diff --git a/src/core/api/commissioner_api.cpp b/src/core/api/commissioner_api.cpp
index 1e10f677d..8c549098a 100644
--- a/src/core/api/commissioner_api.cpp
+++ b/src/core/api/commissioner_api.cpp
@@ -117,8 +117,8 @@ otError otCommissionerAnnounceBegin(otInstance *aInstance, uint32_t aChannelMask
     otError error = OT_ERROR_DISABLED_FEATURE;
 
 #if OPENTHREAD_FTD && OPENTHREAD_ENABLE_COMMISSIONER
-    error = aInstance->mThreadNetif.GetCommissioner().mAnnounceBegin.SendRequest(aChannelMask, aCount, aPeriod,
-                                                                                 *static_cast<const Ip6::Address *>(aAddress));
+    error = aInstance->mThreadNetif.GetCommissioner().GetAnnounceBeginClient().SendRequest(
+                aChannelMask, aCount, aPeriod, *static_cast<const Ip6::Address *>(aAddress));
 #else  // OPENTHREAD_ENABLE_COMMISSIONER && OPENTHREAD_FTD
     OT_UNUSED_VARIABLE(aInstance);
     OT_UNUSED_VARIABLE(aChannelMask);
@@ -137,9 +137,9 @@ otError otCommissionerEnergyScan(otInstance *aInstance, uint32_t aChannelMask, u
     otError error = OT_ERROR_DISABLED_FEATURE;
 
 #if OPENTHREAD_FTD && OPENTHREAD_ENABLE_COMMISSIONER
-    error = aInstance->mThreadNetif.GetCommissioner().mEnergyScan.SendQuery(aChannelMask, aCount, aPeriod, aScanDuration,
-                                                                            *static_cast<const Ip6::Address *>(aAddress),
-                                                                            aCallback, aContext);
+    error = aInstance->mThreadNetif.GetCommissioner().GetEnergyScanClient().SendQuery(
+                aChannelMask, aCount, aPeriod, aScanDuration, *static_cast<const Ip6::Address *>(aAddress),
+                aCallback, aContext);
 #else  // OPENTHREAD_ENABLE_COMMISSIONER && OPENTHREAD_FTD
     OT_UNUSED_VARIABLE(aInstance);
     OT_UNUSED_VARIABLE(aChannelMask);
@@ -161,7 +161,7 @@ otError otCommissionerPanIdQuery(otInstance *aInstance, uint16_t aPanId, uint32_
     otError error = OT_ERROR_DISABLED_FEATURE;
 
 #if OPENTHREAD_FTD && OPENTHREAD_ENABLE_COMMISSIONER
-    error = aInstance->mThreadNetif.GetCommissioner().mPanIdQuery.SendQuery(
+    error = aInstance->mThreadNetif.GetCommissioner().GetPanIdQueryClient().SendQuery(
                 aPanId, aChannelMask, *static_cast<const Ip6::Address *>(aAddress), aCallback, aContext);
 #else  // OPENTHREAD_ENABLE_COMMISSIONER && OPENTHREAD_FTD
     OT_UNUSED_VARIABLE(aInstance);
diff --git a/src/core/api/icmp6_api.cpp b/src/core/api/icmp6_api.cpp
index dfc77f9d0..7d5aed4f7 100644
--- a/src/core/api/icmp6_api.cpp
+++ b/src/core/api/icmp6_api.cpp
@@ -41,23 +41,23 @@ using namespace ot;
 
 bool otIcmp6IsEchoEnabled(otInstance *aInstance)
 {
-    return aInstance->mIp6.mIcmp.IsEchoEnabled();
+    return aInstance->mIp6.GetIcmp().IsEchoEnabled();
 }
 
 void otIcmp6SetEchoEnabled(otInstance *aInstance, bool aEnabled)
 {
-    aInstance->mIp6.mIcmp.SetEchoEnabled(aEnabled);
+    aInstance->mIp6.GetIcmp().SetEchoEnabled(aEnabled);
 }
 
 otError otIcmp6RegisterHandler(otInstance *aInstance, otIcmp6Handler *aHandler)
 {
-    return aInstance->mIp6.mIcmp.RegisterHandler(*static_cast<Ip6::IcmpHandler *>(aHandler));
+    return aInstance->mIp6.GetIcmp().RegisterHandler(*static_cast<Ip6::IcmpHandler *>(aHandler));
 }
 
 otError otIcmp6SendEchoRequest(otInstance *aInstance, otMessage *aMessage,
                                const otMessageInfo *aMessageInfo, uint16_t aIdentifier)
 {
-    return aInstance->mIp6.mIcmp.SendEchoRequest(*static_cast<Message *>(aMessage),
-                                                 *static_cast<const Ip6::MessageInfo *>(aMessageInfo),
-                                                 aIdentifier);
+    return aInstance->mIp6.GetIcmp().SendEchoRequest(*static_cast<Message *>(aMessage),
+                                                     *static_cast<const Ip6::MessageInfo *>(aMessageInfo),
+                                                     aIdentifier);
 }
diff --git a/src/core/api/message_api.cpp b/src/core/api/message_api.cpp
index afe269750..dda8d7ed0 100644
--- a/src/core/api/message_api.cpp
+++ b/src/core/api/message_api.cpp
@@ -178,8 +178,8 @@ void otMessageGetBufferInfo(otInstance *aInstance, otBufferInfo *aBufferInfo)
     aInstance->mThreadNetif.GetIp6().GetSendQueue().GetInfo(aBufferInfo->mIp6Messages,
                                                             aBufferInfo->mIp6Buffers);
 
-    aInstance->mThreadNetif.GetIp6().mMpl.GetBufferedMessageSet().GetInfo(aBufferInfo->mMplMessages,
-                                                                          aBufferInfo->mMplBuffers);
+    aInstance->mThreadNetif.GetIp6().GetMpl().GetBufferedMessageSet().GetInfo(aBufferInfo->mMplMessages,
+                                                                              aBufferInfo->mMplBuffers);
 
     aInstance->mThreadNetif.GetMle().GetMessageQueue().GetInfo(aBufferInfo->mMleMessages,
                                                                aBufferInfo->mMleBuffers);
diff --git a/src/core/api/udp_api.cpp b/src/core/api/udp_api.cpp
index 6431db854..90db4f37c 100644
--- a/src/core/api/udp_api.cpp
+++ b/src/core/api/udp_api.cpp
@@ -41,7 +41,7 @@ using namespace ot;
 
 otMessage *otUdpNewMessage(otInstance *aInstance, bool aLinkSecurityEnabled)
 {
-    Message *message = aInstance->mIp6.mUdp.NewMessage(0);
+    Message *message = aInstance->mIp6.GetUdp().NewMessage(0);
 
     if (message)
     {
@@ -58,7 +58,7 @@ otError otUdpOpen(otInstance *aInstance, otUdpSocket *aSocket, otUdpReceive aCal
 
     if (socket->mTransport == NULL)
     {
-        socket->mTransport = &aInstance->mIp6.mUdp;
+        socket->mTransport = &aInstance->mIp6.GetUdp();
         error = socket->Open(aCallback, aCallbackContext);
     }
 
diff --git a/src/core/coap/coap.cpp b/src/core/coap/coap.cpp
index 6e04532b5..9bd7e1d8c 100644
--- a/src/core/coap/coap.cpp
+++ b/src/core/coap/coap.cpp
@@ -51,7 +51,7 @@ namespace Coap {
 CoapBase::CoapBase(otInstance &aInstance, Timer::Handler aRetransmissionTimerHandler,
                    Timer::Handler aResponsesQueueTimerHandler):
     InstanceLocator(aInstance),
-    mSocket(aInstance.mThreadNetif.GetIp6().mUdp),
+    mSocket(aInstance.mThreadNetif.GetIp6().GetUdp()),
     mRetransmissionTimer(aInstance, aRetransmissionTimerHandler, this),
     mResources(NULL),
     mContext(NULL),
diff --git a/src/core/mac/mac.cpp b/src/core/mac/mac.cpp
index 715f4af8d..0bdfdd0e1 100644
--- a/src/core/mac/mac.cpp
+++ b/src/core/mac/mac.cpp
@@ -138,17 +138,6 @@ void Mac::StartCsmaBackoff(void)
 
 Mac::Mac(otInstance &aInstance):
     InstanceLocator(aInstance),
-    mMacTimer(aInstance, &Mac::HandleMacTimer, this),
-    mBackoffTimer(aInstance, &Mac::HandleBeginTransmit, this),
-    mReceiveTimer(aInstance, &Mac::HandleReceiveTimer, this),
-    mShortAddress(kShortAddrInvalid),
-    mPanId(kPanIdBroadcast),
-    mChannel(OPENTHREAD_CONFIG_DEFAULT_CHANNEL),
-    mMaxTransmitPower(OPENTHREAD_CONFIG_DEFAULT_MAX_TRANSMIT_POWER),
-    mSendHead(NULL),
-    mSendTail(NULL),
-    mReceiveHead(NULL),
-    mReceiveTail(NULL),
     mOperation(kOperationIdle),
     mPendingActiveScan(false),
     mPendingEnergyScan(false),
@@ -160,6 +149,17 @@ Mac::Mac(otInstance &aInstance):
 #if OPENTHREAD_CONFIG_STAY_AWAKE_BETWEEN_FRAGMENTS
     mDelaySleep(false),
 #endif
+    mMacTimer(aInstance, &Mac::HandleMacTimer, this),
+    mBackoffTimer(aInstance, &Mac::HandleBeginTransmit, this),
+    mReceiveTimer(aInstance, &Mac::HandleReceiveTimer, this),
+    mShortAddress(kShortAddrInvalid),
+    mPanId(kPanIdBroadcast),
+    mChannel(OPENTHREAD_CONFIG_DEFAULT_CHANNEL),
+    mMaxTransmitPower(OPENTHREAD_CONFIG_DEFAULT_MAX_TRANSMIT_POWER),
+    mSendHead(NULL),
+    mSendTail(NULL),
+    mReceiveHead(NULL),
+    mReceiveTail(NULL),
     mBeaconSequence(static_cast<uint8_t>(otPlatRandomGet())),
     mDataSequence(static_cast<uint8_t>(otPlatRandomGet())),
     mCsmaAttempts(0),
diff --git a/src/core/mac/mac.hpp b/src/core/mac/mac.hpp
index 7ee25b051..4263b5aa6 100644
--- a/src/core/mac/mac.hpp
+++ b/src/core/mac/mac.hpp
@@ -682,6 +682,19 @@ private:
 
     static const char *OperationToString(Operation aOperation);
 
+    Operation mOperation;
+
+    bool mPendingActiveScan       : 1;
+    bool mPendingEnergyScan       : 1;
+    bool mPendingTransmitBeacon   : 1;
+    bool mPendingTransmitData     : 1;
+    bool mPendingWaitingForData   : 1;
+    bool mRxOnWhenIdle            : 1;
+    bool mBeaconsEnabled          : 1;
+#if OPENTHREAD_CONFIG_STAY_AWAKE_BETWEEN_FRAGMENTS
+    bool mDelaySleep              : 1;
+#endif
+
     TimerMilli mMacTimer;
 #if OPENTHREAD_CONFIG_ENABLE_PLATFORM_USEC_TIMER
     TimerMicro mBackoffTimer;
@@ -702,19 +715,6 @@ private:
     Sender *mSendHead, *mSendTail;
     Receiver *mReceiveHead, *mReceiveTail;
 
-    Operation mOperation;
-
-    bool mPendingActiveScan       : 1;
-    bool mPendingEnergyScan       : 1;
-    bool mPendingTransmitBeacon   : 1;
-    bool mPendingTransmitData     : 1;
-    bool mPendingWaitingForData   : 1;
-    bool mRxOnWhenIdle            : 1;
-    bool mBeaconsEnabled          : 1;
-#if OPENTHREAD_CONFIG_STAY_AWAKE_BETWEEN_FRAGMENTS
-    bool mDelaySleep              : 1;
-#endif
-
     uint8_t mBeaconSequence;
     uint8_t mDataSequence;
     uint8_t mCsmaAttempts;
diff --git a/src/core/meshcop/commissioner.cpp b/src/core/meshcop/commissioner.cpp
index 026ef7fc8..5be94538c 100644
--- a/src/core/meshcop/commissioner.cpp
+++ b/src/core/meshcop/commissioner.cpp
@@ -62,9 +62,6 @@ namespace MeshCoP {
 
 Commissioner::Commissioner(otInstance &aInstance):
     InstanceLocator(aInstance),
-    mAnnounceBegin(aInstance),
-    mEnergyScan(aInstance),
-    mPanIdQuery(aInstance),
     mState(OT_COMMISSIONER_STATE_DISABLED),
     mJoinerPort(0),
     mJoinerRloc(0),
@@ -74,7 +71,10 @@ Commissioner::Commissioner(otInstance &aInstance):
     mTransmitAttempts(0),
     mRelayReceive(OT_URI_PATH_RELAY_RX, &Commissioner::HandleRelayReceive, this),
     mDatasetChanged(OT_URI_PATH_DATASET_CHANGED, &Commissioner::HandleDatasetChanged, this),
-    mJoinerFinalize(OT_URI_PATH_JOINER_FINALIZE, &Commissioner::HandleJoinerFinalize, this)
+    mJoinerFinalize(OT_URI_PATH_JOINER_FINALIZE, &Commissioner::HandleJoinerFinalize, this),
+    mAnnounceBegin(aInstance),
+    mEnergyScan(aInstance),
+    mPanIdQuery(aInstance)
 {
     memset(mJoiners, 0, sizeof(mJoiners));
 }
diff --git a/src/core/meshcop/commissioner.hpp b/src/core/meshcop/commissioner.hpp
index c9fb38f4e..7985ebddd 100644
--- a/src/core/meshcop/commissioner.hpp
+++ b/src/core/meshcop/commissioner.hpp
@@ -196,9 +196,29 @@ public:
     static otError GeneratePSKc(const char *aPassPhrase, const char *aNetworkName, const uint8_t *aExtPanId,
                                 uint8_t *aPSKc);
 
-    AnnounceBeginClient mAnnounceBegin;
-    EnergyScanClient mEnergyScan;
-    PanIdQueryClient mPanIdQuery;
+    /**
+     * This method returns a reference to the AnnounceBeginClient instance.
+     *
+     * @returns A reference to the AnnounceBeginClient instance.
+     *
+     */
+    AnnounceBeginClient &GetAnnounceBeginClient(void) { return mAnnounceBegin; }
+
+    /**
+     * This method returns a reference to the EnergyScanClient instance.
+     *
+     * @returns A reference to the EnergyScanClient instance.
+     *
+     */
+    EnergyScanClient &GetEnergyScanClient(void) { return mEnergyScan; }
+
+    /**
+     * This method returns a reference to the PanIdQueryClient instance.
+     *
+     * @returns A reference to the PanIdQueryClient instance.
+     *
+     */
+    PanIdQueryClient &GetPanIdQueryClient(void) { return mPanIdQuery; }
 
 private:
     enum
@@ -289,6 +309,10 @@ private:
     Coap::Resource mRelayReceive;
     Coap::Resource mDatasetChanged;
     Coap::Resource mJoinerFinalize;
+
+    AnnounceBeginClient mAnnounceBegin;
+    EnergyScanClient mEnergyScan;
+    PanIdQueryClient mPanIdQuery;
 };
 
 }  // namespace MeshCoP
diff --git a/src/core/meshcop/dataset_manager.cpp b/src/core/meshcop/dataset_manager.cpp
index d16f5cce8..fb62a3e68 100644
--- a/src/core/meshcop/dataset_manager.cpp
+++ b/src/core/meshcop/dataset_manager.cpp
@@ -62,8 +62,8 @@ namespace MeshCoP {
 DatasetManager::DatasetManager(otInstance &aInstance, const Tlv::Type aType, const char *aUriSet,
                                const char *aUriGet, Timer::Handler aTimerHandler):
     InstanceLocator(aInstance),
-    mLocal(aInstance, aType),
     mNetwork(aType),
+    mLocal(aInstance, aType),
     mTimer(aInstance, aTimerHandler, this),
     mUriSet(aUriSet),
     mUriGet(aUriGet)
diff --git a/src/core/meshcop/dataset_manager.hpp b/src/core/meshcop/dataset_manager.hpp
index d2882dbb0..1ae609b22 100644
--- a/src/core/meshcop/dataset_manager.hpp
+++ b/src/core/meshcop/dataset_manager.hpp
@@ -204,8 +204,8 @@ protected:
      */
     void HandleTimer(void);
 
-    DatasetLocal mLocal;
     Dataset mNetwork;
+    DatasetLocal mLocal;
 
 private:
     static void HandleUdpReceive(void *aContext, otMessage *aMessage, const otMessageInfo *aMessageInfo);
diff --git a/src/core/meshcop/joiner_router.cpp b/src/core/meshcop/joiner_router.cpp
index 9ed8ab494..3e7c38aa3 100644
--- a/src/core/meshcop/joiner_router.cpp
+++ b/src/core/meshcop/joiner_router.cpp
@@ -57,7 +57,7 @@ namespace MeshCoP {
 
 JoinerRouter::JoinerRouter(otInstance &aInstance):
     InstanceLocator(aInstance),
-    mSocket(aInstance.mThreadNetif.GetIp6().mUdp),
+    mSocket(aInstance.mThreadNetif.GetIp6().GetUdp()),
     mRelayTransmit(OT_URI_PATH_RELAY_TX, &JoinerRouter::HandleRelayTransmit, this),
     mTimer(aInstance, &JoinerRouter::HandleTimer, this),
     mJoinerUdpPort(0),
diff --git a/src/core/net/dhcp6_client.cpp b/src/core/net/dhcp6_client.cpp
index 57b76141a..62303db68 100644
--- a/src/core/net/dhcp6_client.cpp
+++ b/src/core/net/dhcp6_client.cpp
@@ -58,8 +58,8 @@ namespace Dhcp6 {
 
 Dhcp6Client::Dhcp6Client(otInstance &aInstance) :
     InstanceLocator(aInstance),
+    mSocket(aInstance.mThreadNetif.GetIp6().GetUdp()),
     mTrickleTimer(aInstance, &Dhcp6Client::HandleTrickleTimer, NULL, this),
-    mSocket(aInstance.mThreadNetif.GetIp6().mUdp),
     mStartTime(0),
     mAddresses(NULL),
     mNumAddresses(0)
diff --git a/src/core/net/dhcp6_client.hpp b/src/core/net/dhcp6_client.hpp
index 177682efe..257d4a004 100644
--- a/src/core/net/dhcp6_client.hpp
+++ b/src/core/net/dhcp6_client.hpp
@@ -226,10 +226,10 @@ private:
 
     static Dhcp6Client &GetOwner(const Context &aContext);
 
-    TrickleTimer mTrickleTimer;
-
     Ip6::UdpSocket mSocket;
 
+    TrickleTimer mTrickleTimer;
+
     uint8_t mTransactionId[kTransactionIdSize];
     uint32_t mStartTime;
     otDhcpAddress *mAddresses;
diff --git a/src/core/net/dhcp6_server.cpp b/src/core/net/dhcp6_server.cpp
index 81e20d038..f5bb225c6 100644
--- a/src/core/net/dhcp6_server.cpp
+++ b/src/core/net/dhcp6_server.cpp
@@ -53,7 +53,7 @@ namespace Dhcp6 {
 
 Dhcp6Server::Dhcp6Server(otInstance &aInstance):
     InstanceLocator(aInstance),
-    mSocket(GetNetif().GetIp6().mUdp)
+    mSocket(GetNetif().GetIp6().GetUdp())
 {
     for (uint8_t i = 0; i < OPENTHREAD_CONFIG_NUM_DHCP_PREFIXES; i++)
     {
diff --git a/src/core/net/dns_client.hpp b/src/core/net/dns_client.hpp
index 43034a9c4..fe546beb7 100644
--- a/src/core/net/dns_client.hpp
+++ b/src/core/net/dns_client.hpp
@@ -159,7 +159,7 @@ public:
      *
      */
     Client(Ip6::Netif &aNetif):
-        mSocket(aNetif.GetIp6().mUdp),
+        mSocket(aNetif.GetIp6().GetUdp()),
         mMessageId(0),
         mRetransmissionTimer(aNetif.GetInstance(), &Client::HandleRetransmissionTimer, this) {
     };
diff --git a/src/core/net/ip6.cpp b/src/core/net/ip6.cpp
index 172454495..0cc0dd308 100644
--- a/src/core/net/ip6.cpp
+++ b/src/core/net/ip6.cpp
@@ -52,16 +52,17 @@ namespace Ip6 {
 
 Ip6::Ip6(otInstance &aInstance):
     InstanceLocator(aInstance),
+    mForwardingEnabled(false),
+    mIsReceiveIp6FilterEnabled(false),
+    mReceiveIp6DatagramCallback(NULL),
+    mReceiveIp6DatagramCallbackContext(NULL),
+    mNetifListHead(NULL),
+    mSendQueue(),
+    mSendQueueTask(aInstance, HandleSendQueue, this),
     mRoutes(aInstance),
     mIcmp(aInstance),
     mUdp(aInstance),
-    mMpl(aInstance),
-    mForwardingEnabled(false),
-    mSendQueueTask(aInstance, HandleSendQueue, this),
-    mReceiveIp6DatagramCallback(NULL),
-    mReceiveIp6DatagramCallbackContext(NULL),
-    mIsReceiveIp6FilterEnabled(false),
-    mNetifListHead(NULL)
+    mMpl(aInstance)
 {
 }
 
diff --git a/src/core/net/ip6.hpp b/src/core/net/ip6.hpp
index c993437b8..3b57b3f80 100644
--- a/src/core/net/ip6.hpp
+++ b/src/core/net/ip6.hpp
@@ -334,6 +334,38 @@ public:
      */
     const PriorityQueue &GetSendQueue(void) const { return mSendQueue; }
 
+    /**
+     * This method returns a reference to the IPv6 route management instance.
+     *
+     * @returns A reference to the route management instance.
+     *
+     */
+    Routes &GetRoutes(void) { return mRoutes; }
+
+    /**
+     * This method returns a reference to the ICMP6 controller instance.
+     *
+     * @returns A reference to the ICMP6 instance.
+     *
+     */
+    Icmp &GetIcmp(void) { return mIcmp; }
+
+    /**
+     * This method returns a reference to the UDP controller instance.
+     *
+     * @returns A reference to the UDP instance.
+     *
+     */
+    Udp &GetUdp(void) { return mUdp; }
+
+    /**
+     * This method returns a reference to the UDMPL message processing controller instance.
+     *
+     * @returns A reference to the Mpl instance.
+     *
+     */
+    Mpl &GetMpl(void) { return mMpl; }
+
     /**
      * This static method converts an `IpProto` enumeration to a string.
      *
@@ -342,11 +374,6 @@ public:
      */
     static const char *IpProtoToString(IpProto aIpProto);
 
-    Routes mRoutes;
-    Icmp mIcmp;
-    Udp mUdp;
-    Mpl mMpl;
-
 private:
     static void HandleSendQueue(Tasklet &aTasklet);
     void HandleSendQueue(void);
@@ -367,15 +394,19 @@ private:
     static Ip6 &GetOwner(const Context &aContext);
 
     bool mForwardingEnabled;
+    bool mIsReceiveIp6FilterEnabled;
+    otIp6ReceiveCallback mReceiveIp6DatagramCallback;
+    void *mReceiveIp6DatagramCallbackContext;
+    Netif *mNetifListHead;
 
     PriorityQueue mSendQueue;
     Tasklet mSendQueueTask;
 
-    otIp6ReceiveCallback mReceiveIp6DatagramCallback;
-    void *mReceiveIp6DatagramCallbackContext;
-    bool mIsReceiveIp6FilterEnabled;
+    Routes mRoutes;
+    Icmp mIcmp;
+    Udp mUdp;
+    Mpl mMpl;
 
-    Netif *mNetifListHead;
 };
 
 /**
diff --git a/src/core/net/ip6_mpl.cpp b/src/core/net/ip6_mpl.cpp
index b46c3e64d..b146600f3 100644
--- a/src/core/net/ip6_mpl.cpp
+++ b/src/core/net/ip6_mpl.cpp
@@ -55,11 +55,11 @@ void MplBufferedMessageMetadata::GenerateNextTransmissionTime(uint32_t aCurrentT
 
 Mpl::Mpl(otInstance &aInstance):
     InstanceLocator(aInstance),
-    mSeedSetTimer(aInstance, &Mpl::HandleSeedSetTimer, this),
-    mRetransmissionTimer(aInstance, &Mpl::HandleRetransmissionTimer, this),
     mTimerExpirations(0),
     mSequence(0),
     mSeedId(0),
+    mSeedSetTimer(aInstance, &Mpl::HandleSeedSetTimer, this),
+    mRetransmissionTimer(aInstance, &Mpl::HandleRetransmissionTimer, this),
     mMatchingAddress(NULL)
 {
     memset(mSeedSet, 0, sizeof(mSeedSet));
@@ -373,7 +373,7 @@ Mpl &Mpl::GetOwner(const Context &aContext)
 #if OPENTHREAD_ENABLE_MULTIPLE_INSTANCES
     Mpl &mpl = *static_cast<Mpl *>(aContext.GetContext());
 #else
-    Mpl &mpl = otGetIp6().mMpl;
+    Mpl &mpl = otGetIp6().GetMpl();
     OT_UNUSED_VARIABLE(aContext);
 #endif
     return mpl;
diff --git a/src/core/net/ip6_mpl.hpp b/src/core/net/ip6_mpl.hpp
index 94c6db75b..711f098b7 100644
--- a/src/core/net/ip6_mpl.hpp
+++ b/src/core/net/ip6_mpl.hpp
@@ -537,12 +537,13 @@ private:
 
     static Mpl &GetOwner(const Context &aContext);
 
-    TimerMilli mSeedSetTimer;
-    TimerMilli mRetransmissionTimer;
-
     uint8_t mTimerExpirations;
     uint8_t mSequence;
     uint16_t mSeedId;
+
+    TimerMilli mSeedSetTimer;
+    TimerMilli mRetransmissionTimer;
+
     const Address *mMatchingAddress;
 
     MplSeedEntry mSeedSet[kNumSeedEntries];
diff --git a/src/core/thread/address_resolver.cpp b/src/core/thread/address_resolver.cpp
index 71ec4517b..fe31e2ac1 100644
--- a/src/core/thread/address_resolver.cpp
+++ b/src/core/thread/address_resolver.cpp
@@ -70,7 +70,7 @@ AddressResolver::AddressResolver(otInstance &aInstance) :
     GetNetif().GetCoap().AddResource(mAddressQuery);
     GetNetif().GetCoap().AddResource(mAddressNotification);
 
-    GetNetif().GetIp6().mIcmp.RegisterHandler(mIcmpHandler);
+    GetNetif().GetIp6().GetIcmp().RegisterHandler(mIcmpHandler);
 }
 
 void AddressResolver::Clear()
diff --git a/src/core/thread/data_poll_manager.cpp b/src/core/thread/data_poll_manager.cpp
index 40d934fbe..213d5dc02 100644
--- a/src/core/thread/data_poll_manager.cpp
+++ b/src/core/thread/data_poll_manager.cpp
@@ -51,10 +51,10 @@ namespace ot {
 
 DataPollManager::DataPollManager(otInstance &aInstance):
     InstanceLocator(aInstance),
-    mTimer(aInstance, &DataPollManager::HandlePollTimer, this),
     mTimerStartTime(0),
     mExternalPollPeriod(0),
     mPollPeriod(0),
+    mTimer(aInstance, &DataPollManager::HandlePollTimer, this),
     mEnabled(false),
     mAttachMode(false),
     mRetxMode(false),
diff --git a/src/core/thread/data_poll_manager.hpp b/src/core/thread/data_poll_manager.hpp
index 7cc5315f8..3731a855c 100644
--- a/src/core/thread/data_poll_manager.hpp
+++ b/src/core/thread/data_poll_manager.hpp
@@ -222,11 +222,12 @@ private:
     static DataPollManager &GetOwner(Context &aContext);
     uint32_t GetDefaultPollPeriod(void) const;
 
-    TimerMilli  mTimer;
     uint32_t    mTimerStartTime;
     uint32_t    mExternalPollPeriod;
     uint32_t    mPollPeriod;
 
+    TimerMilli  mTimer;
+
     bool        mEnabled: 1;               //< Indicates whether data polling is enabled/started.
     bool        mAttachMode: 1;            //< Indicates whether in attach mode (to use attach poll period).
     bool        mRetxMode: 1;              //< Indicates whether last poll tx failed at mac/radio layer (poll retx mode).
diff --git a/src/core/thread/mle.cpp b/src/core/thread/mle.cpp
index 1e3bb71ea..ae5618a3c 100644
--- a/src/core/thread/mle.cpp
+++ b/src/core/thread/mle.cpp
@@ -81,7 +81,7 @@ Mle::Mle(otInstance &aInstance) :
     mChildUpdateAttempts(0),
     mParentLinkMargin(0),
     mParentIsSingleton(false),
-    mSocket(aInstance.mThreadNetif.GetIp6().mUdp),
+    mSocket(aInstance.mThreadNetif.GetIp6().GetUdp()),
     mTimeout(kMleEndDeviceTimeout),
     mSendChildUpdateRequest(aInstance, &Mle::HandleSendChildUpdateRequest, this),
     mDiscoverHandler(NULL),
@@ -154,7 +154,7 @@ Mle::Mle(otInstance &aInstance) :
     mMeshLocal16.mRloc = true;
 
     // Store RLOC address reference in MPL module.
-    GetNetif().GetIp6().mMpl.SetMatchingAddress(mMeshLocal16.GetAddress());
+    GetNetif().GetIp6().GetMpl().SetMatchingAddress(mMeshLocal16.GetAddress());
 
     // link-local all thread nodes
     mLinkLocalAllThreadNodes.GetAddress().mFields.m16[0] = HostSwap16(0xff32);
@@ -583,7 +583,7 @@ otError Mle::SetStateDetached(void)
     netif.GetMac().SetBeaconEnabled(false);
     netif.GetMle().HandleDetachStart();
     netif.GetIp6().SetForwardingEnabled(false);
-    netif.GetIp6().mMpl.SetTimerExpirations(0);
+    netif.GetIp6().GetMpl().SetTimerExpirations(0);
 
     otLogInfoMle(GetInstance(), "Role -> Detached");
     return OT_ERROR_NONE;
@@ -624,7 +624,7 @@ otError Mle::SetStateChild(uint16_t aRloc16)
     netif.GetNetworkDataLocal().ClearResubmitDelayTimer();
 #endif
     netif.GetIp6().SetForwardingEnabled(false);
-    netif.GetIp6().mMpl.SetTimerExpirations(kMplChildDataMessageTimerExpirations);
+    netif.GetIp6().GetMpl().SetTimerExpirations(kMplChildDataMessageTimerExpirations);
 
     // Once the Thread device receives the new Active Commissioning Dataset, the device MUST
     // transmit its own Announce messages on the channel it was on prior to the attachment.
@@ -801,7 +801,7 @@ otError Mle::SetRloc16(uint16_t aRloc16)
     }
 
     netif.GetMac().SetShortAddress(aRloc16);
-    netif.GetIp6().mMpl.SetSeedId(aRloc16);
+    netif.GetIp6().GetMpl().SetSeedId(aRloc16);
 
     return OT_ERROR_NONE;
 }
@@ -3291,9 +3291,9 @@ otError Mle::CheckReachability(uint16_t aMeshSource, uint16_t aMeshDest, Ip6::He
     messageInfo.GetPeerAddr().mFields.m16[7] = HostSwap16(aMeshSource);
     messageInfo.SetInterfaceId(netif.GetInterfaceId());
 
-    netif.GetIp6().mIcmp.SendError(Ip6::IcmpHeader::kTypeDstUnreach,
-                                   Ip6::IcmpHeader::kCodeDstUnreachNoRoute,
-                                   messageInfo, aIp6Header);
+    netif.GetIp6().GetIcmp().SendError(Ip6::IcmpHeader::kTypeDstUnreach,
+                                       Ip6::IcmpHeader::kCodeDstUnreachNoRoute,
+                                       messageInfo, aIp6Header);
 
 exit:
     return error;
diff --git a/src/core/thread/mle_router.cpp b/src/core/thread/mle_router.cpp
index 887896e41..bc708c3cb 100644
--- a/src/core/thread/mle_router.cpp
+++ b/src/core/thread/mle_router.cpp
@@ -441,7 +441,7 @@ otError MleRouter::SetStateRouter(uint16_t aRloc16)
     netif.GetNetworkDataLeader().Stop();
     mStateUpdateTimer.Start(kStateUpdatePeriod);
     netif.GetIp6().SetForwardingEnabled(true);
-    netif.GetIp6().mMpl.SetTimerExpirations(kMplRouterDataMessageTimerExpirations);
+    netif.GetIp6().GetMpl().SetTimerExpirations(kMplRouterDataMessageTimerExpirations);
     netif.GetMac().SetBeaconEnabled(true);
 
     for (int i = 0; i < mMaxChildrenAllowed; i++)
@@ -485,7 +485,7 @@ otError MleRouter::SetStateLeader(uint16_t aRloc16)
     netif.GetCoap().AddResource(mAddressSolicit);
     netif.GetCoap().AddResource(mAddressRelease);
     netif.GetIp6().SetForwardingEnabled(true);
-    netif.GetIp6().mMpl.SetTimerExpirations(kMplRouterDataMessageTimerExpirations);
+    netif.GetIp6().GetMpl().SetTimerExpirations(kMplRouterDataMessageTimerExpirations);
     netif.GetMac().SetBeaconEnabled(true);
 
     for (int i = 0; i < mMaxChildrenAllowed; i++)
@@ -3920,9 +3920,9 @@ otError MleRouter::CheckReachability(uint16_t aMeshSource, uint16_t aMeshDest, I
     messageInfo.GetPeerAddr().mFields.m16[7] = HostSwap16(aMeshSource);
     messageInfo.SetInterfaceId(netif.GetInterfaceId());
 
-    netif.GetIp6().mIcmp.SendError(Ip6::IcmpHeader::kTypeDstUnreach,
-                                   Ip6::IcmpHeader::kCodeDstUnreachNoRoute,
-                                   messageInfo, aIp6Header);
+    netif.GetIp6().GetIcmp().SendError(Ip6::IcmpHeader::kTypeDstUnreach,
+                                       Ip6::IcmpHeader::kCodeDstUnreachNoRoute,
+                                       messageInfo, aIp6Header);
 
     return OT_ERROR_DROP;
 }
diff --git a/src/core/utils/child_supervision.cpp b/src/core/utils/child_supervision.cpp
index 5be49e136..3e25fcd4c 100644
--- a/src/core/utils/child_supervision.cpp
+++ b/src/core/utils/child_supervision.cpp
@@ -50,8 +50,8 @@ namespace Utils {
 
 ChildSupervisor::ChildSupervisor(otInstance &aInstance) :
     InstanceLocator(aInstance),
-    mTimer(aInstance, &ChildSupervisor::HandleTimer, this),
-    mSupervisionInterval(kDefaultSupervisionInterval)
+    mSupervisionInterval(kDefaultSupervisionInterval),
+    mTimer(aInstance, &ChildSupervisor::HandleTimer, this)
 {
 }
 
@@ -180,8 +180,8 @@ ChildSupervisor &ChildSupervisor::GetOwner(const Context &aContext)
 
 SupervisionListener::SupervisionListener(otInstance &aInstance) :
     InstanceLocator(aInstance),
-    mTimer(aInstance, &SupervisionListener::HandleTimer, this),
-    mTimeout(0)
+    mTimeout(0),
+    mTimer(aInstance, &SupervisionListener::HandleTimer, this)
 {
     SetTimeout(kDefaultTimeout);
 }
diff --git a/src/core/utils/child_supervision.hpp b/src/core/utils/child_supervision.hpp
index da76f107c..c6d45ccf6 100644
--- a/src/core/utils/child_supervision.hpp
+++ b/src/core/utils/child_supervision.hpp
@@ -159,8 +159,8 @@ private:
     void HandleTimer(void);
     static ChildSupervisor &GetOwner(const Context &aContext);
 
-    TimerMilli   mTimer;
     uint16_t     mSupervisionInterval;
+    TimerMilli   mTimer;
 };
 
 #else  // #if OPENTHREAD_ENABLE_CHILD_SUPERVISION && OPENTHREAD_FTD
@@ -251,8 +251,8 @@ private:
     void HandleTimer(void);
     static SupervisionListener &GetOwner(const Context &aContext);
 
-    TimerMilli mTimer;
     uint16_t mTimeout;
+    TimerMilli mTimer;
 };
 
 #else // #if OPENTHREAD_ENABLE_CHILD_SUPERVISION