[dua] fix Parent failed to send reregister for MTD Child on receiving ST_DUA_REREGISTER (#6637)

This commit enhances DUA response handling for ST_DUA_REREGISTER:
- Parent will stop registering DUA for MTD Child until the next Child
  Update Request.
- MTD Child will re-register its DUA by Child Update Request or
  DUA.req.

src/core/thread/dua_manager.cpp

@@ -61,7 +61,6 @@ DuaManager::DuaManager(Instance &aInstance)
 #endif
 #if OPENTHREAD_FTD && OPENTHREAD_CONFIG_TMF_PROXY_DUA_ENABLE
     , mChildIndexDuaRegistering(0)
-    , mRegisterCurrentChildIndex(false)
 #endif
 {
     mDelay.mValue = 0;
@@ -98,7 +97,6 @@ void DuaManager::HandleDomainPrefixUpdate(BackboneRouter::Leader::DomainPrefixSt
         {
             mChildDuaMask.Clear();
             mChildDuaRegisteredMask.Clear();
-            mRegisterCurrentChildIndex = false;
         }
 #endif
     }
@@ -476,7 +474,7 @@ void DuaManager::PerformNextRegistration(void)
         const Ip6::Address *duaPtr = nullptr;
         Child *             child  = nullptr;
 
-        if (!mRegisterCurrentChildIndex)
+        if (!mChildDuaMask.Get(mChildIndexDuaRegistering))
         {
             for (Child &iter : Get<ChildTable>().Iterate(Child::kInStateValid))
             {
@@ -623,8 +621,11 @@ Error DuaManager::ProcessDuaResponse(Coap::Message &aMessage)
             mDuaState             = kRegistered;
             break;
         case ThreadStatusTlv::kDuaReRegister:
-            mDuaState                  = kToRegister;
-            mDelay.mFields.mCheckDelay = Mle::kImmediateReRegisterDelay;
+            if (Get<ThreadNetif>().HasUnicastAddress(GetDomainUnicastAddress()))
+            {
+                RemoveDomainUnicastAddress();
+                AddDomainUnicastAddress();
+            }
             break;
         case ThreadStatusTlv::kDuaInvalid:
             // Domain Prefix might be invalid.
@@ -649,8 +650,6 @@ Error DuaManager::ProcessDuaResponse(Coap::Message &aMessage)
         VerifyOrExit(child != nullptr, error = kErrorNotFound);
         VerifyOrExit(child->HasIp6Address(target), error = kErrorNotFound);
 
-        mRegisterCurrentChildIndex = false;
-
         switch (status)
         {
         case ThreadStatusTlv::kDuaSuccess:
@@ -658,8 +657,9 @@ Error DuaManager::ProcessDuaResponse(Coap::Message &aMessage)
             mChildDuaRegisteredMask.Set(mChildIndexDuaRegistering, true);
             break;
         case ThreadStatusTlv::kDuaReRegister:
-            mRegisterCurrentChildIndex = true;
-            mDelay.mFields.mCheckDelay = Mle::kImmediateReRegisterDelay;
+            // Parent stops registering for the Child's DUA until next Child Update Request
+            mChildDuaMask.Set(mChildIndexDuaRegistering, false);
+            mChildDuaRegisteredMask.Set(mChildIndexDuaRegistering, false);
             break;
         case ThreadStatusTlv::kDuaInvalid:
         case ThreadStatusTlv::kDuaDuplicate:
@@ -738,16 +738,14 @@ void DuaManager::UpdateChildDomainUnicastAddress(const Child &aChild, Mle::Child
 #endif
         {
             IgnoreError(Get<Tmf::Agent>().AbortTransaction(&DuaManager::HandleDuaResponse, this));
-
-            // Reset mRegisterCurrentChildIndex properly
-            mRegisterCurrentChildIndex = mRegisterCurrentChildIndex && (aState == Mle::ChildDuaState::kRemoved);
         }
 
         mChildDuaMask.Set(childIndex, false);
         mChildDuaRegisteredMask.Set(childIndex, false);
     }
 
-    if (aState == Mle::ChildDuaState::kAdded || aState == Mle::ChildDuaState::kChanged)
+    if (aState == Mle::ChildDuaState::kAdded || aState == Mle::ChildDuaState::kChanged ||
+        (aState == Mle::ChildDuaState::kUnchanged && !mChildDuaMask.Get(childIndex)))
     {
         if (mChildDuaMask == mChildDuaRegisteredMask)
         {

src/core/thread/dua_manager.hpp

@@ -257,10 +257,9 @@ private:
     // TODO: (DUA) may re-evaluate the alternative option of distributing the flags into the child table:
     //       - Child class itself have some padding - may save some RAM
     //       - Avoid cross reference between a bit-vector and the child entry
-    ChildMask mChildDuaMask;           ///< Child Mask for child who registers DUA via Child Update Request.
-    ChildMask mChildDuaRegisteredMask; ///< Child Mask for child's DUA that was registered by the parent on behalf.
-    uint16_t  mChildIndexDuaRegistering : 15; ///< Child Index of the DUA being registered.
-    bool      mRegisterCurrentChildIndex : 1; ///< Re-register the child just registered.
+    ChildMask mChildDuaMask;             ///< Child Mask for child who registers DUA via Child Update Request.
+    ChildMask mChildDuaRegisteredMask;   ///< Child Mask for child's DUA that was registered by the parent on behalf.
+    uint16_t  mChildIndexDuaRegistering; ///< Child Index of the DUA being registered.
 #endif
 };
 

src/core/thread/mle_router.cpp

@@ -2052,10 +2052,8 @@ Error MleRouter::UpdateChildAddresses(const Message &aMessage, uint16_t aOffset,
 
                 if (oldDuaPtr != nullptr)
                 {
-                    if (oldDua != address)
-                    {
-                        Get<DuaManager>().UpdateChildDomainUnicastAddress(aChild, ChildDuaState::kChanged);
-                    }
+                    Get<DuaManager>().UpdateChildDomainUnicastAddress(
+                        aChild, oldDua != address ? ChildDuaState::kChanged : ChildDuaState::kUnchanged);
                 }
                 else
                 {

src/core/thread/mle_types.hpp

@@ -296,9 +296,10 @@ static_assert(kTimeSinceLastTransactionMax * 1000 > kTimeSinceLastTransactionMax
  */
 enum class ChildDuaState : uint8_t
 {
-    kAdded,   ///< A new DUA registered by the Child via Address Registration.
-    kChanged, ///< A different DUA registered by the Child via Address Registration.
-    kRemoved, ///< DUA registered by the Child is removed and not in Address Registration.
+    kAdded,     ///< A new DUA registered by the Child via Address Registration.
+    kChanged,   ///< A different DUA registered by the Child via Address Registration.
+    kRemoved,   ///< DUA registered by the Child is removed and not in Address Registration.
+    kUnchanged, ///< The Child registers the same DUA again.
 };
 
 #endif // OPENTHREAD_CONFIG_THREAD_VERSION >= OT_THREAD_VERSION_1_2