--- a/RELEASE_NOTES	Tue Jan 21 23:06:22 2014 +0100
+++ b/RELEASE_NOTES	Thu Jan 23 19:31:42 2014 +0100
@@ -31,6 +31,7 @@
 ----------
 - Bug 1739 - The endpoint is not deallocated for UDP sockets
 - Bug 1786 - os << int64x64_t prints un-normalized fractional values
+- Bug 1808: FlowMon relies on IPv4's Identification field to trace packets
 - Bug 1821 - Setting an interface to Down state will cause various asserts in IPv6
 - Bug 1837 - AODV crashes when using multiple interfaces
 - Bug 1838 - FlowMonitorHelper must not be copied.

--- a/src/flow-monitor/model/ipv4-flow-classifier.cc	Tue Jan 21 23:06:22 2014 +0100
+++ b/src/flow-monitor/model/ipv4-flow-classifier.cc	Thu Jan 23 19:31:42 2014 +0100
@@ -159,11 +159,17 @@
   // if the insertion succeeded, we need to assign this tuple a new flow identifier
   if (insert.second)
     {
-      insert.first->second = GetNewFlowId ();
+      FlowId newFlowId = GetNewFlowId ();
+      insert.first->second = newFlowId;
+      m_flowPktIdMap[newFlowId] = 0;
+    }
+  else
+    {
+      m_flowPktIdMap[insert.first->second] ++;
     }
 
   *out_flowId = insert.first->second;
-  *out_packetId = ipHeader.GetIdentification ();
+  *out_packetId = m_flowPktIdMap[*out_flowId];
 
   return true;
 }

--- a/src/flow-monitor/model/ipv4-flow-classifier.h	Tue Jan 21 23:06:22 2014 +0100
+++ b/src/flow-monitor/model/ipv4-flow-classifier.h	Thu Jan 23 19:31:42 2014 +0100
@@ -52,6 +52,9 @@
   Ipv4FlowClassifier ();
 
   /// \brief try to classify the packet into flow-id and packet-id
+  ///
+  /// \warning: it must be called only once per packet, from SendOutgoingLogger.
+  ///
   /// \return true if the packet was classified, false if not (i.e. it
   /// does not appear to be part of a flow).
   /// \param ipHeader packet's IP header
@@ -72,6 +75,7 @@
 
   /// Map to Flows Identifiers to FlowIds
   std::map<FiveTuple, FlowId> m_flowMap;
+  std::map<FlowId, FlowPacketId> m_flowPktIdMap;
 
 };
 

--- a/src/flow-monitor/model/ipv4-flow-probe.cc	Tue Jan 21 23:06:22 2014 +0100
+++ b/src/flow-monitor/model/ipv4-flow-probe.cc	Thu Jan 23 19:31:42 2014 +0100
@@ -260,31 +260,35 @@
 void
 Ipv4FlowProbe::ForwardLogger (const Ipv4Header &ipHeader, Ptr<const Packet> ipPayload, uint32_t interface)
 {
-  FlowId flowId;
-  FlowPacketId packetId;
+  // peek the tags that are added by Ipv4FlowProbe::SendOutgoingLogger ()
+  Ipv4FlowProbeTag fTag;
+
+  bool found = ipPayload->PeekPacketTag (fTag);
 
-  if (m_classifier->Classify (ipHeader, ipPayload, &flowId, &packetId))
+  if (found)
     {
+      FlowId flowId = fTag.GetFlowId ();
+      FlowPacketId packetId = fTag.GetPacketId ();
+
       uint32_t size = (ipPayload->GetSize () + ipHeader.GetSerializedSize ());
       NS_LOG_DEBUG ("ReportForwarding ("<<this<<", "<<flowId<<", "<<packetId<<", "<<size<<");");
       m_flowMonitor->ReportForwarding (this, flowId, packetId, size);
     }
-
 }
 
 void
 Ipv4FlowProbe::ForwardUpLogger (const Ipv4Header &ipHeader, Ptr<const Packet> ipPayload, uint32_t interface)
 {
-  FlowId flowId;
-  FlowPacketId packetId;
+  // remove the tags that are added by Ipv4FlowProbe::SendOutgoingLogger ()
+  Ipv4FlowProbeTag fTag;
 
-  if (m_classifier->Classify (ipHeader, ipPayload, &flowId, &packetId))
+  // ConstCast: see http://www.nsnam.org/bugzilla/show_bug.cgi?id=904
+  bool found = ConstCast<Packet> (ipPayload)->RemovePacketTag (fTag);
+
+  if (found)
     {
-      // remove the tags that are added by Ipv4FlowProbe::SendOutgoingLogger ()
-      Ipv4FlowProbeTag fTag;
-
-      // ConstCast: see http://www.nsnam.org/bugzilla/show_bug.cgi?id=904
-      ConstCast<Packet> (ipPayload)->RemovePacketTag (fTag);
+      FlowId flowId = fTag.GetFlowId ();
+      FlowPacketId packetId = fTag.GetPacketId ();
 
       uint32_t size = (ipPayload->GetSize () + ipHeader.GetSerializedSize ());
       NS_LOG_DEBUG ("ReportLastRx ("<<this<<", "<<flowId<<", "<<packetId<<", "<<size<<");");
@@ -314,16 +318,16 @@
     }
 #endif
 
-  FlowId flowId;
-  FlowPacketId packetId;
+  // remove the tags that are added by Ipv4FlowProbe::SendOutgoingLogger ()
+  Ipv4FlowProbeTag fTag;
 
-  if (m_classifier->Classify (ipHeader, ipPayload, &flowId, &packetId))
+  // ConstCast: see http://www.nsnam.org/bugzilla/show_bug.cgi?id=904
+  bool found = ConstCast<Packet> (ipPayload)->RemovePacketTag (fTag);
+
+  if (found)
     {
-      // remove the tags that are added by Ipv4FlowProbe::SendOutgoingLogger ()
-      Ipv4FlowProbeTag fTag;
-
-      // ConstCast: see http://www.nsnam.org/bugzilla/show_bug.cgi?id=904
-      ConstCast<Packet> (ipPayload)->RemovePacketTag (fTag);
+      FlowId flowId = fTag.GetFlowId ();
+      FlowPacketId packetId = fTag.GetPacketId ();
 
       uint32_t size = (ipPayload->GetSize () + ipHeader.GetSerializedSize ());
       NS_LOG_DEBUG ("Drop ("<<this<<", "<<flowId<<", "<<packetId<<", "<<size<<", " << reason 
@@ -376,8 +380,7 @@
   Ipv4FlowProbeTag fTag;
 
   // ConstCast: see http://www.nsnam.org/bugzilla/show_bug.cgi?id=904
-  bool tagFound;
-  tagFound = ConstCast<Packet> (ipPayload)->RemovePacketTag (fTag);
+  bool tagFound = ConstCast<Packet> (ipPayload)->RemovePacketTag (fTag);
   if (!tagFound)
     {
       return;