diff -r 509c35cf49ae examples/csma-one-subnet.cc
--- a/examples/csma-one-subnet.cc	Sun May 25 05:35:22 2008 -0700
+++ b/examples/csma-one-subnet.cc	Sun May 25 09:51:23 2008 -0700
@@ -80,6 +80,7 @@ main (int argc, char *argv[])
   NetDeviceContainer nd0 = csma.Install (c);
 
   InternetStackHelper internet;
+  internet.UseGodArp ();
   internet.Install (c);
 
 // We've got the "hardware" in place.  Now we need to add IP addresses.
diff -r 509c35cf49ae src/helper/internet-stack-helper.cc
--- a/src/helper/internet-stack-helper.cc	Sun May 25 05:35:22 2008 -0700
+++ b/src/helper/internet-stack-helper.cc	Sun May 25 09:53:40 2008 -0700
@@ -47,6 +47,22 @@ InternetStackHelper::Cleanup (void)
   m_traces.clear ();
 }
 
+InternetStackHelper::InternetStackHelper ()
+  : m_godArp (false)
+{}
+
+void 
+InternetStackHelper::UseGodArp (void)
+{
+  m_godArp = true;
+}
+void 
+InternetStackHelper::UseRealArp (void)
+{
+  m_godArp = false;
+}
+
+
 void 
 InternetStackHelper::Install (NodeContainer c)
 {
@@ -58,8 +74,19 @@ InternetStackHelper::Install (NodeContai
           NS_FATAL_ERROR ("InternetStackHelper::Install(): Aggregating " 
              "an InternetStack to a node with an existing Ipv4 object");
           return;
-        } 
-      AddInternetStack (node);
+        }
+      if (m_godArp)
+        {
+          InternetStack::AddGodArp (node);
+        }
+      else
+        {
+          InternetStack::AddRealArp (node);
+        }
+      InternetStack::AddIpv4 (node);
+      InternetStack::AddUdp (node);
+      InternetStack::AddTcp (node);
+
       Ptr<PacketSocketFactory> factory = CreateObject<PacketSocketFactory> ();
       node->AggregateObject (factory);
     }
diff -r 509c35cf49ae src/helper/internet-stack-helper.h
--- a/src/helper/internet-stack-helper.h	Sun May 25 05:35:22 2008 -0700
+++ b/src/helper/internet-stack-helper.h	Sun May 25 09:27:12 2008 -0700
@@ -33,6 +33,22 @@ class InternetStackHelper
 class InternetStackHelper
 {
 public:
+  InternetStackHelper ();
+  /**
+   * Every internet stack created with Install after calling this 
+   * method will contain a 'God' ARP implementation.
+   *
+   * \sa ns3::GodArp
+   */
+  void UseGodArp (void);
+  /*
+   * Every internet stack created with Install after calling this 
+   * method will contain a 'Real' ARP implementation.
+   *
+   * \sa ns3::Ipv4L3Protocol
+   */
+  void UseRealArp (void);
+
   /**
    * \param c the set of nodes
    *
@@ -72,6 +88,7 @@ private:
   static std::string m_pcapBaseFilename;
   static uint32_t GetNodeIndex (std::string context);
   static std::vector<Trace> m_traces;
+  bool m_godArp;
 };
 
 } // namespace ns3
diff -r 509c35cf49ae src/internet-node/arp-ipv4-interface.cc
--- a/src/internet-node/arp-ipv4-interface.cc	Sun May 25 05:35:22 2008 -0700
+++ b/src/internet-node/arp-ipv4-interface.cc	Sun May 25 09:05:17 2008 -0700
@@ -76,8 +76,8 @@ ArpIpv4Interface::SendTo (Ptr<Packet> p,
   if (GetDevice ()->NeedsArp ())
     {
       NS_LOG_LOGIC ("Needs ARP");
-      Ptr<ArpL3Protocol> arp = 
-        m_node->GetObject<ArpL3Protocol> ();
+      Ptr<Arp> arp = 
+        m_node->GetObject<Arp> ();
       Address hardwareDestination;
       bool found;
       
diff -r 509c35cf49ae src/internet-node/arp-l3-protocol.cc
--- a/src/internet-node/arp-l3-protocol.cc	Sun May 25 05:35:22 2008 -0700
+++ b/src/internet-node/arp-l3-protocol.cc	Sun May 25 09:00:59 2008 -0700
@@ -40,7 +40,7 @@ ArpL3Protocol::GetTypeId (void)
 ArpL3Protocol::GetTypeId (void)
 {
   static TypeId tid = TypeId ("ns3::ArpL3Protocol")
-    .SetParent<Object> ()
+    .SetParent<Arp> ()
     ;
   return tid;
 }
diff -r 509c35cf49ae src/internet-node/arp-l3-protocol.h
--- a/src/internet-node/arp-l3-protocol.h	Sun May 25 05:35:22 2008 -0700
+++ b/src/internet-node/arp-l3-protocol.h	Sun May 25 09:04:15 2008 -0700
@@ -21,6 +21,7 @@
 #define ARP_L3_PROTOCOL_H
 
 #include <list>
+#include "arp.h"
 #include "ns3/ipv4-address.h"
 #include "ns3/address.h"
 #include "ns3/ptr.h"
@@ -35,7 +36,7 @@ class Packet;
 /**
  * \brief An implementation of the ARP protocol
  */
-class ArpL3Protocol : public Object
+class ArpL3Protocol : public Arp
 {
 public:
   static TypeId GetTypeId (void);
@@ -50,17 +51,10 @@ public:
    * \brief Recieve a packet
    */
   void Receive(Ptr<NetDevice> device, Ptr<Packet> p, uint16_t protocol, const Address &from);
-  /**
-   * \brief Perform an ARP lookup
-   * \param p
-   * \param destination
-   * \param device
-   * \param hardwareDestination
-   * \return 
-   */
-  bool Lookup (Ptr<Packet> p, Ipv4Address destination, 
-	       Ptr<NetDevice> device,
-	       Address *hardwareDestination);
+
+  virtual bool Lookup (Ptr<Packet> p, Ipv4Address destination, 
+                       Ptr<NetDevice> device,
+                       Address *hardwareDestination);
 protected:
   virtual void DoDispose (void);
 private:
diff -r 509c35cf49ae src/internet-node/arp.cc
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/internet-node/arp.cc	Sun May 25 09:13:41 2008 -0700
@@ -0,0 +1,36 @@
+/* -*-  Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2006 INRIA
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Author: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>
+ */
+#include "arp.h"
+
+namespace ns3 {
+
+TypeId 
+Arp::GetTypeId (void)
+{
+  static TypeId tid = TypeId ("ns3::Arp")
+    .SetParent<Object> ()
+    ;
+  return tid;
+}
+
+Arp::~Arp ()
+{}
+
+} // namespace ns3
diff -r 509c35cf49ae src/internet-node/arp.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/internet-node/arp.h	Sun May 25 09:02:37 2008 -0700
@@ -0,0 +1,62 @@
+/* -*-  Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2006 INRIA
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Author: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>
+ */
+#ifndef ARP_H
+#define ARP_H
+
+#include <list>
+#include "ns3/object.h"
+#include "ns3/ipv4-address.h"
+#include "ns3/ptr.h"
+
+namespace ns3 {
+
+class NetDevice;
+class Node;
+class Packet;
+class Address;
+
+/**
+ * \brief An interface to access the functionality provided
+ *        by the ARP layer.
+ */
+class Arp : public Object
+{
+public:
+  static TypeId GetTypeId (void);
+
+  virtual ~Arp ();
+
+  /**
+   * \brief Perform an ARP lookup
+   * \param p
+   * \param destination
+   * \param device
+   * \param hardwareDestination
+   * \return 
+   */
+  virtual bool Lookup (Ptr<Packet> p, Ipv4Address destination, 
+                       Ptr<NetDevice> device,
+                       Address *hardwareDestination) = 0;
+};
+
+}//namespace ns3
+
+
+#endif /* ARP_H */
diff -r 509c35cf49ae src/internet-node/god-arp.cc
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/internet-node/god-arp.cc	Sun May 25 09:13:19 2008 -0700
@@ -0,0 +1,66 @@
+/* -*-  Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2008 INRIA
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Author: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>
+ */
+#include "god-arp.h"
+#include "ns3/ipv4.h"
+#include "ns3/channel.h"
+#include "ns3/net-device.h"
+#include "ns3/node.h"
+
+namespace ns3 {
+
+TypeId 
+GodArp::GetTypeId (void)
+{
+  static TypeId tid = TypeId ("ns3::GodArp")
+    .SetParent<Arp> ()
+    ;
+  return tid;
+}
+
+GodArp::GodArp ()
+{}
+  
+bool 
+GodArp::Lookup (Ptr<Packet> p, Ipv4Address destination, 
+		Ptr<NetDevice> device,
+		Address *hardwareDestination)
+{
+  Ptr<Channel> channel = device->GetChannel ();
+  for (uint32_t i = 0; i < channel->GetNDevices (); ++i)
+    {
+      Ptr<NetDevice> remote = channel->GetDevice (i);
+      Ptr<Node> remoteNode = remote->GetNode ();
+      Ptr<Ipv4> remoteIpv4 = remoteNode->GetObject<Ipv4> ();
+      if (remoteIpv4 == 0)
+	{
+	  continue;
+	}
+      int32_t index = remoteIpv4->FindInterfaceForDevice (remote);
+      if (index == -1)
+	{
+	  continue;
+	}
+      *hardwareDestination = remote->GetAddress ();
+      return true;
+    }
+  return false;
+}
+
+} // namespace ns3 
diff -r 509c35cf49ae src/internet-node/god-arp.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/internet-node/god-arp.h	Sun May 25 09:12:23 2008 -0700
@@ -0,0 +1,41 @@
+/* -*-  Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2008 INRIA
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Author: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>
+ */
+#ifndef GOD_ARP_H
+#define GOD_ARP_H
+
+#include "arp.h"
+
+namespace ns3 {
+
+class GodArp : public Arp
+{
+public:
+  static TypeId GetTypeId (void);
+  GodArp ();
+  
+  virtual bool Lookup (Ptr<Packet> p, Ipv4Address destination, 
+                       Ptr<NetDevice> device,
+                       Address *hardwareDestination);
+};
+
+
+} // namespace ns3
+
+#endif /* GOD_ARP_H */
diff -r 509c35cf49ae src/internet-node/internet-stack.cc
--- a/src/internet-node/internet-stack.cc	Sun May 25 05:35:22 2008 -0700
+++ b/src/internet-node/internet-stack.cc	Sun May 25 09:41:58 2008 -0700
@@ -27,51 +27,98 @@
 #include "tcp-l4-protocol.h"
 #include "ipv4-l3-protocol.h"
 #include "arp-l3-protocol.h"
+#include "god-arp.h"
 #include "udp-impl.h"
 #include "tcp-impl.h"
 #include "ipv4-impl.h"
 
 namespace ns3 {
 
+namespace InternetStack {
+
+static Ptr<Ipv4L4Demux>
+AddIpv4L4Demux (Ptr<Node> node)
+{
+
+  Ptr<Ipv4L4Demux> ipv4L4Demux = node->GetObject<Ipv4L4Demux> ();
+  if (ipv4L4Demux != 0)
+    {
+      return ipv4L4Demux;
+    }
+  ipv4L4Demux = CreateObject<Ipv4L4Demux> ();
+  ipv4L4Demux->SetNode (node);
+  node->AggregateObject (ipv4L4Demux);
+  return ipv4L4Demux;
+}
+
+void
+AddTcp (Ptr<Node> node)
+{
+  Ptr<TcpL4Protocol> tcp = CreateObject<TcpL4Protocol> ();
+  tcp->SetNode (node);
+  Ptr<Ipv4L4Demux> ipv4L4Demux = AddIpv4L4Demux (node);
+  ipv4L4Demux->Insert (tcp);
+  Ptr<TcpImpl> tcpImpl = CreateObject<TcpImpl> ();
+  tcpImpl->SetTcp (tcp);
+  node->AggregateObject (tcpImpl);
+}
+
+void
+AddUdp (Ptr<Node> node)
+{
+  Ptr<UdpL4Protocol> udp = CreateObject<UdpL4Protocol> ();
+  udp->SetNode (node);
+  Ptr<Ipv4L4Demux> ipv4L4Demux = AddIpv4L4Demux (node);
+  ipv4L4Demux->Insert (udp);
+  Ptr<UdpImpl> udpImpl = CreateObject<UdpImpl> ();
+  udpImpl->SetUdp (udp);
+  node->AggregateObject (udpImpl);
+}
+
 void 
-AddInternetStack (Ptr<Node> node)
+AddIpv4 (Ptr<Node> node)
 {
   Ptr<Ipv4L3Protocol> ipv4 = CreateObject<Ipv4L3Protocol> ();
-  Ptr<ArpL3Protocol> arp = CreateObject<ArpL3Protocol> ();
   ipv4->SetNode (node);
-  arp->SetNode (node);
   // XXX remove the PeekPointer below.
   node->RegisterProtocolHandler (MakeCallback (&Ipv4L3Protocol::Receive, PeekPointer (ipv4)), 
                                  Ipv4L3Protocol::PROT_NUMBER, 0);
-  node->RegisterProtocolHandler (MakeCallback (&ArpL3Protocol::Receive, PeekPointer (arp)),
-                                 ArpL3Protocol::PROT_NUMBER, 0);
 
-
-  Ptr<Ipv4L4Demux> ipv4L4Demux = CreateObject<Ipv4L4Demux> ();
-  Ptr<UdpL4Protocol> udp = CreateObject<UdpL4Protocol> ();
-  Ptr<TcpL4Protocol> tcp = CreateObject<TcpL4Protocol> ();
-
-  ipv4L4Demux->SetNode (node);
-  udp->SetNode (node);
-  tcp->SetNode (node);
-
-  ipv4L4Demux->Insert (udp);
-  ipv4L4Demux->Insert (tcp);
-
-  Ptr<UdpImpl> udpImpl = CreateObject<UdpImpl> ();
-  Ptr<TcpImpl> tcpImpl = CreateObject<TcpImpl> ();
   Ptr<Ipv4Impl> ipv4Impl = CreateObject<Ipv4Impl> ();
-
-  udpImpl->SetUdp (udp);
-  tcpImpl->SetTcp (tcp);
   ipv4Impl->SetIpv4 (ipv4);
 
   node->AggregateObject (ipv4);
-  node->AggregateObject (arp);
   node->AggregateObject (ipv4Impl);
-  node->AggregateObject (udpImpl);
-  node->AggregateObject (tcpImpl);
-  node->AggregateObject (ipv4L4Demux);
 }
 
+void 
+AddGodArp (Ptr<Node> node)
+{
+  Ptr<Arp> arp = CreateObject<GodArp> ();
+  node->AggregateObject (arp);
+}
+
+void 
+AddRealArp (Ptr<Node> node)
+{
+  // XXX remove the PeekPointer below.
+  Ptr<ArpL3Protocol> arp = CreateObject<ArpL3Protocol> ();
+  arp->SetNode (node);
+  node->RegisterProtocolHandler (MakeCallback (&ArpL3Protocol::Receive, PeekPointer (arp)),
+                                 ArpL3Protocol::PROT_NUMBER, 0);
+  node->AggregateObject (arp);
+}
+
+void 
+AddAll (Ptr<Node> node)
+{
+  AddRealArp (node);
+  AddIpv4 (node);
+  AddUdp (node);
+  AddTcp (node);
+}
+
+
+} // namespace InternetStack
+
 }//namespace ns3
diff -r 509c35cf49ae src/internet-node/internet-stack.h
--- a/src/internet-node/internet-stack.h	Sun May 25 05:35:22 2008 -0700
+++ b/src/internet-node/internet-stack.h	Sun May 25 09:29:21 2008 -0700
@@ -26,7 +26,16 @@ namespace ns3 {
 
 class Node;
 
-void AddInternetStack (Ptr<Node> node);
+namespace InternetStack {
+
+void AddAll (Ptr<Node> node);
+void AddGodArp (Ptr<Node> node);
+void AddRealArp (Ptr<Node> node);
+void AddIpv4 (Ptr<Node> node);
+void AddUdp (Ptr<Node> node);
+void AddTcp (Ptr<Node> node);
+
+} // namespace InternetStack
 
 }//namespace ns3
 
diff -r 509c35cf49ae src/internet-node/udp-socket.cc
--- a/src/internet-node/udp-socket.cc	Sun May 25 05:35:22 2008 -0700
+++ b/src/internet-node/udp-socket.cc	Sun May 25 09:31:01 2008 -0700
@@ -393,7 +393,7 @@ UdpSocketTest::RunTests (void)
   
   // Receiver Node
   Ptr<Node> rxNode = CreateObject<Node> ();
-  AddInternetStack (rxNode);
+  InternetStack::AddAll (rxNode);
   Ptr<SimpleNetDevice> rxDev1, rxDev2;
   { // first interface
     rxDev1 = CreateObject<SimpleNetDevice> ();
@@ -419,7 +419,7 @@ UdpSocketTest::RunTests (void)
   
   // Sender Node
   Ptr<Node> txNode = CreateObject<Node> ();
-  AddInternetStack (txNode);
+  InternetStack::AddAll (txNode);
   Ptr<SimpleNetDevice> txDev1;
   {
     txDev1 = CreateObject<SimpleNetDevice> ();
diff -r 509c35cf49ae src/internet-node/wscript
--- a/src/internet-node/wscript	Sun May 25 05:35:22 2008 -0700
+++ b/src/internet-node/wscript	Sun May 25 09:12:35 2008 -0700
@@ -17,6 +17,8 @@ def build(bld):
         'ipv4-end-point.cc',
         'udp-l4-protocol.cc',
         'tcp-l4-protocol.cc',
+        'arp.cc',
+        'god-arp.cc',
         'arp-header.cc',
         'arp-cache.cc',
         'arp-ipv4-interface.cc',