From 42825825352cbc2f01a8b59a8c254ff94fd267b8 Mon Sep 17 00:00:00 2001
From: Tom Goff <tgoff@tgoff.net>
Date: Thu, 12 May 2011 21:19:07 -0700
Subject: [PATCH] bug 1056: CSMA: padding not handled correctly for LLC
 encapsulation

---
 RELEASE_NOTES                     |  1 +
 src/csma/model/csma-net-device.cc | 22 ++++++++++++++++------
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/RELEASE_NOTES b/RELEASE_NOTES
index 12e3e0ce6..f574a7635 100644
--- a/RELEASE_NOTES
+++ b/RELEASE_NOTES
@@ -72,6 +72,7 @@ since ns-3.10, in many cases referencing the Bugzilla bug number.
    - bug 1038 - Time::Get*Seconds () return signed integer while actually returning unsigned
    - bug 445 - Is the class name Scalar in nstime.h appropriate?
    - bug 1044 - Seconds (1e-9) creates Time that is not IsPositive ()
+   - bug 1056 - CSMA: padding not handled correctly for LLC encapsulation
 
 Known issues
 ------------
diff --git a/src/csma/model/csma-net-device.cc b/src/csma/model/csma-net-device.cc
index f5d018ef8..dd55fdc0f 100644
--- a/src/csma/model/csma-net-device.cc
+++ b/src/csma/model/csma-net-device.cc
@@ -321,6 +321,13 @@ CsmaNetDevice::AddHeader (Ptr<Packet> p,   Mac48Address source,  Mac48Address de
         llc.SetType (protocolNumber);
         p->AddHeader (llc);
 
+        //
+        // This corresponds to the length interpretation of the lengthType 
+        // field but with an LLC/SNAP header added to the payload as in 
+        // IEEE 802.2
+        //
+        lengthType = p->GetSize ();
+
         //
         // All Ethernet frames must carry a minimum payload of 46 bytes.  The 
         // LLC SNAP header counts as part of this payload.  We need to padd out
@@ -335,12 +342,7 @@ CsmaNetDevice::AddHeader (Ptr<Packet> p,   Mac48Address source,  Mac48Address de
             p->AddAtEnd (padd);
           }
 
-        //
-        // This corresponds to the length interpretation of the lengthType field,
-        // but with an LLC/SNAP header added to the payload as in IEEE 802.2
-        //      
-        lengthType = p->GetSize ();
-        NS_ASSERT_MSG (lengthType <= GetMtu (),
+        NS_ASSERT_MSG (p->GetSize () <= GetMtu (),
           "CsmaNetDevice::AddHeader(): 802.3 Length/Type field with LLC/SNAP: "
           "length interpretation must not exceed device frame size minus overhead");
       }
@@ -721,6 +723,14 @@ CsmaNetDevice::Receive (Ptr<Packet> packet, Ptr<CsmaNetDevice> senderDevice)
   //
   if (header.GetLengthType () <= 1500)
     {
+      NS_ASSERT (packet->GetSize () >= header.GetLengthType ());
+      uint32_t padlen = packet->GetSize () - header.GetLengthType ();
+      NS_ASSERT (padlen <= 46);
+      if (padlen > 0)
+        {
+          packet->RemoveAtEnd (padlen);
+        }
+
       LlcSnapHeader llc;
       packet->RemoveHeader (llc);
       protocol = llc.GetType ();