Implement 2-hop loop avoidance. (#1091)

src/core/thread/mesh_forwarder.cpp

@@ -1487,7 +1487,7 @@ void MeshForwarder::HandleReceivedFrame(Mac::Frame &aFrame)
         if (payloadLength >= sizeof(Lowpan::MeshHeader) &&
             reinterpret_cast<Lowpan::MeshHeader *>(payload)->IsMeshHeader())
         {
-            HandleMesh(payload, payloadLength, messageInfo);
+            HandleMesh(payload, payloadLength, macSource, messageInfo);
         }
         else if (payloadLength >= sizeof(Lowpan::FragmentHeader) &&
                  reinterpret_cast<Lowpan::FragmentHeader *>(payload)->IsFragmentHeader())
@@ -1521,7 +1521,8 @@ exit:
     }
 }
 
-void MeshForwarder::HandleMesh(uint8_t *aFrame, uint8_t aFrameLength, const ThreadMessageInfo &aMessageInfo)
+void MeshForwarder::HandleMesh(uint8_t *aFrame, uint8_t aFrameLength, const Mac::Address &aMacSource,
+                               const ThreadMessageInfo &aMessageInfo)
 {
     ThreadError error = kThreadError_None;
     Message *message = NULL;
@@ -1560,6 +1561,8 @@ void MeshForwarder::HandleMesh(uint8_t *aFrame, uint8_t aFrameLength, const Thre
     }
     else if (meshHeader.GetHopsLeft() > 0)
     {
+        mMle.ResolveRoutingLoops(aMacSource.mShortAddress, meshDest.mShortAddress);
+
         SuccessOrExit(error = CheckReachability(aFrame, aFrameLength, meshSource, meshDest));
 
         meshHeader.SetHopsLeft(meshHeader.GetHopsLeft() - 1);

src/core/thread/mesh_forwarder.hpp

@@ -225,7 +225,8 @@ private:
     ThreadError GetMacSourceAddress(const Ip6::Address &aIp6Addr, Mac::Address &aMacAddr);
     Message *GetDirectTransmission(void);
     Message *GetIndirectTransmission(const Child &aChild);
-    void HandleMesh(uint8_t *aFrame, uint8_t aPayloadLength, const ThreadMessageInfo &aMessageInfo);
+    void HandleMesh(uint8_t *aFrame, uint8_t aPayloadLength, const Mac::Address &aMacSource,
+                    const ThreadMessageInfo &aMessageInfo);
     void HandleFragment(uint8_t *aFrame, uint8_t aPayloadLength,
                         const Mac::Address &aMacSource, const Mac::Address &aMacDest,
                         const ThreadMessageInfo &aMessageInfo);

src/core/thread/mle_router.cpp

@@ -3530,6 +3530,20 @@ exit:
     return error;
 }
 
+void MleRouter::ResolveRoutingLoops(uint16_t aSourceMac, uint16_t aDestRloc16)
+{
+    if (aSourceMac == GetNextHop(aDestRloc16))
+    {
+        // loop detected
+        Router *router = GetRouter(GetRouterId(aDestRloc16));
+        assert(router != NULL);
+
+        // invalidate next hop
+        router->mNextHop = kInvalidRouterId;
+        ResetAdvertiseInterval();
+    }
+}
+
 ThreadError MleRouter::CheckReachability(uint16_t aMeshSource, uint16_t aMeshDest, Ip6::Header &aIp6Header)
 {
     Ip6::Address destination;

src/core/thread/mle_router_ftd.hpp

@@ -665,6 +665,15 @@ public:
      */
     ThreadError CheckReachability(uint16_t aMeshSource, uint16_t aMeshDest, Ip6::Header &aIp6Header);
 
+    /**
+     * This method resolves 2-hop routing loops.
+     *
+     * @param[in]  aSourceMac   The RLOC16 of the previous hop.
+     * @param[in]  aDestRloc16  The RLOC16 of the final destination.
+     *
+     */
+    void ResolveRoutingLoops(uint16_t aSourceMac, uint16_t aDestRloc16);
+
     /**
      * This method checks if a given Router ID has correct value.
      *

src/core/thread/mle_router_mtd.hpp

@@ -135,6 +135,8 @@ public:
 
     static int ComparePartitions(bool, const LeaderDataTlv &, bool, const LeaderDataTlv &) { return 0; }
 
+    void ResolveRoutingLoops(uint16_t, uint16_t) { }
+
     ThreadError CheckReachability(uint16_t aMeshSource, uint16_t aMeshDest, Ip6::Header &aIp6Header) {
         return Mle::CheckReachability(aMeshSource, aMeshDest, aIp6Header);
     }