diff --git a/src/core/thread/mesh_forwarder.cpp b/src/core/thread/mesh_forwarder.cpp
index b38aa06a7..f10e47bd3 100644
--- a/src/core/thread/mesh_forwarder.cpp
+++ b/src/core/thread/mesh_forwarder.cpp
@@ -1065,7 +1065,7 @@ exit:
     }
 }
 
-void MeshForwarder::HandleFragment(uint8_t *               aFrame,
+void MeshForwarder::HandleFragment(const uint8_t *         aFrame,
                                    uint16_t                aFrameLength,
                                    const Mac::Address &    aMacSource,
                                    const Mac::Address &    aMacDest,
@@ -1083,14 +1083,17 @@ void MeshForwarder::HandleFragment(uint8_t *               aFrame,
 
     if (fragmentHeader.GetDatagramOffset() == 0)
     {
-        uint8_t priority;
-        int     headerLength;
+        uint16_t datagramSize = fragmentHeader.GetDatagramSize();
 
-        SuccessOrExit(error = GetFramePriority(aFrame, aFrameLength, aMacSource, aMacDest, priority));
+        error = FrameToMessage(aFrame, aFrameLength, datagramSize, aMacSource, aMacDest, message);
+        SuccessOrExit(error);
 
-        message = Get<MessagePool>().New(Message::kTypeIp6, 0, priority);
-        VerifyOrExit(message != NULL, error = OT_ERROR_NO_BUFS);
+        VerifyOrExit(datagramSize >= message->GetLength(), error = OT_ERROR_PARSE);
+        error = message->SetLength(datagramSize);
+        SuccessOrExit(error);
 
+        message->SetDatagramTag(fragmentHeader.GetDatagramTag());
+        message->SetTimeout(kReassemblyTimeout);
         message->SetLinkSecurityEnabled(aLinkInfo.mLinkSecurity);
         message->SetPanId(aLinkInfo.mPanId);
         message->AddRss(aLinkInfo.mRss);
@@ -1098,21 +1101,6 @@ void MeshForwarder::HandleFragment(uint8_t *               aFrame,
         message->SetTimeSyncSeq(aLinkInfo.mTimeSyncSeq);
         message->SetNetworkTimeOffset(aLinkInfo.mNetworkTimeOffset);
 #endif
-        headerLength = Get<Lowpan::Lowpan>().Decompress(*message, aMacSource, aMacDest, aFrame, aFrameLength,
-                                                        fragmentHeader.GetDatagramSize());
-        VerifyOrExit(headerLength > 0, error = OT_ERROR_PARSE);
-
-        aFrame += headerLength;
-        aFrameLength -= static_cast<uint16_t>(headerLength);
-
-        VerifyOrExit(fragmentHeader.GetDatagramSize() >= message->GetOffset() + aFrameLength, error = OT_ERROR_PARSE);
-
-        SuccessOrExit(error = message->SetLength(fragmentHeader.GetDatagramSize()));
-
-        message->SetDatagramTag(fragmentHeader.GetDatagramTag());
-        message->SetTimeout(kReassemblyTimeout);
-        message->Write(message->GetOffset(), aFrameLength, aFrame);
-        message->MoveOffset(aFrameLength);
 
         // Security Check
         VerifyOrExit(Get<Ip6::Filter>().Accept(*message), error = OT_ERROR_DROP);
@@ -1257,7 +1245,39 @@ bool MeshForwarder::UpdateReassemblyList(void)
     return mReassemblyList.GetHead() != NULL;
 }
 
-void MeshForwarder::HandleLowpanHC(uint8_t *               aFrame,
+otError MeshForwarder::FrameToMessage(const uint8_t *     aFrame,
+                                      uint16_t            aFrameLength,
+                                      uint16_t            aDatagramSize,
+                                      const Mac::Address &aMacSource,
+                                      const Mac::Address &aMacDest,
+                                      Message *&          aMessage)
+{
+    otError error = OT_ERROR_NONE;
+    int     headerLength;
+    uint8_t priority;
+
+    error = GetFramePriority(aFrame, aFrameLength, aMacSource, aMacDest, priority);
+    SuccessOrExit(error);
+
+    aMessage = Get<MessagePool>().New(Message::kTypeIp6, 0, priority);
+    VerifyOrExit(aMessage, error = OT_ERROR_NO_BUFS);
+
+    headerLength =
+        Get<Lowpan::Lowpan>().Decompress(*aMessage, aMacSource, aMacDest, aFrame, aFrameLength, aDatagramSize);
+    VerifyOrExit(headerLength > 0, error = OT_ERROR_PARSE);
+
+    aFrame += headerLength;
+    aFrameLength -= static_cast<uint16_t>(headerLength);
+
+    SuccessOrExit(error = aMessage->SetLength(aMessage->GetLength() + aFrameLength));
+    aMessage->Write(aMessage->GetOffset(), aFrameLength, aFrame);
+    aMessage->MoveOffset(aFrameLength);
+
+exit:
+    return error;
+}
+
+void MeshForwarder::HandleLowpanHC(const uint8_t *         aFrame,
                                    uint16_t                aFrameLength,
                                    const Mac::Address &    aMacSource,
                                    const Mac::Address &    aMacDest,
@@ -1265,15 +1285,14 @@ void MeshForwarder::HandleLowpanHC(uint8_t *               aFrame,
 {
     otError  error   = OT_ERROR_NONE;
     Message *message = NULL;
-    int      headerLength;
-    uint8_t  priority;
 
 #if OPENTHREAD_FTD
     UpdateRoutes(aFrame, aFrameLength, aMacSource, aMacDest);
 #endif
 
-    SuccessOrExit(error = GetFramePriority(aFrame, aFrameLength, aMacSource, aMacDest, priority));
-    VerifyOrExit((message = Get<MessagePool>().New(Message::kTypeIp6, 0, priority)) != NULL, error = OT_ERROR_NO_BUFS);
+    error = FrameToMessage(aFrame, aFrameLength, 0, aMacSource, aMacDest, message);
+    SuccessOrExit(error);
+
     message->SetLinkSecurityEnabled(aLinkInfo.mLinkSecurity);
     message->SetPanId(aLinkInfo.mPanId);
     message->AddRss(aLinkInfo.mRss);
@@ -1282,15 +1301,6 @@ void MeshForwarder::HandleLowpanHC(uint8_t *               aFrame,
     message->SetNetworkTimeOffset(aLinkInfo.mNetworkTimeOffset);
 #endif
 
-    headerLength = Get<Lowpan::Lowpan>().Decompress(*message, aMacSource, aMacDest, aFrame, aFrameLength, 0);
-    VerifyOrExit(headerLength > 0, error = OT_ERROR_PARSE);
-
-    aFrame += headerLength;
-    aFrameLength -= static_cast<uint16_t>(headerLength);
-
-    SuccessOrExit(error = message->SetLength(message->GetLength() + aFrameLength));
-    message->Write(message->GetOffset(), aFrameLength, aFrame);
-
     // Security Check
     VerifyOrExit(Get<Ip6::Filter>().Accept(*message), error = OT_ERROR_DROP);
 
diff --git a/src/core/thread/mesh_forwarder.hpp b/src/core/thread/mesh_forwarder.hpp
index 7321a4478..7a8334d6b 100644
--- a/src/core/thread/mesh_forwarder.hpp
+++ b/src/core/thread/mesh_forwarder.hpp
@@ -340,7 +340,7 @@ private:
                               uint16_t            aFrameLength,
                               const Mac::Address &aMeshSource,
                               const Mac::Address &aMeshDest);
-    void    UpdateRoutes(uint8_t *           aFrame,
+    void    UpdateRoutes(const uint8_t *     aFrame,
                          uint16_t            aFrameLength,
                          const Mac::Address &aMeshSource,
                          const Mac::Address &aMeshDest);
@@ -352,6 +352,12 @@ private:
                                  Ip6::Header &       aIp6Header,
                                  uint8_t &           aHeaderLength,
                                  bool &              aNextHeaderCompressed);
+    otError  FrameToMessage(const uint8_t *     aFrame,
+                            uint16_t            aFrameLength,
+                            uint16_t            aDatagramSize,
+                            const Mac::Address &aMacSource,
+                            const Mac::Address &aMacDest,
+                            Message *&          aMessage);
     otError  GetIp6Header(const uint8_t *     aFrame,
                           uint16_t            aFrameLength,
                           const Mac::Address &aMacSource,
@@ -365,12 +371,12 @@ private:
                         uint16_t                aFrameLength,
                         const Mac::Address &    aMacSource,
                         const otThreadLinkInfo &aLinkInfo);
-    void     HandleFragment(uint8_t *               aFrame,
+    void     HandleFragment(const uint8_t *         aFrame,
                             uint16_t                aFrameLength,
                             const Mac::Address &    aMacSource,
                             const Mac::Address &    aMacDest,
                             const otThreadLinkInfo &aLinkInfo);
-    void     HandleLowpanHC(uint8_t *               aFrame,
+    void     HandleLowpanHC(const uint8_t *         aFrame,
                             uint16_t                aFrameLength,
                             const Mac::Address &    aMacSource,
                             const Mac::Address &    aMacDest,
diff --git a/src/core/thread/mesh_forwarder_ftd.cpp b/src/core/thread/mesh_forwarder_ftd.cpp
index 1160f2f56..048f1f7a9 100644
--- a/src/core/thread/mesh_forwarder_ftd.cpp
+++ b/src/core/thread/mesh_forwarder_ftd.cpp
@@ -634,7 +634,7 @@ exit:
     }
 }
 
-void MeshForwarder::UpdateRoutes(uint8_t *           aFrame,
+void MeshForwarder::UpdateRoutes(const uint8_t *     aFrame,
                                  uint16_t            aFrameLength,
                                  const Mac::Address &aMeshSource,
                                  const Mac::Address &aMeshDest)