diff --git a/model/forwarding-strategy/nacks.h b/model/forwarding-strategy/nacks.h
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+++ b/model/forwarding-strategy/nacks.h
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+/* -*- 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>
+ */
+#ifndef NDNSIM_NACKS_H
+#define NDNSIM_NACKS_H
+
+#include "ns3/ccnx-forwarding-strategy.h"
+
+namespace ns3 {
+
+namespace ndnSIM {
+
+/**
+ * \ingroup ccnx
+ * \brief Abstract base class for CCNx forwarding strategies
+ */
+class Nacks :
+    public CcnxForwardingStrategy
+{
+public:
+  static TypeId
+  GetTypeId (void);
+
+  /**
+   * \brief Actual processing of incoming CCNx interests. Note, interests do not have payload
+   * 
+   * Processing Interest packets
+   * @param face    incoming face
+   * @param header  deserialized Interest header
+   * @param packet  original packet
+   */
+  virtual void
+  OnInterest (const Ptr<CcnxFace> &face,
+              Ptr<CcnxInterestHeader> &header,
+              const Ptr<const Packet> &p);
+
+protected:
+  // using CcnxForwardingStrategy::PropagateInterest; // some strange c++ cheating
+
+  virtual void
+  DidReceiveDuplicateInterest (const Ptr<CcnxFace> &face,
+                               Ptr<CcnxInterestHeader> &header,
+                               const Ptr<const Packet> &packet,
+                               Ptr<CcnxPitEntry> pitEntry);
+  
+  virtual void
+  DidExhaustForwardingOptions (const Ptr<CcnxFace> &incomingFace,
+                               Ptr<CcnxInterestHeader> header,
+                               const Ptr<const Packet> &packet,
+                               Ptr<CcnxPitEntry> pitEntry);
+
+  virtual void
+  OnNack (const Ptr<CcnxFace> &face,
+          Ptr<CcnxInterestHeader> &header,
+          const Ptr<const Packet> &p);
+
+  // virtual void
+  // OnDataDelayed (Ptr<const CcnxContentObjectHeader> header,
+  //                Ptr<const Packet> payload,
+  //                const Ptr<const Packet> &packet);
+  
+protected:  
+  bool m_nacksEnabled;
+
+  TracedCallback<Ptr<const CcnxInterestHeader>,
+                 Ptr<const CcnxFace> > m_outNacks; ///< @brief trace of outgoing NACKs
+
+  TracedCallback<Ptr<const CcnxInterestHeader>,
+                 Ptr<const CcnxFace> > m_inNacks; ///< @brief trace of incoming NACKs
+
+  TracedCallback<Ptr<const CcnxInterestHeader>,
+                 Ptr<const CcnxFace> > m_dropNacks; ///< @brief trace of dropped NACKs
+
+private:
+  typedef CcnxForwardingStrategy super;
+};
+
+} // namespace ndnSIM
+} // namespace ns3
+
+#endif // NDNSIM_NACKS