--- a/src/internet-stack/ipv4-l3-protocol.cc	Tue Feb 09 10:40:54 2010 +0100
+++ b/src/internet-stack/ipv4-l3-protocol.cc	Wed Feb 10 11:03:32 2010 +0100
@@ -482,6 +482,7 @@
       socket->ForwardUp (packet, ipHeader, device);
     }
 
+  NS_ASSERT_MSG (m_routingProtocol != 0, "Need a routing protocol object to process packets");
   m_routingProtocol->RouteInput (packet, ipHeader, device, 
     MakeCallback (&Ipv4L3Protocol::IpForward, this),
     MakeCallback (&Ipv4L3Protocol::IpMulticastForward, this),
@@ -609,7 +610,15 @@
   Socket::SocketErrno errno_; 
   Ptr<NetDevice> oif (0); // unused for now
   ipHeader = BuildHeader (source, destination, protocol, packet->GetSize (), ttl, mayFragment);
-  Ptr<Ipv4Route> newRoute = m_routingProtocol->RouteOutput (packet, ipHeader, oif, errno_);
+  Ptr<Ipv4Route> newRoute;
+  if (m_routingProtocol != 0)
+    {
+      newRoute = m_routingProtocol->RouteOutput (packet, ipHeader, oif, errno_);
+    }
+  else
+    {
+      NS_LOG_ERROR ("Ipv4L3Protocol::Send: m_routingProtocol == 0");
+    }
   if (newRoute)
     {
       int32_t interface = GetInterfaceForDevice (newRoute->GetOutputDevice ());

--- a/src/internet-stack/tcp-l4-protocol.cc	Tue Feb 09 10:40:54 2010 +0100
+++ b/src/internet-stack/tcp-l4-protocol.cc	Wed Feb 10 11:03:32 2010 +0100
@@ -584,7 +584,15 @@
       Socket::SocketErrno errno_;
       Ptr<Ipv4Route> route;
       Ptr<NetDevice> oif (0); //specify non-zero if bound to a source address
-      route = ipv4->GetRoutingProtocol ()->RouteOutput (packet, header, oif, errno_);
+      if (ipv4->GetRoutingProtocol () != 0)
+        {
+          route = ipv4->GetRoutingProtocol ()->RouteOutput (packet, header, oif, errno_);
+        }
+      else
+        {
+          NS_LOG_ERROR ("No IPV4 Routing Protocol");
+          route = 0;
+        }
       ipv4->Send (packet, saddr, daddr, PROT_NUMBER, route);
     }
 }
@@ -623,7 +631,15 @@
       header.SetProtocol (PROT_NUMBER);
       Socket::SocketErrno errno_;
       Ptr<Ipv4Route> route;
-      route = ipv4->GetRoutingProtocol ()->RouteOutput (packet, header, oif, errno_);
+      if (ipv4->GetRoutingProtocol () != 0)
+        {
+          route = ipv4->GetRoutingProtocol ()->RouteOutput (packet, header, oif, errno_);
+        }
+      else
+        {
+          NS_LOG_ERROR ("No IPV4 Routing Protocol");
+          route = 0;
+        }
       ipv4->Send (packet, saddr, daddr, PROT_NUMBER, route);
     }
   else

--- a/src/internet-stack/tcp-socket-impl.cc	Tue Feb 09 10:40:54 2010 +0100
+++ b/src/internet-stack/tcp-socket-impl.cc	Wed Feb 10 11:03:32 2010 +0100
@@ -358,6 +358,7 @@
   NS_LOG_FUNCTION (this << address);
 
   Ptr<Ipv4> ipv4 = m_node->GetObject<Ipv4> ();
+  NS_ASSERT (ipv4 != 0);
 
   if (m_endPoint == 0)
     {
@@ -772,11 +773,17 @@
   Ptr<Packet> p = Create<Packet> ();
   TcpHeader header;
 
+  if (m_endPoint == 0) 
+    {
+      NS_LOG_WARN ("Failed to send empty packet due to null endpoint");
+      return;
+    }
+
   if (flags & TcpHeader::FIN)
     {
       flags |= TcpHeader::ACK;
     }
-
+ 
   header.SetFlags (flags);
   header.SetSequenceNumber (m_nextTxSequence);
   header.SetAckNumber (m_nextRxSequence);
@@ -811,9 +818,12 @@
   SendEmptyPacket(TcpHeader::RST);
   NotifyErrorClose();
   CancelAllTimers();
-  m_endPoint->SetDestroyCallback(MakeNullCallback<void>());
-  m_tcp->DeAllocate (m_endPoint);
-  m_endPoint = 0;
+  if (m_endPoint != 0) 
+    {
+      m_endPoint->SetDestroyCallback(MakeNullCallback<void>());
+      m_tcp->DeAllocate (m_endPoint);
+      m_endPoint = 0;
+    }
 }
 
   
@@ -1093,6 +1103,11 @@
     {
       return false; // No data exists
     }
+  if (m_endPoint == 0)
+    {
+      NS_LOG_INFO ("TcpSocketImpl::SendPendingData: No endpoint; m_shutdownSend=" << m_shutdownSend);
+      return false; // Is this the right way to handle this condition?
+    }
   uint32_t nPacketsSent = 0;
   while (m_pendingData->SizeFromSeq (m_firstPendingSequence, m_nextTxSequence))
     {
@@ -1142,7 +1157,7 @@
       if (m_shutdownSend)
         {
           m_errno = ERROR_SHUTDOWN;
-          return -1;
+          return false;
         }