diff --git a/model/ccnx-interest-header.cc b/model/ccnx-interest-header.cc
index 323c5fc..d44ac45 100644
--- a/model/ccnx-interest-header.cc
+++ b/model/ccnx-interest-header.cc
@@ -56,6 +56,8 @@
   , m_scope (-1)
   , m_interestLifetime (Seconds (0))
   , m_nonce (0)
+  , m_nack (false)
+  , m_congested (false)
 {
 }
 
@@ -174,7 +176,31 @@
 {
   return m_nonce;
 }
-  
+
+void
+CcnxInterestHeader::SetNack (bool isNack)
+{
+  m_nack = isNack;
+}
+    
+bool
+CcnxInterestHeader::IsNack () const
+{
+  return m_nack;
+}
+ 
+void
+CcnxInterestHeader::SetCongested (bool IsCongested)
+{
+  m_congested = IsCongested;
+}
+    
+bool
+CcnxInterestHeader::IsCongested () const
+{
+  return m_congested;
+}
+
 uint32_t
 CcnxInterestHeader::GetSerializedSize (void) const
 {
@@ -206,6 +232,8 @@
 CcnxInterestHeader::Print (std::ostream &os) const
 {
   os << "<Interest>\n  <Name>" << GetName () << "</Name>\n";
+  if (IsNack ())
+    os << "  <NACK />\n";
   if (GetMinSuffixComponents () >= 0)
     os << "  <MinSuffixComponents>" << GetMinSuffixComponents () << "</MinSuffixComponents>\n";
   if (GetMaxSuffixComponents () >= 0)
diff --git a/model/ccnx-interest-header.h b/model/ccnx-interest-header.h
index 061c26b..4bfebe3 100644
--- a/model/ccnx-interest-header.h
+++ b/model/ccnx-interest-header.h
@@ -201,6 +201,18 @@
 
   uint32_t
   GetNonce () const;
+    
+  void
+  SetNack (bool isNack);
+    
+  bool
+  IsNack () const;
+    
+  void
+  SetCongested (bool IsCongested);
+    
+  bool
+  IsCongested () const;
 
   //////////////////////////////////////////////////////////////////
   
@@ -221,6 +233,8 @@
   int8_t m_scope;            ///< -1 not set, 0 local scope, 1 this host, 2 immediate neighborhood
   Time  m_interestLifetime;
   uint32_t m_nonce; ///< Nonce. not used if zero
+  bool m_nack; ///< is Negative ACK
+  bool m_congested; ///< NACK because of congestion 
 };
 
 class CcnxInterestHeaderException {};