Diff: lwip/netif/etharp.c

Revision:

0:632c9925f013

Child:

5:dd63a1e02b1b

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lwip/netif/etharp.c	Fri Jun 11 16:05:15 2010 +0000
@@ -0,0 +1,1241 @@
+/**
+ * @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 || LWIP_ETHERNET
+
+#include "lwip/ip_addr.h"
+#include "lwip/def.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>
+
+const struct eth_addr ethbroadcast = {{0xff,0xff,0xff,0xff,0xff,0xff}};
+const struct eth_addr ethzero = {{0,0,0,0,0,0}};
+
+#if LWIP_ARP /* don't build if not configured for use in lwipopts.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 /* ARP_QUEUEING */
+  ip_addr_t ipaddr;
+  struct eth_addr ethaddr;
+  enum etharp_state state;
+  u8_t ctime;
+  struct netif *netif;
+};
+
+static struct etharp_entry arp_table[ARP_TABLE_SIZE];
+#if !LWIP_NETIF_HWADDRHINT
+static u8_t etharp_cached_entry;
+#endif /* !LWIP_NETIF_HWADDRHINT */
+
+/**
+ * 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(ip_addr_t *ipaddr, u8_t flags, struct netif *netif);
+#else /* LWIP_NETIF_HWADDRHINT */
+static s8_t find_entry(ip_addr_t *ipaddr, u8_t flags);
+#endif /* LWIP_NETIF_HWADDRHINT */
+
+static err_t update_arp_entry(struct netif *netif, ip_addr_t *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 /* ARP_QUEUEING */
+
+/**
+ * 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 /* ARP_QUEUEING */
+      /* 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 /* ARP_QUEUEING */
+  }
+}
+
+/**
+ * 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(ip_addr_t *ipaddr, u8_t flags, struct netif *netif)
+#else /* LWIP_NETIF_HWADDRHINT */
+find_entry(ip_addr_t *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 /* ARP_QUEUEING */
+
+  /* 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 /* ARP_QUEUEING */
+      /* 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 */
+   
+  /* don't create new entry, only search? */
+  if (((flags & ETHARP_FIND_ONLY) != 0) ||
+      /* or no empty entry found and not allowed to recycle? */
+      ((empty == ARP_TABLE_SIZE) && ((flags & ETHARP_TRY_HARD) == 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 /* ARP_QUEUEING */
+  /* 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 /* ARP_QUEUEING */
+    /* 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_copy(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 = (struct eth_hdr *)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, ip_addr_t *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_16(ipaddr), ip4_addr2_16(ipaddr), ip4_addr3_16(ipaddr), ip4_addr4_16(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 /* ARP_QUEUEING */
+  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, ip_addr_t *ipaddr,
+         struct eth_addr **eth_ret, ip_addr_t **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;
+}
+#if ETHARP_TRUST_IP_MAC
+/**
+ * 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()
+ */
+static 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 = (struct eth_hdr *)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 the source IP address in the cache, if present */
+  /* @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), ETHARP_FIND_ONLY);
+}
+#endif /* ETHARP_TRUST_IP_MAC */
+
+/**
+ * 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()
+ */
+static 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 */
+  ip_addr_t 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 = (struct eth_hdr *)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(ip_addr_t))) ||
+      (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 (ip_addr_isany(&netif->ip_addr)) {
+    for_us = 0;
+  } else {
+    /* ARP packet directed to us? */
+    for_us = (u8_t)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), ETHARP_FIND_ONLY);
+  }
+
+  /* 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);
+
+      SMEMCPY(&hdr->dipaddr, &hdr->sipaddr, sizeof(ip_addr_t));
+      SMEMCPY(&hdr->sipaddr, &netif->ip_addr, sizeof(ip_addr_t));
+
+      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, all ARP packets that contain a Link-Local
+       * 'sender IP address' MUST be sent using link-layer broadcast instead of
+       * link-layer unicast. (See RFC3927 Section 2.5, last paragraph) */
+      ethdst_hwaddr = ip_addr_islinklocal(&netif->ip_addr) ? (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 (ip_addr_isany(&netif->ip_addr)) {
+      /* { 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 /* (LWIP_DHCP && DHCP_DOES_ARP_CHECK) */
+    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, ip_addr_t *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)) &&
+        !ip_addr_islinklocal(ipaddr)) {
+      /* interface has default gateway? */
+      if (!ip_addr_isany(&netif->gw)) {
+        /* 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, ip_addr_t *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 = (struct etharp_q_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 */
+      /* 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 /* ARP_QUEUEING */
+    }
+  }
+  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 ip_addr_t *ipsrc_addr,
+           const struct eth_addr *hwdst_addr, const ip_addr_t *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 = (struct eth_hdr *)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, all ARP packets that contain a Link-Local
+   * 'sender IP address' MUST be sent using link-layer broadcast instead of
+   * link-layer unicast. (See RFC3927 Section 2.5, last paragraph) */
+  ethdst_hwaddr = ip_addr_islinklocal(ipsrc_addr) ? (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];
+  }
+  /* Copy struct ip_addr2 to aligned ip_addr, to support compilers without
+   * structure packing. */ 
+  SMEMCPY(&hdr->sipaddr, ipsrc_addr, sizeof(ip_addr_t));
+  SMEMCPY(&hdr->dipaddr, ipdst_addr, sizeof(ip_addr_t));
+
+  hdr->hwtype = htons(HWTYPE_ETHERNET);
+  hdr->proto = htons(ETHTYPE_IP);
+  /* set hwlen and protolen together */
+  hdr->_hwlen_protolen = htons((ETHARP_HWADDR_LEN << 8) | sizeof(ip_addr_t));
+
+  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, ip_addr_t *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);
+}
+#endif /* LWIP_ARP */
+
+/**
+ * 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 = (struct eth_hdr *)p->payload;
+  LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE,
+    ("ethernet_input: dest:%"X8_F":%"X8_F":%"X8_F":%"X8_F":%"X8_F":%"X8_F", src:%"X8_F":%"X8_F":%"X8_F":%"X8_F":%"X8_F":%"X8_F", type:%"X16_F"\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) {
+#if LWIP_ARP
+    /* IP packet? */
+    case ETHTYPE_IP:
+      if (!(netif->flags & NETIF_FLAG_ETHARP)) {
+        goto free_and_return;
+      }
+#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);
+        goto free_and_return;
+      } else {
+        /* pass to IP layer */
+        ip_input(p, netif);
+      }
+      break;
+      
+    case ETHTYPE_ARP:
+      if (!(netif->flags & NETIF_FLAG_ETHARP)) {
+        goto free_and_return;
+      }
+      /* pass p to ARP module */
+      etharp_arp_input(netif, (struct eth_addr*)(netif->hwaddr), p);
+      break;
+#endif /* LWIP_ARP */
+#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);
+      goto free_and_return;
+  }
+
+  /* This means the pbuf is freed or consumed,
+     so the caller doesn't have to free it again */
+  return ERR_OK;
+
+free_and_return:
+  pbuf_free(p);
+  return ERR_OK;
+}
+#endif /* LWIP_ARP || LWIP_ETHERNET */