diff --git a/hadoop-mapreduce-project/CHANGES.txt b/hadoop-mapreduce-project/CHANGES.txt
index 3ac103aa855..30565d03ef7 100644
--- a/hadoop-mapreduce-project/CHANGES.txt
+++ b/hadoop-mapreduce-project/CHANGES.txt
@@ -452,6 +452,9 @@ Release 0.23.1 - Unreleased
     MAPREDUCE-2450. Fixed a corner case with interrupted communication threads
     leading to a long timeout in Task. (Rajesh Balamohan via acmurthy)
 
+    MAPREDUCE-3669. Allow clients to talk to MR HistoryServer using both
+    delegation tokens and kerberos. (mahadev via acmurthy) 
+
 Release 0.23.0 - 2011-11-01 
 
   INCOMPATIBLE CHANGES
diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/java/org/apache/hadoop/mapreduce/v2/api/HSClientProtocol.java b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/java/org/apache/hadoop/mapreduce/v2/api/HSClientProtocol.java
new file mode 100644
index 00000000000..f1ea91514a7
--- /dev/null
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/java/org/apache/hadoop/mapreduce/v2/api/HSClientProtocol.java
@@ -0,0 +1,22 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.mapreduce.v2.api;
+
+public interface HSClientProtocol extends MRClientProtocol {
+}
diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/java/org/apache/hadoop/mapreduce/v2/api/impl/pb/client/HSClientProtocolPBClientImpl.java b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/java/org/apache/hadoop/mapreduce/v2/api/impl/pb/client/HSClientProtocolPBClientImpl.java
new file mode 100644
index 00000000000..c9b745002c2
--- /dev/null
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/java/org/apache/hadoop/mapreduce/v2/api/impl/pb/client/HSClientProtocolPBClientImpl.java
@@ -0,0 +1,34 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.mapreduce.v2.api.impl.pb.client;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.mapreduce.v2.api.HSClientProtocol;
+
+public class HSClientProtocolPBClientImpl extends MRClientProtocolPBClientImpl
+  implements HSClientProtocol {
+
+  public HSClientProtocolPBClientImpl(long clientVersion,
+      InetSocketAddress addr, Configuration conf) throws IOException {
+    super(clientVersion, addr, conf);
+  }
+}
\ No newline at end of file
diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/java/org/apache/hadoop/mapreduce/v2/api/impl/pb/service/HSClientProtocolPBServiceImpl.java b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/java/org/apache/hadoop/mapreduce/v2/api/impl/pb/service/HSClientProtocolPBServiceImpl.java
new file mode 100644
index 00000000000..cc9fd812784
--- /dev/null
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/java/org/apache/hadoop/mapreduce/v2/api/impl/pb/service/HSClientProtocolPBServiceImpl.java
@@ -0,0 +1,29 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.mapreduce.v2.api.impl.pb.service;
+
+import org.apache.hadoop.mapreduce.v2.api.HSClientProtocol;
+import org.apache.hadoop.yarn.proto.HSClientProtocol.HSClientProtocolService.BlockingInterface;
+
+public class HSClientProtocolPBServiceImpl extends MRClientProtocolPBServiceImpl 
+  implements BlockingInterface {
+  public HSClientProtocolPBServiceImpl(HSClientProtocol impl) {
+    super(impl);
+  } 
+}
diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/java/org/apache/hadoop/mapreduce/v2/security/client/ClientHSSecurityInfo.java b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/java/org/apache/hadoop/mapreduce/v2/security/client/ClientHSSecurityInfo.java
index f387f2123d6..f3893a99a12 100644
--- a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/java/org/apache/hadoop/mapreduce/v2/security/client/ClientHSSecurityInfo.java
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/java/org/apache/hadoop/mapreduce/v2/security/client/ClientHSSecurityInfo.java
@@ -27,14 +27,14 @@ import org.apache.hadoop.security.SecurityInfo;
 import org.apache.hadoop.security.token.TokenIdentifier;
 import org.apache.hadoop.security.token.TokenInfo;
 import org.apache.hadoop.security.token.TokenSelector;
-import org.apache.hadoop.yarn.proto.MRClientProtocol;
+import org.apache.hadoop.yarn.proto.HSClientProtocol;
 
 public class ClientHSSecurityInfo extends SecurityInfo {
   
   @Override
   public KerberosInfo getKerberosInfo(Class<?> protocol, Configuration conf) {
     if (!protocol
-        .equals(MRClientProtocol.MRClientProtocolService.BlockingInterface.class)) {
+        .equals(HSClientProtocol.HSClientProtocolService.BlockingInterface.class)) {
       return null;
     }
     return new KerberosInfo() {
@@ -59,7 +59,7 @@ public class ClientHSSecurityInfo extends SecurityInfo {
   @Override
   public TokenInfo getTokenInfo(Class<?> protocol, Configuration conf) {
     if (!protocol
-        .equals(MRClientProtocol.MRClientProtocolService.BlockingInterface.class)) {
+        .equals(HSClientProtocol.HSClientProtocolService.BlockingInterface.class)) {
       return null;
     }
     return new TokenInfo() {
diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/java/org/apache/hadoop/yarn/proto/HSClientProtocol.java b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/java/org/apache/hadoop/yarn/proto/HSClientProtocol.java
new file mode 100644
index 00000000000..574836c4e45
--- /dev/null
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/java/org/apache/hadoop/yarn/proto/HSClientProtocol.java
@@ -0,0 +1,31 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.yarn.proto;
+
+/**
+ * Fake protocol to differentiate the blocking interfaces in the 
+ * security info class loaders.
+ */
+public interface HSClientProtocol {
+  public abstract class HSClientProtocolService {
+    public interface BlockingInterface extends 
+    MRClientProtocol.MRClientProtocolService.BlockingInterface {
+    }
+  }
+}
\ No newline at end of file
diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/proto/MRClientProtocol.proto b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/proto/MRClientProtocol.proto
index 43d486e7a5d..28c8e6b7a21 100644
--- a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/proto/MRClientProtocol.proto
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/proto/MRClientProtocol.proto
@@ -22,6 +22,7 @@ option java_generic_services = true;
 
 import "mr_service_protos.proto";
 
+/* If making changes to this, please edit HSClientProtocolService */
 service MRClientProtocolService {
   rpc getJobReport (GetJobReportRequestProto) returns (GetJobReportResponseProto);
   rpc getTaskReport (GetTaskReportRequestProto) returns (GetTaskReportResponseProto);
diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/src/main/java/org/apache/hadoop/mapred/ClientCache.java b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/src/main/java/org/apache/hadoop/mapred/ClientCache.java
index 6f5a9f128ca..8db7e9783a0 100644
--- a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/src/main/java/org/apache/hadoop/mapred/ClientCache.java
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/src/main/java/org/apache/hadoop/mapred/ClientCache.java
@@ -28,6 +28,7 @@ import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.mapreduce.JobID;
+import org.apache.hadoop.mapreduce.v2.api.HSClientProtocol;
 import org.apache.hadoop.mapreduce.v2.api.MRClientProtocol;
 import org.apache.hadoop.mapreduce.v2.jobhistory.JHAdminConfig;
 import org.apache.hadoop.net.NetUtils;
@@ -91,7 +92,7 @@ public class ClientCache {
     return currentUser.doAs(new PrivilegedAction<MRClientProtocol>() {
       @Override
       public MRClientProtocol run() {
-        return (MRClientProtocol) rpc.getProxy(MRClientProtocol.class,
+        return (MRClientProtocol) rpc.getProxy(HSClientProtocol.class,
             NetUtils.createSocketAddr(serviceAddr), conf);
       }
     });