to p->payload, so it musn't be chained! */
   if (p->len < SIZEOF_ETHARP_PACKET) {
     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
       ("etharp_arp_input: packet dropped, too short (%"S16_F"/%"S16_F")\n", p->tot_len,
       (s16_t)SIZEOF_ETHARP_PACKET));
     ETHARP_STATS_INC(etharp.lenerr);
     ETHARP_STATS_INC(etharp.drop);
     pbuf_free(p);
     return;
   }
 
   ethhdr = p->payload;
   hdr = (struct etharp_hdr *)((u8_t*)ethhdr + SIZEOF_ETH_HDR);
 #if ETHARP_SUPPORT_VLAN
   if (ethhdr->type == ETHTYPE_VLAN) {
     hdr = (struct etharp_hdr *)(((u8_t*)ethhdr) + SIZEOF_ETH_HDR + SIZEOF_VLAN_HDR);
   }
 #endif /* ETHARP_SUPPORT_VLAN */
 
   /* RFC 826 "Packet Reception": */
   if ((hdr->hwtype != htons(HWTYPE_ETHERNET)) ||
       (hdr->_hwlen_protolen != htons((ETHARP_HWADDR_LEN << 8) | sizeof(struct ip_addr))) ||
       (hdr->proto != htons(ETHTYPE_IP)) ||
       (ethhdr->type != htons(ETHTYPE_ARP)))  {
     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
       ("etharp_arp_input: packet dropped, wrong hw type, hwlen, proto, protolen or ethernet type (%"U16_F"/%"U16_F"/%"U16_F"/%"U16_F"/%"U16_F")\n",
       hdr->hwtype, ARPH_HWLEN(hdr), hdr->proto, ARPH_PROTOLEN(hdr), ethhdr->type));
     ETHARP_STATS_INC(etharp.proterr);
     ETHARP_STATS_INC(etharp.drop);
     pbuf_free(p);
     return;
   }
   ETHARP_STATS_INC(etharp.recv);
 
 #if LWIP_AUTOIP
   /* We have to check if a host already has configured our random
    * created link local address and continously check if there is
    * a host with this IP-address so we can detect collisions */
   autoip_arp_reply(netif, hdr);
 #endif /* LWIP_AUTOIP */
 
   /* Copy struct ip_addr2 to aligned ip_addr, to support compilers without
    * structure packing (not using structure copy which breaks strict-aliasing rules). */
   SMEMCPY(&sipaddr, &hdr->sipaddr, sizeof(sipaddr));
   SMEMCPY(&dipaddr, &hdr->dipaddr, sizeof(dipaddr));
 
   /* this interface is not configured? */
   if (netif->ip_addr.addr == 0) {
     for_us = 0;
   } else {
     /* ARP packet directed to us? */
     for_us = ip_addr_cmp(&dipaddr, &(netif->ip_addr));
   }
 
   /* ARP message directed to us? */
   if (for_us) {
     /* add IP address in ARP cache; assume requester wants to talk to us.
      * can result in directly sending the queued packets for this host. */
     update_arp_entry(netif, &sipaddr, &(hdr->shwaddr), ETHARP_TRY_HARD);
   /* ARP message not directed to us? */
   } else {
     /* update the source IP address in the cache, if present */
     update_arp_entry(netif, &sipaddr, &(hdr->shwaddr), 0);
   }
 
   /* now act on the message itself */
   switch (htons(hdr->opcode)) {
   /* ARP request? */
   case ARP_REQUEST:
     /* ARP request. If it asked for our address, we send out a
      * reply. In any case, we time-stamp any existing ARP entry,
      * and possiby send out an IP packet that was queued on it. */
 
     LWIP_DEBUGF (ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: incoming ARP request\n"));
     /* ARP request for our address? */
     if (for_us) {
 
       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: replying to ARP request for our IP address\n"));
       /* Re-use pbuf to send ARP reply.
          Since we are re-using an existing pbuf, we can't call etharp_raw since
          that would allocate a new pbuf. */
       hdr->opcode = htons(ARP_REPLY);
 
       hdr->dipaddr = hdr->sipaddr;
       SMEMCPY(&hdr->sipaddr, &netif->ip_addr, sizeof(hdr->sipaddr));
 
       LWIP_ASSERT("netif->hwaddr_len must be the same as ETHARP_HWADDR_LEN for etharp!",
                   (netif->hwaddr_len == ETHARP_HWADDR_LEN));
       i = ETHARP_HWADDR_LEN;
 #if LWIP_AUTOIP
       /* If we are using Link-Local, ARP packets must be broadcast on the
        * link layer. (See RFC3927 Section 2.5) */
       ethdst_hwaddr = ((netif->autoip != NULL) && (netif->autoip->state != AUTOIP_STATE_OFF)) ? (u8_t*)(ethbroadcast.addr) : hdr->shwaddr.addr;
 #endif /* LWIP_AUTOIP */
 
       while(i > 0) {
         i--;
         hdr->dhwaddr.addr[i] = hdr->shwaddr.addr[i];
 #if LWIP_AUTOIP
         ethhdr->dest.addr[i] = ethdst_hwaddr[i];
 #else  /* LWIP_AUTOIP */
         ethhdr->dest.addr[i] = hdr->shwaddr.addr[i];
 #endif /* LWIP_AUTOIP */
         hdr->shwaddr.addr[i] = ethaddr->addr[i];
         ethhdr->src.addr[i] = ethaddr->addr[i];
       }
 
       /* hwtype, hwaddr_len, proto, protolen and the type in the ethernet header
          are already correct, we tested that before */
 
       /* return ARP reply */
       netif->linkoutput(netif, p);
     /* we are not configured? */
     } else if (netif->ip_addr.addr == 0) {
       /* { for_us == 0 and netif->ip_addr.addr == 0 } */
       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: we are unconfigured, ARP request ignored.\n"));
     /* request was not directed to us */
     } else {
       /* { for_us == 0 and netif->ip_addr.addr != 0 } */
       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: ARP request was not for us.\n"));
     }
     break;
   case ARP_REPLY:
     /* ARP reply. We already updated the ARP cache earlier. */
     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: incoming ARP reply\n"));
 #if (LWIP_DHCP && DHCP_DOES_ARP_CHECK)
     /* DHCP wants to know about ARP replies from any host with an
      * IP address also offered to us by the DHCP server. We do not
      * want to take a duplicate IP address on a single network.
      * @todo How should we handle redundant (fail-over) interfaces? */
     dhcp_arp_reply(netif, &sipaddr);
 #endif
     break;
   default:
     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: ARP unknown opcode type %"S16_F"\n", htons(hdr->opcode)));
     ETHARP_STATS_INC(etharp.err);
     break;
   }
   /* free ARP packet */
   pbuf_free(p);
 }
 
 /**
  * Resolve and fill-in Ethernet address header for outgoing IP packet.
  *
  * For IP multicast and broadcast, corresponding Ethernet addresses
  * are selected and the packet is transmitted on the link.
  *
  * For unicast addresses, the packet is submitted to etharp_query(). In
  * case the IP address is outside the local network, the IP address of
  * the gateway is used.
  *
  * @param netif The lwIP network interface which the IP packet will be sent on.
  * @param q The pbuf(s) containing the IP packet to be sent.
  * @param ipaddr The IP address of the packet destination.
  *
  * @return
  * - ERR_RTE No route to destination (no gateway to external networks),
  * or the return type of either etharp_query() or etharp_send_ip().
  */
 err_t
 etharp_output(struct netif *netif, struct pbuf *q, struct ip_addr *ipaddr)
 {
   struct eth_addr *dest, mcastaddr;
 
   /* make room for Ethernet header - should not fail */
   if (pbuf_header(q, sizeof(struct eth_hdr)) != 0) {
     /* bail out */
     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
       ("etharp_output: could not allocate room for header.\n"));
     LINK_STATS_INC(link.lenerr);
     return ERR_BUF;
   }
 
   /* assume unresolved Ethernet address */
   dest = NULL;
   /* Determine on destination hardware address. Broadcasts and multicasts
    * are special, other IP addresses are looked up in the ARP table. */
 
   /* broadcast destination IP address? */
   if (ip_addr_isbroadcast(ipaddr, netif)) {
     /* broadcast on Ethernet also */
     dest = (struct eth_addr *)&ethbroadcast;
   /* multicast destination IP address? */
   } else if (ip_addr_ismulticast(ipaddr)) {
     /* Hash IP multicast address to MAC address.*/
     mcastaddr.addr[0] = 0x01;
     mcastaddr.addr[1] = 0x00;
     mcastaddr.addr[2] = 0x5e;
     mcastaddr.addr[3] = ip4_addr2(ipaddr) & 0x7f;
     mcastaddr.addr[4] = ip4_addr3(ipaddr);
     mcastaddr.addr[5] = ip4_addr4(ipaddr);
     /* destination Ethernet address is multicast */
     dest = &mcastaddr;
   /* unicast destination IP address? */
   } else {
     /* outside local network? */
     if (!ip_addr_netcmp(ipaddr, &(netif->ip_addr), &(netif->netmask))) {
       /* interface has default gateway? */
       if (netif->gw.addr != 0) {
         /* send to hardware address of default gateway IP address */
         ipaddr = &(netif->gw);
       /* no default gateway available */
       } else {
         /* no route to destination error (default gateway missing) */
         return ERR_RTE;
       }
     }
     /* queue on destination Ethernet address belonging to ipaddr */
     return etharp_query(netif, ipaddr, q);
   }
 
   /* continuation for multicast/broadcast destinations */
   /* obtain source Ethernet address of the given interface */
   /* send packet directly on the link */
   return etharp_send_ip(netif, q, (struct eth_addr*)(netif->hwaddr), dest);
 }
 
 /**
  * Send an ARP request for the given IP address and/or queue a packet.
  *
  * If the IP address was not yet in the cache, a pending ARP cache entry
  * is added and an ARP request is sent for the given address. The packet
  * is queued on this entry.
  *
  * If the IP address was already pending in the cache, a new ARP request
  * is sent for the given address. The packet is queued on this entry.
  *
  * If the IP address was already stable in the cache, and a packet is
  * given, it is directly sent and no ARP request is sent out. 
  * 
  * If the IP address was already stable in the cache, and no packet is
  * given, an ARP request is sent out.
  * 
  * @param netif The lwIP network interface on which ipaddr
  * must be queried for.
  * @param ipaddr The IP address to be resolved.
  * @param q If non-NULL, a pbuf that must be delivered to the IP address.
  * q is not freed by this function.
  *
  * @note q must only be ONE packet, not a packet queue!
  *
  * @return
  * - ERR_BUF Could not make room for Ethernet header.
  * - ERR_MEM Hardware address unknown, and no more ARP entries available
  *   to query for address or queue the packet.
  * - ERR_MEM Could not queue packet due to memory shortage.
  * - ERR_RTE No route to destination (no gateway to external networks).
  * - ERR_ARG Non-unicast address given, those will not appear in ARP cache.
  *
  */
 err_t
 etharp_query(struct netif *netif, struct ip_addr *ipaddr, struct pbuf *q)
 {
   struct eth_addr * srcaddr = (struct eth_addr *)netif->hwaddr;
   err_t result = ERR_MEM;
   s8_t i; /* ARP entry index */
 
   /* non-unicast address? */
   if (ip_addr_isbroadcast(ipaddr, netif) ||
       ip_addr_ismulticast(ipaddr) ||
       ip_addr_isany(ipaddr)) {
     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: will not add non-unicast IP address to ARP cache\n"));
     return ERR_ARG;
   }
 
   /* find entry in ARP cache, ask to create entry if queueing packet */
 #if LWIP_NETIF_HWADDRHINT
   i = find_entry(ipaddr, ETHARP_TRY_HARD, netif);
 #else /* LWIP_NETIF_HWADDRHINT */
   i = find_entry(ipaddr, ETHARP_TRY_HARD);
 #endif /* LWIP_NETIF_HWADDRHINT */
 
   /* could not find or create entry? */
   if (i < 0) {
     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: could not create ARP entry\n"));
     if (q) {
       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: packet dropped\n"));
       ETHARP_STATS_INC(etharp.memerr);
     }
     return (err_t)i;
   }
 
   /* mark a fresh entry as pending (we just sent a request) */
   if (arp_table[i].state == ETHARP_STATE_EMPTY) {
     arp_table[i].state = ETHARP_STATE_PENDING;
   }
 
   /* { i is either a STABLE or (new or existing) PENDING entry } */
   LWIP_ASSERT("arp_table[i].state == PENDING or STABLE",
   ((arp_table[i].state == ETHARP_STATE_PENDING) ||
    (arp_table[i].state == ETHARP_STATE_STABLE)));
 
   /* do we have a pending entry? or an implicit query request? */
   if ((arp_table[i].state == ETHARP_STATE_PENDING) || (q == NULL)) {
     /* try to resolve it; send out ARP request */
     result = etharp_request(netif, ipaddr);
     if (result != ERR_OK) {
       /* ARP request couldn't be sent */
       /* We don't re-send arp request in etharp_tmr, but we still queue packets,
          since this failure could be temporary, and the next packet calling
          etharp_query again could lead to sending the queued packets. */
     }
   }
   
   /* packet given? */
   if (q != NULL) {
     /* stable entry? */
     if (arp_table[i].state == ETHARP_STATE_STABLE) {
       /* we have a valid IP->Ethernet address mapping */
       /* send the packet */
       result = etharp_send_ip(netif, q, srcaddr, &(arp_table[i].ethaddr));
     /* pending entry? (either just created or already pending */
     } else if (arp_table[i].state == ETHARP_STATE_PENDING) {
 #if ARP_QUEUEING /* queue the given q packet */
       struct pbuf *p;
       int copy_needed = 0;
       /* 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) {
         LWIP_ASSERT("no packet queues allowed!", (p->len != p->tot_len) || (p->next == 0));
         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_RAW, p->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 could be taken over? */
       if (p != NULL) {
         /* queue packet ... */
         struct etharp_q_entry *new_entry;
         /* allocate a new arp queue entry */
         new_entry = memp_malloc(MEMP_ARP_QUEUE);
         if (new_entry != NULL) {
           new_entry->next = 0;
           new_entry->p = p;
           if(arp_table[i].q != NULL) {
             /* queue was already existent, append the new entry to the end */
             struct etharp_q_entry *r;
             r = arp_table[i].q;
             while (r->next != NULL) {
               r = r->next;
             }
             r->next = new_entry;
           } else {
             /* queue did not exist, first item in queue */
             arp_table[i].q = new_entry;
           }
           LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: queued packet %p on ARP entry %"S16_F"\n", (void *)q, (s16_t)i));
           result = ERR_OK;
         } else {
           /* the pool MEMP_ARP_QUEUE is empty */
           pbuf_free(p);
           LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: could not queue a copy of PBUF_REF packet %p (out of memory)\n", (void *)q));
           /* { result == ERR_MEM } through initialization */
         }
       } else {
         ETHARP_STATS_INC(etharp.memerr);
         LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: could not queue a copy of PBUF_REF packet %p (out of memory)\n", (void *)q));
         /* { result == ERR_MEM } through initialization */
       }
 #else /* ARP_QUEUEING == 0 */
       /* q && state == PENDING && ARP_QUEUEING == 0 => result = ERR_MEM */
       /* { result == ERR_MEM } through initialization */
       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: Ethernet destination address unknown, queueing disabled, packet %p dropped\n", (void *)q));
 #endif
     }
   }
   return result;
 }
 
 /**
  * Send a raw ARP packet (opcode and all addresses can be modified)
  *
  * @param netif the lwip network interface on which to send the ARP packet
  * @param ethsrc_addr the source MAC address for the ethernet header
  * @param ethdst_addr the destination MAC address for the ethernet header
  * @param hwsrc_addr the source MAC address for the ARP protocol header
  * @param ipsrc_addr the source IP address for the ARP protocol header
  * @param hwdst_addr the destination MAC address for the ARP protocol header
  * @param ipdst_addr the destination IP address for the ARP protocol header
  * @param opcode the type of the ARP packet
  * @return ERR_OK if the ARP packet has been sent
  *         ERR_MEM if the ARP packet couldn't be allocated
  *         any other err_t on failure
  */
 #if !LWIP_AUTOIP
 static
 #endif /* LWIP_AUTOIP */
 err_t
 etharp_raw(struct netif *netif, const struct eth_addr *ethsrc_addr,
            const struct eth_addr *ethdst_addr,
            const struct eth_addr *hwsrc_addr, const struct ip_addr *ipsrc_addr,
            const struct eth_addr *hwdst_addr, const struct ip_addr *ipdst_addr,
            const u16_t opcode)
 {
   struct pbuf *p;
   err_t result = ERR_OK;
   u8_t k; /* ARP entry index */
   struct eth_hdr *ethhdr;
   struct etharp_hdr *hdr;
 #if LWIP_AUTOIP
   const u8_t * ethdst_hwaddr;
 #endif /* LWIP_AUTOIP */
 
   /* allocate a pbuf for the outgoing ARP request packet */
   p = pbuf_alloc(PBUF_RAW, SIZEOF_ETHARP_PACKET, PBUF_RAM);
   /* could allocate a pbuf for an ARP request? */
   if (p == NULL) {
     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
       ("etharp_raw: could not allocate pbuf for ARP request.\n"));
     ETHARP_STATS_INC(etharp.memerr);
     return ERR_MEM;
   }
   LWIP_ASSERT("check that first pbuf can hold struct etharp_hdr",
               (p->len >= SIZEOF_ETHARP_PACKET));
 
   ethhdr = p->payload;
   hdr = (struct etharp_hdr *)((u8_t*)ethhdr + SIZEOF_ETH_HDR);
   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_raw: sending raw ARP packet.\n"));
   hdr->opcode = htons(opcode);
 
   LWIP_ASSERT("netif->hwaddr_len must be the same as ETHARP_HWADDR_LEN for etharp!",
               (netif->hwaddr_len == ETHARP_HWADDR_LEN));
   k = ETHARP_HWADDR_LEN;
 #if LWIP_AUTOIP
   /* If we are using Link-Local, ARP packets must be broadcast on the
    * link layer. (See RFC3927 Section 2.5) */
   ethdst_hwaddr = ((netif->autoip != NULL) && (netif->autoip->state != AUTOIP_STATE_OFF)) ? (u8_t*)(ethbroadcast.addr) : ethdst_addr->addr;
 #endif /* LWIP_AUTOIP */
   /* Write MAC-Addresses (combined loop for both headers) */
   while(k > 0) {
     k--;
     /* Write the ARP MAC-Addresses */
     hdr->shwaddr.addr[k] = hwsrc_addr->addr[k];
     hdr->dhwaddr.addr[k] = hwdst_addr->addr[k];
     /* Write the Ethernet MAC-Addresses */
 #if LWIP_AUTOIP
     ethhdr->dest.addr[k] = ethdst_hwaddr[k];
 #else  /* LWIP_AUTOIP */
     ethhdr->dest.addr[k] = ethdst_addr->addr[k];
 #endif /* LWIP_AUTOIP */
     ethhdr->src.addr[k]  = ethsrc_addr->addr[k];
   }
   hdr->sipaddr = *(struct ip_addr2 *)ipsrc_addr;
   hdr->dipaddr = *(struct ip_addr2 *)ipdst_addr;
 
   hdr->hwtype = htons(HWTYPE_ETHERNET);
   hdr->proto = htons(ETHTYPE_IP);
   /* set hwlen and protolen together */
   hdr->_hwlen_protolen = htons((ETHARP_HWADDR_LEN << 8) | sizeof(struct ip_addr));
 
   ethhdr->type = htons(ETHTYPE_ARP);
   /* send ARP query */
   result = netif->linkoutput(netif, p);
   ETHARP_STATS_INC(etharp.xmit);
   /* free ARP query packet */
   pbuf_free(p);
   p = NULL;
   /* could not allocate pbuf for ARP request */
 
   return result;
 }
 
 /**
  * Send an ARP request packet asking for ipaddr.
  *
  * @param netif the lwip network interface on which to send the request
  * @param ipaddr the IP address for which to ask
  * @return ERR_OK if the request has been sent
  *         ERR_MEM if the ARP packet couldn't be allocated
  *         any other err_t on failure
  */
 err_t
 etharp_request(struct netif *netif, struct ip_addr *ipaddr)
 {
   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_request: sending ARP request.\n"));
   return etharp_raw(netif, (struct eth_addr *)netif->hwaddr, &ethbroadcast,
                     (struct eth_addr *)netif->hwaddr, &netif->ip_addr, &ethzero,
                     ipaddr, ARP_REQUEST);
 }
 
 /**
  * Process received ethernet frames. Using this function instead of directly
  * calling ip_input and passing ARP frames through etharp in ethernetif_input,
  * the ARP cache is protected from concurrent access.
  *
  * @param p the recevied packet, p->payload pointing to the ethernet header
  * @param netif the network interface on which the packet was received
  */
 err_t
 ethernet_input(struct pbuf *p, struct netif *netif)
 {
   struct eth_hdr* ethhdr;
   u16_t type;
 
   /* points to packet payload, which starts with an Ethernet header */
   ethhdr = p->payload;
   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE,
     ("ethernet_input: dest:%02x:%02x:%02x:%02x:%02x:%02x, src:%02x:%02x:%02x:%02x:%02x:%02x, type:%2hx\n",
      (unsigned)ethhdr->dest.addr[0], (unsigned)ethhdr->dest.addr[1], (unsigned)ethhdr->dest.addr[2],
      (unsigned)ethhdr->dest.addr[3], (unsigned)ethhdr->dest.addr[4], (unsigned)ethhdr->dest.addr[5],
      (unsigned)ethhdr->src.addr[0], (unsigned)ethhdr->src.addr[1], (unsigned)ethhdr->src.addr[2],
      (unsigned)ethhdr->src.addr[3], (unsigned)ethhdr->src.addr[4], (unsigned)ethhdr->src.addr[5],
      (unsigned)htons(ethhdr->type)));
 
   type = htons(ethhdr->type);
 #if ETHARP_SUPPORT_VLAN
   if (type == ETHTYPE_VLAN) {
     struct eth_vlan_hdr *vlan = (struct eth_vlan_hdr*)(((char*)ethhdr) + SIZEOF_ETH_HDR);
 #ifdef ETHARP_VLAN_CHECK /* if not, allow all VLANs */
     if (VLAN_ID(vlan) != ETHARP_VLAN_CHECK) {
       /* silently ignore this packet: not for our VLAN */
       pbuf_free(p);
       return ERR_OK;
     }
 #endif /* ETHARP_VLAN_CHECK */
     type = htons(vlan->tpid);
   }
 #endif /* ETHARP_SUPPORT_VLAN */
 
   switch (type) {
     /* IP packet? */
     case ETHTYPE_IP:
 #if ETHARP_TRUST_IP_MAC
       /* update ARP table */
       etharp_ip_input(netif, p);
 #endif /* ETHARP_TRUST_IP_MAC */
       /* skip Ethernet header */
       if(pbuf_header(p, -(s16_t)SIZEOF_ETH_HDR)) {
         LWIP_ASSERT("Can't move over header in packet", 0);
         pbuf_free(p);
         p = NULL;
       } else {
         /* pass to IP layer */
         ip_input(p, netif);
       }
       break;
       
     case ETHTYPE_ARP:
       /* pass p to ARP module */
       etharp_arp_input(netif, (struct eth_addr*)(netif->hwaddr), p);
       break;
 
 #if PPPOE_SUPPORT
     case ETHTYPE_PPPOEDISC: /* PPP Over Ethernet Discovery Stage */
       pppoe_disc_input(netif, p);
       break;
 
     case ETHTYPE_PPPOE: /* PPP Over Ethernet Session Stage */
       pppoe_data_input(netif, p);
       break;
 #endif /* PPPOE_SUPPORT */
 
     default:
       ETHARP_STATS_INC(etharp.proterr);
       ETHARP_STATS_INC(etharp.drop);
       pbuf_free(p);
       p = NULL;
       break;
   }
 
   /* This means the pbuf is freed or consumed,
      so the caller doesn't have to free it again */
   return ERR_OK;
 }
 #endif /* LWIP_ARP */