From 40d25adb884279ee3968c55c741921e2f2109f7a Mon Sep 17 00:00:00 2001
From: goldsimon <goldsimon@gmx.de>
Date: Mon, 17 Mar 2014 12:53:31 +0100
Subject: [PATCH] Added LWIP_HOOK_ETHARP_GET_GW to implement IPv4 routing with
 multiple gateways

---
 CHANGELOG              |  4 ++++
 src/include/lwip/opt.h | 13 +++++++++++++
 src/netif/etharp.c     | 24 ++++++++++++++++--------
 3 files changed, 33 insertions(+), 8 deletions(-)

diff --git a/CHANGELOG b/CHANGELOG
index 6db4c834..f86f5d9b 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -6,6 +6,10 @@ HISTORY
 
  ++ New features:
 
+  2013-03-17: Simon Goldschmidt (patch by Ghobad Emadi)
+  * opt.h, etharp.c: Added LWIP_HOOK_ETHARP_GET_GW to implement IPv4 routing with
+    multiple gateways
+
   2013-04-20: Fatih Asici
   * opt.h, etharp.h/.c: patch #7993: Added support for transmitting packets
     with VLAN headers via hook function LWIP_HOOK_VLAN_SET and to check them
diff --git a/src/include/lwip/opt.h b/src/include/lwip/opt.h
index 7db6b4ad..11080be5 100644
--- a/src/include/lwip/opt.h
+++ b/src/include/lwip/opt.h
@@ -2235,6 +2235,19 @@
  * that case, ip_route() continues as normal.
  */
 
+/**
+ * LWIP_HOOK_ETHARP_GET_GW(netif, dest):
+ * - called from etharp_output() (IPv4)
+ * - netif: the netif used for sending
+ * - dest: the destination IPv4 address
+ * Returns the IPv4 address of the gateway to handle the specified destination
+ * IPv4 address. If NULL is returned, the netif's default gateway is used.
+ * The returned address MUST be reachable on the specified netif!
+ * This function is meant to implement advanced IPv4 routing together with
+ * LWIP_HOOK_IP4_ROUTE(). The actual routing/gateway table implementation is
+ * not part of lwIP but can e.g. be hidden in the netif's state argument.
+*/
+
 /**
  * LWIP_HOOK_VLAN_CHECK(netif, eth_hdr, vlan_hdr):
  * - called from ethernet_input() if VLAN support is enabled
diff --git a/src/netif/etharp.c b/src/netif/etharp.c
index a3aff06a..650af4c7 100644
--- a/src/netif/etharp.c
+++ b/src/netif/etharp.c
@@ -954,14 +954,22 @@ etharp_output(struct netif *netif, struct pbuf *q, ip_addr_t *ipaddr)
       if (!ip_addr_islinklocal(&iphdr->src))
 #endif /* LWIP_AUTOIP */
       {
-        /* interface has default gateway? */
-        if (!ip_addr_isany(&netif->gw)) {
-          /* send to hardware address of default gateway IP address */
-          dst_addr = &(netif->gw);
-        /* no default gateway available */
-        } else {
-          /* no route to destination error (default gateway missing) */
-          return ERR_RTE;
+#ifdef LWIP_HOOK_ETHARP_GET_GW
+        /* For advanced routing, a single default gateway might not be enough, so get
+           the IP address of the gateway to handle the current destination address. */
+        dst_addr = LWIP_HOOK_ETHARP_GET_GW(netif, ipaddr);
+        if(dst_addr == NULL)
+#endif /* LWIP_HOOK_ETHARP_GET_GW */
+        {
+          /* interface has default gateway? */
+          if (!ip_addr_isany(&netif->gw)) {
+            /* send to hardware address of default gateway IP address */
+            dst_addr = &(netif->gw);
+          /* no default gateway available */
+          } else {
+            /* no route to destination error (default gateway missing) */
+            return ERR_RTE;
+          }
         }
       }
     }