diff --git a/model/fw/nacks.cc b/model/fw/nacks.cc
new file mode 100644
index 0000000..a148794
--- /dev/null
+++ b/model/fw/nacks.cc
@@ -0,0 +1,203 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil -*- */
+/*
+ * Copyright (c) 2011 University of California, Los Angeles
+ *
+ * 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:  Alexander Afanasyev <alexander.afanasyev@ucla.edu>
+ */
+
+#include "nacks.h"
+
+#include "ns3/ndn-pit.h"
+#include "ns3/ndn-pit-entry.h"
+#include "ns3/ndn-interest-header.h"
+#include "ns3/ndn-content-object-header.h"
+#include "ns3/ndn-pit.h"
+#include "ns3/ndn-fib.h"
+#include "ns3/ndn-content-store.h"
+
+#include "ns3/assert.h"
+#include "ns3/ptr.h"
+#include "ns3/log.h"
+#include "ns3/simulator.h"
+#include "ns3/boolean.h"
+#include "ns3/string.h"
+
+#include <boost/ref.hpp>
+#include <boost/foreach.hpp>
+#include <boost/lambda/lambda.hpp>
+#include <boost/lambda/bind.hpp>
+#include <boost/tuple/tuple.hpp>
+namespace ll = boost::lambda;
+
+NS_LOG_COMPONENT_DEFINE ("ndn.fw.Nacks");
+
+namespace ns3 {
+namespace ndn {
+namespace fw {
+
+NS_OBJECT_ENSURE_REGISTERED (Nacks);
+
+TypeId
+Nacks::GetTypeId (void)
+{
+  static TypeId tid = TypeId ("ns3::ndn::fw::Nacks")
+    .SetGroupName ("Ndn")
+    .SetParent<ForwardingStrategy> ()
+    
+    ////////////////////////////////////////////////////////////////////
+    ////////////////////////////////////////////////////////////////////
+
+    .AddTraceSource ("OutNacks",  "OutNacks",  MakeTraceSourceAccessor (&Nacks::m_outNacks))
+    .AddTraceSource ("InNacks",   "InNacks",   MakeTraceSourceAccessor (&Nacks::m_inNacks))
+    .AddTraceSource ("DropNacks", "DropNacks", MakeTraceSourceAccessor (&Nacks::m_dropNacks))
+    
+    .AddAttribute ("EnableNACKs", "Enabling support of NACKs",
+                   BooleanValue (false),
+                   MakeBooleanAccessor (&Nacks::m_nacksEnabled),
+                   MakeBooleanChecker ())
+    ;
+  return tid;
+}
+
+void
+Nacks::OnInterest (const Ptr<Face> &incomingFace,
+                   Ptr<InterestHeader> &header,
+                   const Ptr<const Packet> &packet)
+{
+  if (header->GetNack () > 0)
+    OnNack (incomingFace, header, packet/*original packet*/);
+  else
+    super::OnInterest (incomingFace, header, packet/*original packet*/);  
+}
+
+void
+Nacks::OnNack (const Ptr<Face> &incomingFace,
+               Ptr<InterestHeader> &header,
+               const Ptr<const Packet> &packet)
+{
+  NS_ASSERT (m_nacksEnabled);
+
+  // NS_LOG_FUNCTION (incomingFace << header << packet);
+  m_inNacks (header, incomingFace);
+
+  Ptr<pit::Entry> pitEntry = m_pit->Lookup (*header);
+  if (pitEntry == 0)
+    {
+      // somebody is doing something bad
+      m_dropNacks (header, incomingFace);
+      return;
+    }
+  
+  // This was done in error. Never, never do anything, except normal leakage. This way we ensure that we will not have losses,
+  // at least when there is only one client
+  //
+  // incomingFace->LeakBucketByOnePacket ();
+
+  pitEntry->SetWaitingInVain (incomingFace);
+
+  DidReceiveValidNack (incomingFace, header->GetNack (), pitEntry);
+  
+  if (!pitEntry->AreAllOutgoingInVain ()) // not all ougtoing are in vain
+    {
+      NS_LOG_DEBUG ("Not all outgoing are in vain");
+      // suppress
+      // Don't do anything, we are still expecting data from some other face
+      m_dropNacks (header, incomingFace);
+      return;
+    }
+  
+  Ptr<Packet> nonNackInterest = Create<Packet> ();
+  header->SetNack (InterestHeader::NORMAL_INTEREST);
+  nonNackInterest->AddHeader (*header);
+  
+  bool propagated = DoPropagateInterest (incomingFace, header, nonNackInterest, pitEntry);
+  if (!propagated)
+    {
+      DidExhaustForwardingOptions (incomingFace, header, nonNackInterest, pitEntry);
+    }  
+}
+
+void
+Nacks::DidReceiveDuplicateInterest (const Ptr<Face> &incomingFace,
+                                    Ptr<InterestHeader> &header,
+                                    const Ptr<const Packet> &packet,
+                                    Ptr<pit::Entry> pitEntry)
+{
+  super::DidReceiveDuplicateInterest (incomingFace, header, packet, pitEntry);
+
+  if (m_nacksEnabled)
+    {
+      NS_LOG_DEBUG ("Sending NACK_LOOP");
+      header->SetNack (InterestHeader::NACK_LOOP);
+      Ptr<Packet> nack = Create<Packet> ();
+      nack->AddHeader (*header);
+
+      incomingFace->Send (nack);
+      m_outNacks (header, incomingFace);
+    }
+}
+
+void
+Nacks::DidExhaustForwardingOptions (const Ptr<Face> &incomingFace,
+                                    Ptr<InterestHeader> header,
+                                    const Ptr<const Packet> &packet,
+                                    Ptr<pit::Entry> pitEntry)
+{
+  super::DidExhaustForwardingOptions (incomingFace, header, packet, pitEntry);
+
+  if (m_nacksEnabled)
+    {
+      Ptr<Packet> packet = Create<Packet> ();
+      header->SetNack (InterestHeader::NACK_GIVEUP_PIT);
+      packet->AddHeader (*header);
+
+      BOOST_FOREACH (const pit::IncomingFace &incoming, pitEntry->GetIncoming ())
+        {
+          NS_LOG_DEBUG ("Send NACK for " << boost::cref (header->GetName ()) << " to " << boost::cref (*incoming.m_face));
+          incoming.m_face->Send (packet->Copy ());
+
+          m_outNacks (header, incoming.m_face);
+        }
+  
+      // All incoming interests cannot be satisfied. Remove them
+      pitEntry->ClearIncoming ();
+
+      // Remove also outgoing
+      pitEntry->ClearOutgoing ();
+  
+      // Set pruning timout on PIT entry (instead of deleting the record)
+      m_pit->MarkErased (pitEntry);
+    }  
+}
+
+void
+Nacks::DidReceiveValidNack (const Ptr<Face> &incomingFace,
+                            uint32_t nackCode,
+                            Ptr<pit::Entry> pitEntry)
+{
+  // If NACK is NACK_GIVEUP_PIT, then neighbor gave up trying to and removed it's PIT entry.
+  // So, if we had an incoming entry to this neighbor, then we can remove it now
+  if (nackCode == InterestHeader::NACK_GIVEUP_PIT)
+    {
+      pitEntry->RemoveIncoming (incomingFace);
+    }
+
+  pitEntry->GetFibEntry ()->UpdateStatus (incomingFace, fib::FaceMetric::NDN_FIB_YELLOW);
+}
+
+} // namespace fw
+} // namespace ndn
+} // namespace ns3