fixed bug #34617: Stable etharp entries that are about to expire are now refreshed using unicast to prevent unnecessary broadcast.

Only if no answer is received after 15 seconds, broadcast is used.

CHANGELOG

@@ -6,6 +6,11 @@ HISTORY
 
   ++ New features:
 
+  2015-03-23: Simon Goldschmidt
+  * etharp.c: Stable etharp entries that are about to expire are now refreshed
+    using unicast to prevent unnecessary broadcast. Only if no answer is received
+    after 15 seconds, broadcast is used.
+
   2015-03-06: Philip Gladstone
   * netif.h/.c: patch #8359 (Provide utility function to add an IPv6 address to
     an interface)

src/netif/etharp.c

@@ -80,7 +80,8 @@ const struct eth_addr ethzero = {{0,0,0,0,0,0}};
 #define ARP_MAXAGE              1200
 /** Re-request a used ARP entry 1 minute before it would expire to prevent
  *  breaking a steadily used connection because the ARP entry timed out. */
-#define ARP_AGE_REREQUEST_USED  (ARP_MAXAGE - 60)
+#define ARP_AGE_REREQUEST_USED_UNICAST   (ARP_MAXAGE - 30)
+#define ARP_AGE_REREQUEST_USED_BROADCAST (ARP_MAXAGE - 15)
 
 /** the time an ARP entry stays pending after first request,
  *  for ARP_TMR_INTERVAL = 1000, this is
@@ -97,7 +98,8 @@ enum etharp_state {
   ETHARP_STATE_EMPTY = 0,
   ETHARP_STATE_PENDING,
   ETHARP_STATE_STABLE,
-  ETHARP_STATE_STABLE_REREQUESTING
+  ETHARP_STATE_STABLE_REREQUESTING_1,
+  ETHARP_STATE_STABLE_REREQUESTING_2
 #if ETHARP_SUPPORT_STATIC_ENTRIES
   ,ETHARP_STATE_STATIC
 #endif /* ETHARP_SUPPORT_STATIC_ENTRIES */
@@ -146,6 +148,9 @@ static u8_t etharp_cached_entry;
 #endif
 
 
+static err_t etharp_request_dst(struct netif *netif, const ip_addr_t *ipaddr, const struct eth_addr* hw_dst_addr);
+
+
 #if ARP_QUEUEING
 /**
  * Free a complete queue of etharp entries
@@ -200,7 +205,7 @@ etharp_free_entry(int i)
 /**
  * Clears expired entries in the ARP table.
  *
- * This function should be called every ETHARP_TMR_INTERVAL milliseconds (5 seconds),
+ * This function should be called every ARP_TMR_INTERVAL milliseconds (1 second),
  * in order to expire entries in the ARP table.
  */
 void
@@ -226,8 +231,10 @@ etharp_tmr(void)
              arp_table[i].state >= ETHARP_STATE_STABLE ? "stable" : "pending", (u16_t)i));
         /* clean up entries that have just been expired */
         etharp_free_entry(i);
-      }
-      else if (arp_table[i].state == ETHARP_STATE_STABLE_REREQUESTING) {
+      } else if (arp_table[i].state == ETHARP_STATE_STABLE_REREQUESTING_1) {
+        /* Don't send more than one request every 2 seconds. */
+        arp_table[i].state = ETHARP_STATE_STABLE_REREQUESTING_2;
+      } else if (arp_table[i].state == ETHARP_STATE_STABLE_REREQUESTING_2) {
         /* Reset state to stable, so that the next transmitted packet will
            re-send an ARP request. */
         arp_table[i].state = ETHARP_STATE_STABLE;
@@ -863,10 +870,17 @@ etharp_output_to_arp_index(struct netif *netif, struct pbuf *q, u8_t arp_idx)
   /* if arp table entry is about to expire: re-request it,
      but only if its state is ETHARP_STATE_STABLE to prevent flooding the
      network with ARP requests if this address is used frequently. */
-  if ((arp_table[arp_idx].state == ETHARP_STATE_STABLE) && 
-      (arp_table[arp_idx].ctime >= ARP_AGE_REREQUEST_USED)) {
-    if (etharp_request(netif, &arp_table[arp_idx].ipaddr) == ERR_OK) {
-      arp_table[arp_idx].state = ETHARP_STATE_STABLE_REREQUESTING;
+  if (arp_table[arp_idx].state == ETHARP_STATE_STABLE) {
+    if (arp_table[arp_idx].ctime >= ARP_AGE_REREQUEST_USED_BROADCAST) {
+      /* issue a standard request using broadcast */
+      if (etharp_request(netif, &arp_table[arp_idx].ipaddr) == ERR_OK) {
+        arp_table[arp_idx].state = ETHARP_STATE_STABLE_REREQUESTING_1;
+      }
+    } else if (arp_table[arp_idx].ctime >= ARP_AGE_REREQUEST_USED_UNICAST) {
+      /* issue a unicast request (for 15 seconds) to prevent unnecessary broadcast */
+      if (etharp_request_dst(netif, &arp_table[arp_idx].ipaddr, &arp_table[arp_idx].ethaddr) == ERR_OK) {
+        arp_table[arp_idx].state = ETHARP_STATE_STABLE_REREQUESTING_1;
+      }
     }
   }
   
@@ -1316,6 +1330,26 @@ etharp_raw(struct netif *netif, const struct eth_addr *ethsrc_addr,
   return result;
 }
 
+/**
+ * Send an ARP request packet asking for ipaddr to a specific eth address.
+ * Used to send unicast request to refresh the ARP table just before an entry
+ * times out
+ *
+ * @param netif the lwip network interface on which to send the request
+ * @param ipaddr the IP address for which to ask
+ * @param hw_dst_addr the ethernet address to send this packet to
+ * @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
+ */
+static err_t
+etharp_request_dst(struct netif *netif, const ip_addr_t *ipaddr, const struct eth_addr* hw_dst_addr)
+{
+  return etharp_raw(netif, (struct eth_addr *)netif->hwaddr, hw_dst_addr,
+                    (struct eth_addr *)netif->hwaddr, &netif->ip_addr, &ethzero,
+                    ipaddr, ARP_REQUEST);
+}
+
 /**
  * Send an ARP request packet asking for ipaddr.
  *
@@ -1329,9 +1363,7 @@ err_t
 etharp_request(struct netif *netif, const 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);
+  return etharp_request_dst(netif, ipaddr, &ethbroadcast);
 }
 #endif /* LWIP_ARP */