diff --git a/include/openthread/dns.h b/include/openthread/dns.h
index 341cb21c5..4aa990cbb 100644
--- a/include/openthread/dns.h
+++ b/include/openthread/dns.h
@@ -35,6 +35,12 @@
 #ifndef OPENTHREAD_DNS_H_
 #define OPENTHREAD_DNS_H_
 
+#ifdef OPENTHREAD_CONFIG_FILE
+#include OPENTHREAD_CONFIG_FILE
+#else
+#include <openthread-config.h>
+#endif
+
 #include <openthread/types.h>
 #include <openthread/message.h>
 
diff --git a/src/core/api/coap_api.cpp b/src/core/api/coap_api.cpp
index beacdd5d9..d54c9fe35 100644
--- a/src/core/api/coap_api.cpp
+++ b/src/core/api/coap_api.cpp
@@ -38,8 +38,6 @@
 
 using namespace Thread;
 
-extern "C" {
-
 void otCoapHeaderInit(otCoapHeader *aHeader, otCoapType aType, otCoapCode aCode)
 {
     Coap::Header *header = static_cast<Coap::Header *>(aHeader);
@@ -170,5 +168,3 @@ ThreadError otCoapSendResponse(otInstance *aInstance, otMessage *aMessage, const
     return aInstance->mApplicationCoapServer.SendMessage(
                *static_cast<Message *>(aMessage), *static_cast<const Ip6::MessageInfo *>(aMessageInfo));
 }
-
-}  // extern "C"
diff --git a/src/core/api/commissioner_api.cpp b/src/core/api/commissioner_api.cpp
index 14c05f61c..978ac3d53 100644
--- a/src/core/api/commissioner_api.cpp
+++ b/src/core/api/commissioner_api.cpp
@@ -37,10 +37,6 @@
 
 using namespace Thread;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #if OPENTHREAD_ENABLE_COMMISSIONER
 
 ThreadError otCommissionerStart(otInstance *aInstance)
@@ -122,7 +118,3 @@ ThreadError otCommissionerGeneratePSKc(otInstance *aInstance, const char *aPassP
 }
 
 #endif  // OPENTHREAD_ENABLE_COMMISSIONER
-
-#ifdef __cplusplus
-}  // extern "C"
-#endif
diff --git a/src/core/api/crypto_api.cpp b/src/core/api/crypto_api.cpp
index f5b96ac80..ca1edc45b 100644
--- a/src/core/api/crypto_api.cpp
+++ b/src/core/api/crypto_api.cpp
@@ -40,10 +40,6 @@
 
 using namespace Thread::Crypto;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 void otCryptoHmacSha256(
     const uint8_t *aKey, uint16_t aKeyLength,
     const uint8_t *aBuf, uint16_t aBufLength,
@@ -88,7 +84,3 @@ void otCryptoAesCcm(
 exit:
     return;
 }
-
-#ifdef __cplusplus
-}  // extern "C"
-#endif
diff --git a/src/core/api/dataset_api.cpp b/src/core/api/dataset_api.cpp
index c9f239dea..7c24f0013 100644
--- a/src/core/api/dataset_api.cpp
+++ b/src/core/api/dataset_api.cpp
@@ -37,10 +37,6 @@
 
 using namespace Thread;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 bool otDatasetIsCommissioned(otInstance *aInstance)
 {
     otOperationalDataset dataset;
@@ -137,7 +133,3 @@ ThreadError otDatasetSetDelayTimerMinimal(otInstance *aInstance, uint32_t aDelay
 {
     return aInstance->mThreadNetif.GetLeader().SetDelayTimerMinimal(aDelayTimerMinimal);
 }
-
-#ifdef __cplusplus
-}  // extern "C"
-#endif
diff --git a/src/core/api/dhcp6_api.cpp b/src/core/api/dhcp6_api.cpp
index 5af1f4538..ef5a1b14c 100644
--- a/src/core/api/dhcp6_api.cpp
+++ b/src/core/api/dhcp6_api.cpp
@@ -38,10 +38,6 @@
 
 using namespace Thread;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #if OPENTHREAD_ENABLE_DHCP6_CLIENT
 void otDhcp6ClientUpdate(otInstance *aInstance, otDhcpAddress *aAddresses, uint32_t aNumAddresses, void *aContext)
 {
@@ -55,7 +51,3 @@ void otDhcp6ServerUpdate(otInstance *aInstance)
     aInstance->mThreadNetif.GetDhcp6Server().UpdateService();
 }
 #endif  // OPENTHREAD_ENABLE_DHCP6_SERVER
-
-#ifdef __cplusplus
-}  // extern "C"
-#endif
diff --git a/src/core/api/dns_api.cpp b/src/core/api/dns_api.cpp
index e873d1935..89f6d05eb 100644
--- a/src/core/api/dns_api.cpp
+++ b/src/core/api/dns_api.cpp
@@ -37,10 +37,6 @@
 
 using namespace Thread;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #if OPENTHREAD_ENABLE_DNS_CLIENT
 ThreadError otDnsClientQuery(otInstance *aInstance, const otDnsQuery *aQuery, otDnsResponseHandler aHandler,
                              void *aContext)
@@ -48,7 +44,3 @@ ThreadError otDnsClientQuery(otInstance *aInstance, const otDnsQuery *aQuery, ot
     return aInstance->mThreadNetif.GetDnsClient().Query(aQuery, aHandler, aContext);
 }
 #endif  // OPENTHREAD_ENABLE_DNS_CLIENT
-
-#ifdef __cplusplus
-}  // extern "C"
-#endif
diff --git a/src/core/api/icmp6_api.cpp b/src/core/api/icmp6_api.cpp
index 6cba28d83..d0c30c581 100644
--- a/src/core/api/icmp6_api.cpp
+++ b/src/core/api/icmp6_api.cpp
@@ -37,10 +37,6 @@
 
 using namespace Thread;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 bool otIcmp6IsEchoEnabled(otInstance *aInstance)
 {
     return aInstance->mIp6.mIcmp.IsEchoEnabled();
@@ -63,7 +59,3 @@ ThreadError otIcmp6SendEchoRequest(otInstance *aInstance, otMessage *aMessage,
                                                  *static_cast<const Ip6::MessageInfo *>(aMessageInfo),
                                                  aIdentifier);
 }
-
-#ifdef __cplusplus
-}  // extern "C"
-#endif
diff --git a/src/core/api/instance_api.cpp b/src/core/api/instance_api.cpp
index a345a0684..fbbd8215e 100644
--- a/src/core/api/instance_api.cpp
+++ b/src/core/api/instance_api.cpp
@@ -75,10 +75,6 @@ otInstance::otInstance(void) :
 
 using namespace Thread;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 void otInstancePostConstructor(otInstance *aInstance)
 {
     // restore datasets and network information
@@ -251,7 +247,3 @@ ThreadError otSetDynamicLogLevel(otInstance *aInstance, otLogLevel aLogLevel)
 
     return error;
 }
-
-#ifdef __cplusplus
-}  // extern "C"
-#endif
diff --git a/src/core/api/ip6_api.cpp b/src/core/api/ip6_api.cpp
index df2d5d88e..73aaa2644 100644
--- a/src/core/api/ip6_api.cpp
+++ b/src/core/api/ip6_api.cpp
@@ -41,10 +41,6 @@
 
 using namespace Thread;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 ThreadError otIp6SetEnabled(otInstance *aInstance, bool aEnabled)
 {
     ThreadError error = kThreadError_None;
@@ -220,7 +216,3 @@ uint8_t otIp6PrefixMatch(const otIp6Address *aFirst, const otIp6Address *aSecond
 exit:
     return rval;
 }
-
-#ifdef __cplusplus
-}  // extern "C"
-#endif
diff --git a/src/core/api/jam_detection_api.cpp b/src/core/api/jam_detection_api.cpp
index 8a1f982f7..ac5338192 100644
--- a/src/core/api/jam_detection_api.cpp
+++ b/src/core/api/jam_detection_api.cpp
@@ -37,10 +37,6 @@
 
 using namespace Thread;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #if OPENTHREAD_ENABLE_JAM_DETECTION
 
 ThreadError otJamDetectionSetRssiThreshold(otInstance *aInstance, int8_t aRssiThreshold)
@@ -99,7 +95,3 @@ uint64_t otJamDetectionGetHistoryBitmap(otInstance *aInstance)
 }
 
 #endif  // OPENTHREAD_ENABLE_JAM_DETECTION
-
-#ifdef __cplusplus
-}  // extern "C"
-#endif
diff --git a/src/core/api/joiner_api.cpp b/src/core/api/joiner_api.cpp
index f6e8021a3..8f6493965 100644
--- a/src/core/api/joiner_api.cpp
+++ b/src/core/api/joiner_api.cpp
@@ -37,10 +37,6 @@
 
 using namespace Thread;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #if OPENTHREAD_ENABLE_JOINER
 
 ThreadError otJoinerStart(otInstance *aInstance, const char *aPSKd, const char *aProvisioningUrl,
@@ -59,7 +55,3 @@ ThreadError otJoinerStop(otInstance *aInstance)
 }
 
 #endif  // OPENTHREAD_ENABLE_JOINER
-
-#ifdef __cplusplus
-}  // extern "C"
-#endif
diff --git a/src/core/api/link_api.cpp b/src/core/api/link_api.cpp
index d7f0101f3..66a24b91b 100644
--- a/src/core/api/link_api.cpp
+++ b/src/core/api/link_api.cpp
@@ -37,10 +37,6 @@
 
 using namespace Thread;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 static void HandleActiveScanResult(void *aContext, Mac::Frame *aFrame);
 static void HandleEnergyScanResult(void *aContext, otEnergyScanResult *aResult);
 
@@ -376,8 +372,3 @@ bool otLinkIsInTransmitState(otInstance *aInstance)
 {
     return aInstance->mThreadNetif.GetMac().IsInTransmitState();
 }
-
-
-#ifdef __cplusplus
-}  // extern "C"
-#endif
diff --git a/src/core/api/link_raw_api.cpp b/src/core/api/link_raw_api.cpp
index 5bad288e1..50718cfcc 100644
--- a/src/core/api/link_raw_api.cpp
+++ b/src/core/api/link_raw_api.cpp
@@ -37,10 +37,6 @@
 #include "openthread/platform/usec-alarm.h"
 #include "openthread-instance.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 ThreadError otLinkRawSetEnable(otInstance *aInstance, bool aEnabled)
 {
     ThreadError error = kThreadError_None;
@@ -259,10 +255,6 @@ exit:
     return error;
 }
 
-#ifdef __cplusplus
-}  // extern "C"
-#endif
-
 namespace Thread {
 
 LinkRaw::LinkRaw(otInstance &aInstance):
diff --git a/src/core/api/message_api.cpp b/src/core/api/message_api.cpp
index 07989d5f1..d998a2a82 100644
--- a/src/core/api/message_api.cpp
+++ b/src/core/api/message_api.cpp
@@ -37,10 +37,6 @@
 
 using namespace Thread;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 ThreadError otMessageFree(otMessage *aMessage)
 {
     return static_cast<Message *>(aMessage)->Free();
@@ -177,7 +173,3 @@ void otMessageGetBufferInfo(otInstance *aInstance, otBufferInfo *aBufferInfo)
     aInstance->mThreadNetif.GetCoapServer().GetCachedResponses().GetInfo(aBufferInfo->mCoapServerMessages,
                                                                          aBufferInfo->mCoapServerBuffers);
 }
-
-#ifdef __cplusplus
-}  // extern "C"
-#endif
diff --git a/src/core/api/netdata_api.cpp b/src/core/api/netdata_api.cpp
index 257600760..38d19a921 100644
--- a/src/core/api/netdata_api.cpp
+++ b/src/core/api/netdata_api.cpp
@@ -37,10 +37,6 @@
 
 using namespace Thread;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 ThreadError otNetDataGetLeader(otInstance *aInstance, bool aStable, uint8_t *aData, uint8_t *aDataLength)
 {
     ThreadError error = kThreadError_None;
@@ -156,7 +152,3 @@ uint8_t otNetDataGetStableVersion(otInstance *aInstance)
 {
     return aInstance->mThreadNetif.GetMle().GetLeaderDataTlv().GetStableDataVersion();
 }
-
-#ifdef __cplusplus
-}  // extern "C"
-#endif
diff --git a/src/core/api/tasklet_api.cpp b/src/core/api/tasklet_api.cpp
index 92b31f010..3105c6b0d 100644
--- a/src/core/api/tasklet_api.cpp
+++ b/src/core/api/tasklet_api.cpp
@@ -40,10 +40,6 @@
 
 using namespace Thread;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 void otTaskletsProcess(otInstance *aInstance)
 {
     otLogFuncEntry();
@@ -55,7 +51,3 @@ bool otTaskletsArePending(otInstance *aInstance)
 {
     return aInstance->mIp6.mTaskletScheduler.AreTaskletsPending();
 }
-
-#ifdef __cplusplus
-}  // extern "C"
-#endif
diff --git a/src/core/api/thread_api.cpp b/src/core/api/thread_api.cpp
index 8416631f1..1cd8ff6a5 100644
--- a/src/core/api/thread_api.cpp
+++ b/src/core/api/thread_api.cpp
@@ -42,10 +42,6 @@
 
 using namespace Thread;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 uint8_t otThreadGetMaxAllowedChildren(otInstance *aInstance)
 {
     uint8_t aNumChildren;
@@ -702,7 +698,3 @@ bool otThreadIsDiscoverInProgress(otInstance *aInstance)
 {
     return aInstance->mThreadNetif.GetMle().IsDiscoverInProgress();
 }
-
-#ifdef __cplusplus
-}  // extern "C"
-#endif
diff --git a/src/core/api/udp_api.cpp b/src/core/api/udp_api.cpp
index 8cdec01d6..6dad06439 100644
--- a/src/core/api/udp_api.cpp
+++ b/src/core/api/udp_api.cpp
@@ -37,10 +37,6 @@
 
 using namespace Thread;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 otMessage *otUdpNewMessage(otInstance *aInstance, bool aLinkSecurityEnabled)
 {
     Message *message = aInstance->mIp6.mUdp.NewMessage(0);
@@ -103,7 +99,3 @@ ThreadError otUdpSend(otUdpSocket *aSocket, otMessage *aMessage, const otMessage
     return socket->SendTo(*static_cast<Message *>(aMessage),
                           *static_cast<const Ip6::MessageInfo *>(aMessageInfo));
 }
-
-#ifdef __cplusplus
-}  // extern "C"
-#endif
diff --git a/src/core/crypto/pbkdf2_cmac.cpp b/src/core/crypto/pbkdf2_cmac.cpp
index 518569276..eff761e5f 100644
--- a/src/core/crypto/pbkdf2_cmac.cpp
+++ b/src/core/crypto/pbkdf2_cmac.cpp
@@ -35,13 +35,6 @@
 #include <crypto/pbkdf2_cmac.h>
 #include <mbedtls/cmac.h>
 
-namespace Thread {
-namespace Crypto {
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 void otPbkdf2Cmac(
     const uint8_t *aPassword, uint16_t aPasswordLen,
     const uint8_t *aSalt, uint16_t aSaltLen,
@@ -91,10 +84,3 @@ void otPbkdf2Cmac(
         keyLen -= useLen;
     }
 }
-
-#ifdef __cplusplus
-}  // extern "C"
-#endif
-
-}  // namespace Crypto
-}  // namespace Thread
diff --git a/src/diag/openthread-diag.cpp b/src/diag/openthread-diag.cpp
index 37ef8a12d..d7b71889d 100644
--- a/src/diag/openthread-diag.cpp
+++ b/src/diag/openthread-diag.cpp
@@ -40,10 +40,6 @@
 
 using namespace Thread::Diagnostics;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 void otDiagInit(otInstance *aInstance)
 {
     Diag::Init(aInstance);
@@ -83,7 +79,3 @@ bool otDiagIsEnabled()
 {
     return Diag::isEnabled();
 }
-
-#ifdef __cplusplus
-}  // extern "C"
-#endif