diff --git a/core/api/src/main/java/org/onosproject/core/DefaultGroupId.java b/core/api/src/main/java/org/onosproject/core/DefaultGroupId.java
index 7467c3c..3f95559 100644
--- a/core/api/src/main/java/org/onosproject/core/DefaultGroupId.java
+++ b/core/api/src/main/java/org/onosproject/core/DefaultGroupId.java
@@ -61,7 +61,7 @@
     @Override
     public String toString() {
         return MoreObjects.toStringHelper(this)
-                .add("id", id)
+                .add("id", "0x" + Integer.toHexString(id))
                 .toString();
     }
 }
diff --git a/core/api/src/main/java/org/onosproject/net/flow/instructions/Instructions.java b/core/api/src/main/java/org/onosproject/net/flow/instructions/Instructions.java
index e1a71fc..3e2335b 100644
--- a/core/api/src/main/java/org/onosproject/net/flow/instructions/Instructions.java
+++ b/core/api/src/main/java/org/onosproject/net/flow/instructions/Instructions.java
@@ -576,7 +576,7 @@
 
         @Override
         public String toString() {
-            return type().toString() + SEPARATOR + Integer.toHexString(groupId.id());
+            return type().toString() + SEPARATOR + "0x" + Integer.toHexString(groupId.id());
         }
 
         @Override
diff --git a/core/api/src/main/java/org/onosproject/net/group/GroupOperation.java b/core/api/src/main/java/org/onosproject/net/group/GroupOperation.java
index e4173b3..42ef9dd 100644
--- a/core/api/src/main/java/org/onosproject/net/group/GroupOperation.java
+++ b/core/api/src/main/java/org/onosproject/net/group/GroupOperation.java
@@ -31,6 +31,7 @@
     private final GroupId groupId;
     private final GroupDescription.Type groupType;
     private final GroupBuckets buckets;
+    private final GroupMsgErrorCode failureCode;
 
     public enum Type {
         /**
@@ -48,6 +49,28 @@
     }
 
     /**
+     * Possible error codes for a failure of a group operation.
+     *
+     */
+    public enum GroupMsgErrorCode {
+        GROUP_EXISTS,
+        INVALID_GROUP,
+        WEIGHT_UNSUPPORTED,
+        OUT_OF_GROUPS,
+        OUT_OF_BUCKETS,
+        CHAINING_UNSUPPORTED,
+        WATCH_UNSUPPORTED,
+        LOOP,
+        UNKNOWN_GROUP,
+        CHAINED_GROUP,
+        BAD_TYPE,
+        BAD_COMMAND,
+        BAD_BUCKET,
+        BAD_WATCH,
+        EPERM;
+    }
+
+    /**
      * Group operation constructor with the parameters.
      *
      * @param opType group operation type
@@ -63,6 +86,23 @@
         this.groupId = checkNotNull(groupId);
         this.groupType = checkNotNull(groupType);
         this.buckets = buckets;
+        this.failureCode = null;
+    }
+
+    /**
+     * Group operation copy-constructor with additional field to set failure code.
+     * Typically used by provider to return information to the core about
+     * the failure reason for a group operation.
+     *
+     * @param groupOp the original group operation
+     * @param failureCode failure code for a failed group operation
+     */
+    private GroupOperation(GroupOperation groupOp, GroupMsgErrorCode failureCode) {
+        this.opType = groupOp.opType;
+        this.groupId = groupOp.groupId;
+        this.groupType = groupOp.groupType;
+        this.buckets = groupOp.buckets;
+        this.failureCode = failureCode;
     }
 
     /**
@@ -109,6 +149,12 @@
 
     }
 
+    public static GroupOperation createFailedGroupOperation(GroupOperation groupOperation,
+                                                            GroupMsgErrorCode failureCode) {
+        checkNotNull(groupOperation);
+        return new GroupOperation(groupOperation, failureCode);
+    }
+
     /**
      * Returns group operation type.
      *
@@ -145,6 +191,15 @@
         return this.buckets;
     }
 
+    /**
+     * Returns the failure code representing the failure of a group operation.
+     *
+     * @return error code for failure of group operation
+     */
+    public GroupMsgErrorCode failureCode() {
+        return failureCode;
+    }
+
     @Override
     /*
      * The deviceId, type and buckets are used for hash.