--- a/src/internet-node/ipv4-l3-protocol.cc	Thu Jun 05 01:08:33 2008 +0200
+++ b/src/internet-node/ipv4-l3-protocol.cc	Thu Jun 05 15:56:23 2008 -0700
@@ -30,6 +30,7 @@
 #include "ns3/trace-source-accessor.h"
 #include "ns3/object-vector.h"
 #include "ns3/ipv4-header.h"
+#include "ns3/boolean.h"
 #include "arp-l3-protocol.h"
 
 #include "ipv4-l3-protocol.h"
@@ -57,6 +58,11 @@
                    UintegerValue (64),
                    MakeUintegerAccessor (&Ipv4L3Protocol::m_defaultTtl),
                    MakeUintegerChecker<uint8_t> ())
+    .AddAttribute ("CalcChecksum", "If true, we calculate the checksum of outgoing packets"
+                   " and verify the checksum of incoming packets.",
+                   BooleanValue (false),
+                   MakeBooleanAccessor (&Ipv4L3Protocol::m_calcChecksum),
+                   MakeBooleanChecker ())
     .AddTraceSource ("Tx", "Send ipv4 packet to outgoing interface.",
                    MakeTraceSourceAccessor (&Ipv4L3Protocol::m_txTrace))
     .AddTraceSource ("Rx", "Receive ipv4 packet from incoming interface.",
@@ -464,10 +470,15 @@
       index++;
     }
   Ipv4Header ipHeader;
+  if (m_calcChecksum)
+    {
+      ipHeader.EnableChecksum ();
+    }
   packet->RemoveHeader (ipHeader);
 
   if (!ipHeader.IsChecksumOk ()) 
     {
+      m_dropTrace (packet);
       return;
     }
 
@@ -490,6 +501,11 @@
 
   Ipv4Header ipHeader;
 
+  if (m_calcChecksum)
+    {
+      ipHeader.EnableChecksum ();
+    }
+
   ipHeader.SetSource (source);
   ipHeader.SetDestination (destination);
   ipHeader.SetProtocol (protocol);

--- a/src/internet-node/ipv4-l3-protocol.h	Thu Jun 05 01:08:33 2008 +0200
+++ b/src/internet-node/ipv4-l3-protocol.h	Thu Jun 05 15:56:23 2008 -0700
@@ -191,6 +191,7 @@
   Ipv4InterfaceList m_interfaces;
   uint32_t m_nInterfaces;
   uint8_t m_defaultTtl;
+  bool m_calcChecksum;
   uint16_t m_identification;
   Ptr<Node> m_node;
   TracedCallback<Ptr<const Packet>, uint32_t> m_txTrace;

--- a/src/node/ipv4-header.cc	Thu Jun 05 01:08:33 2008 +0200
+++ b/src/node/ipv4-header.cc	Thu Jun 05 15:56:23 2008 -0700
@@ -29,10 +29,9 @@
 
 NS_OBJECT_ENSURE_REGISTERED (Ipv4Header);
 
-bool Ipv4Header::m_calcChecksum = false;
-
 Ipv4Header::Ipv4Header ()
-  : m_payloadSize (0),
+  : m_calcChecksum (false),
+    m_payloadSize (0),
     m_identification (0),
     m_tos (0),
     m_ttl (0),
@@ -43,7 +42,7 @@
 {}
 
 void 
-Ipv4Header::EnableChecksums (void)
+Ipv4Header::EnableChecksum (void)
 {
   m_calcChecksum = true;
 }

--- a/src/node/ipv4-header.h	Thu Jun 05 01:08:33 2008 +0200
+++ b/src/node/ipv4-header.h	Thu Jun 05 15:56:23 2008 -0700
@@ -36,9 +36,9 @@
    */
   Ipv4Header ();
   /**
-   * \brief Enable checksum calculation for IP (XXX currently has no effect)
+   * \brief Enable checksum calculation for this header.
    */
-  static void EnableChecksums (void);
+  void EnableChecksum (void);
   /**
    * \param size the size of the payload in bytes
    */
@@ -134,7 +134,7 @@
    * \returns true if the ipv4 checksum is correct, false otherwise.
    *
    * If Ipv4Header::EnableChecksums has not been called prior to
-   * creating this packet, this method will always return true.
+   * deserializing this header, this method will always return true.
    */
   bool IsChecksumOk (void) const;
 
@@ -152,7 +152,7 @@
     MORE_FRAGMENTS = (1<<1)
   };
 
-  static bool m_calcChecksum;
+  bool m_calcChecksum;
 
   uint16_t m_payloadSize;
   uint16_t m_identification;