diff --git a/src/internet/model/icmpv4-l4-protocol.cc b/src/internet/model/icmpv4-l4-protocol.cc
index deee55424..0ea2b6955 100644
--- a/src/internet/model/icmpv4-l4-protocol.cc
+++ b/src/internet/model/icmpv4-l4-protocol.cc
@@ -57,7 +57,7 @@ Icmpv4L4Protocol::NotifyNewAggregate ()
       if (node != 0)
         {
           Ptr<Ipv4L3Protocol> ipv4 = this->GetObject<Ipv4L3Protocol> ();
-          if (ipv4 != 0)
+          if (ipv4 != 0 && m_downTarget.IsNull ())
             {
               this->SetNode (node);
               ipv4->Insert (this);
diff --git a/src/internet/model/icmpv6-l4-protocol.cc b/src/internet/model/icmpv6-l4-protocol.cc
index 14454f28f..fca45f34e 100644
--- a/src/internet/model/icmpv6-l4-protocol.cc
+++ b/src/internet/model/icmpv6-l4-protocol.cc
@@ -112,7 +112,7 @@ void Icmpv6L4Protocol::NotifyNewAggregate ()
       if (node != 0)
         {
           Ptr<Ipv6L3Protocol> ipv6 = this->GetObject<Ipv6L3Protocol> ();
-          if (ipv6 != 0)
+          if (ipv6 != 0 && m_downTarget.IsNull ())
             {
               SetNode (node);
               ipv6->Insert (this);
diff --git a/src/internet/model/nsc-tcp-l4-protocol.cc b/src/internet/model/nsc-tcp-l4-protocol.cc
index f14f8ef3d..d8ccfa94e 100644
--- a/src/internet/model/nsc-tcp-l4-protocol.cc
+++ b/src/internet/model/nsc-tcp-l4-protocol.cc
@@ -196,7 +196,7 @@ NscTcpL4Protocol::NotifyNewAggregate ()
       if (node != 0)
         {
           Ptr<Ipv4L3Protocol> ipv4 = this->GetObject<Ipv4L3Protocol> ();
-          if (ipv4 != 0)
+          if (ipv4 != 0 && m_downTarget.IsNull ())
             {
               this->SetNode (node);
               ipv4->Insert (this);
diff --git a/src/internet/model/tcp-l4-protocol.cc b/src/internet/model/tcp-l4-protocol.cc
index 00d865f6e..ba861e55f 100644
--- a/src/internet/model/tcp-l4-protocol.cc
+++ b/src/internet/model/tcp-l4-protocol.cc
@@ -132,12 +132,12 @@ TcpL4Protocol::NotifyNewAggregate ()
   // need to keep track of whether we are connected to an IPv4 or
   // IPv6 lower layer and call the appropriate one.
   
-  if (ipv4 != 0)
+  if (ipv4 != 0 && m_downTarget.IsNull ())
     {
       ipv4->Insert(this);
       this->SetDownTarget(MakeCallback(&Ipv4::Send, ipv4));
     }
-  if (ipv6 != 0)
+  if (ipv6 != 0 && m_downTarget6.IsNull ())
     {
       ipv6->Insert(this);
       this->SetDownTarget6(MakeCallback(&Ipv6L3Protocol::Send, ipv6));
diff --git a/src/internet/model/udp-l4-protocol.cc b/src/internet/model/udp-l4-protocol.cc
index dedda074a..83034e44b 100644
--- a/src/internet/model/udp-l4-protocol.cc
+++ b/src/internet/model/udp-l4-protocol.cc
@@ -88,6 +88,7 @@ UdpL4Protocol::SetNode (Ptr<Node> node)
 void
 UdpL4Protocol::NotifyNewAggregate ()
 {
+  NS_LOG_FUNCTION (this);
   Ptr<Node> node = this->GetObject<Node> ();
   Ptr<Ipv4> ipv4 = this->GetObject<Ipv4> ();
   Ptr<Ipv6L3Protocol> ipv6 = node->GetObject<Ipv6L3Protocol> ();
@@ -108,12 +109,12 @@ UdpL4Protocol::NotifyNewAggregate ()
   // need to keep track of whether we are connected to an IPv4 or
   // IPv6 lower layer and call the appropriate one.
   
-  if (ipv4 != 0)
+  if (ipv4 != 0 && m_downTarget.IsNull())
     {
       ipv4->Insert (this);
       this->SetDownTarget (MakeCallback (&Ipv4::Send, ipv4));
     }
-  if (ipv6 != 0)
+  if (ipv6 != 0 && m_downTarget6.IsNull())
     {
       ipv6->Insert (this);
       this->SetDownTarget6 (MakeCallback (&Ipv6L3Protocol::Send, ipv6));
@@ -499,6 +500,7 @@ UdpL4Protocol::Send (Ptr<Packet> packet,
 void
 UdpL4Protocol::SetDownTarget (IpL4Protocol::DownTargetCallback callback)
 {
+  NS_LOG_FUNCTION (this);
   m_downTarget = callback;
 }
 
@@ -511,6 +513,7 @@ UdpL4Protocol::GetDownTarget (void) const
 void
 UdpL4Protocol::SetDownTarget6 (IpL4Protocol::DownTargetCallback6 callback)
 {
+  NS_LOG_FUNCTION (this);
   m_downTarget6 = callback;
 }