EthernetFragmentFcs*: Fixed issue #1020, fix provided by HannHank.

The mCRC has to be calculated cumulatively including all bytes up to the current fragment.
See the issue for more details.

Author: levy

src/inet/linklayer/ethernet/modular/EthernetFragmentFcsChecker.cc

@@ -20,11 +20,9 @@ bool EthernetFragmentFcsChecker::checkComputedChecksum(const Packet *packet, Che
 {
     auto data = packet->peekDataAsBytes();
     auto bytes = data->getBytes();
-    uint64_t fragmentFcs = ethernetFcs(bytes.data(), packet->getByteLength() - 4);
     auto& fragmentTag = packet->getTag<FragmentTag>();
     currentFragmentCompleteFcs = ethernetFcs(bytes.data(), packet->getByteLength() - 4, fragmentTag->getFirstFragment() ? 0 : lastFragmentCompleteFcs);
-    bool lastFragment = receivedFcs != (fragmentFcs ^ 0xFFFF0000);
-    return !lastFragment || receivedFcs == currentFragmentCompleteFcs;
+    return receivedFcs == currentFragmentCompleteFcs || receivedFcs == (currentFragmentCompleteFcs ^ 0xFFFF0000);
 }
 
 void EthernetFragmentFcsChecker::processPacket(Packet *packet)

src/inet/linklayer/ethernet/modular/EthernetFragmentFcsInserter.cc

@@ -25,7 +25,7 @@ uint64_t EthernetFragmentFcsInserter::computeComputedChecksum(const Packet *pack
     if (fragmentTag->getLastFragment())
         return currentFragmentCompleteFcs;
     else
-        return ethernetFcs(bytes.data(), bytes.size()) ^ 0xFFFF0000;
+        return currentFragmentCompleteFcs ^ 0xFFFF0000;
 }
 
 void EthernetFragmentFcsInserter::processPacket(Packet *packet)