diff --git a/hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/resolver/MountTableResolver.java b/hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/resolver/MountTableResolver.java
index 9e69840af9c..da585515c35 100644
--- a/hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/resolver/MountTableResolver.java
+++ b/hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/resolver/MountTableResolver.java
@@ -17,8 +17,6 @@
  */
 package org.apache.hadoop.hdfs.server.federation.resolver;
 
-import static org.apache.hadoop.hdfs.client.HdfsClientConfigKeys.DFS_NAMESERVICES;
-import static org.apache.hadoop.hdfs.client.HdfsClientConfigKeys.DeprecatedKeys.DFS_NAMESERVICE_ID;
 import static org.apache.hadoop.hdfs.server.federation.router.RBFConfigKeys.DFS_ROUTER_DEFAULT_NAMESERVICE;
 import static org.apache.hadoop.hdfs.server.federation.router.RBFConfigKeys.DFS_ROUTER_DEFAULT_NAMESERVICE_ENABLE;
 import static org.apache.hadoop.hdfs.server.federation.router.RBFConfigKeys.DFS_ROUTER_DEFAULT_NAMESERVICE_ENABLE_DEFAULT;
@@ -50,8 +48,6 @@ import java.util.concurrent.locks.ReentrantReadWriteLock;
 
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.Path;
-import org.apache.hadoop.hdfs.DFSUtil;
-import org.apache.hadoop.hdfs.DFSUtilClient;
 import org.apache.hadoop.hdfs.server.federation.resolver.order.DestinationOrder;
 import org.apache.hadoop.hdfs.server.federation.router.Router;
 import org.apache.hadoop.hdfs.server.federation.store.MountTableStore;
@@ -163,33 +159,22 @@ public class MountTableResolver
    * @param conf Configuration for this resolver.
    */
   private void initDefaultNameService(Configuration conf) {
-    this.defaultNameService = conf.get(
-        DFS_ROUTER_DEFAULT_NAMESERVICE,
-        DFSUtil.getNamenodeNameServiceId(conf));
-
     this.defaultNSEnable = conf.getBoolean(
         DFS_ROUTER_DEFAULT_NAMESERVICE_ENABLE,
         DFS_ROUTER_DEFAULT_NAMESERVICE_ENABLE_DEFAULT);
 
-    if (defaultNameService == null) {
-      LOG.warn(
-          "{} and {} is not set. Fallback to {} as the default name service.",
-          DFS_ROUTER_DEFAULT_NAMESERVICE, DFS_NAMESERVICE_ID, DFS_NAMESERVICES);
-      Collection<String> nsIds = DFSUtilClient.getNameServiceIds(conf);
-      if (nsIds.isEmpty()) {
-        this.defaultNameService = "";
-      } else {
-        this.defaultNameService = nsIds.iterator().next();
-      }
+    if (!this.defaultNSEnable) {
+      LOG.warn("Default name service is disabled.");
+      return;
     }
+    this.defaultNameService = conf.get(DFS_ROUTER_DEFAULT_NAMESERVICE, "");
 
     if (this.defaultNameService.equals("")) {
       this.defaultNSEnable = false;
       LOG.warn("Default name service is not set.");
     } else {
-      String enable = this.defaultNSEnable ? "enabled" : "disabled";
-      LOG.info("Default name service: {}, {} to read or write",
-          this.defaultNameService, enable);
+      LOG.info("Default name service: {}, enabled to read or write",
+          this.defaultNameService);
     }
   }
 
diff --git a/hadoop-hdfs-project/hadoop-hdfs-rbf/src/test/java/org/apache/hadoop/hdfs/server/federation/resolver/TestInitializeMountTableResolver.java b/hadoop-hdfs-project/hadoop-hdfs-rbf/src/test/java/org/apache/hadoop/hdfs/server/federation/resolver/TestInitializeMountTableResolver.java
index 5db7531c4dd..8a22ade0743 100644
--- a/hadoop-hdfs-project/hadoop-hdfs-rbf/src/test/java/org/apache/hadoop/hdfs/server/federation/resolver/TestInitializeMountTableResolver.java
+++ b/hadoop-hdfs-project/hadoop-hdfs-rbf/src/test/java/org/apache/hadoop/hdfs/server/federation/resolver/TestInitializeMountTableResolver.java
@@ -23,7 +23,9 @@ import org.junit.Test;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMESERVICE_ID;
 import static org.apache.hadoop.hdfs.client.HdfsClientConfigKeys.DFS_NAMESERVICES;
 import static org.apache.hadoop.hdfs.server.federation.router.RBFConfigKeys.DFS_ROUTER_DEFAULT_NAMESERVICE;
+import static org.apache.hadoop.hdfs.server.federation.router.RBFConfigKeys.DFS_ROUTER_DEFAULT_NAMESERVICE_ENABLE;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
 
 /**
  * Test {@link MountTableResolver} initialization.
@@ -43,40 +45,26 @@ public class TestInitializeMountTableResolver {
     conf.set(DFS_ROUTER_DEFAULT_NAMESERVICE, "");
     MountTableResolver mountTable = new MountTableResolver(conf);
     assertEquals("", mountTable.getDefaultNamespace());
+    assertFalse("Default NS should be disabled if default NS is set empty",
+        mountTable.isDefaultNSEnable());
   }
 
   @Test
   public void testRouterDefaultNameservice() {
     Configuration conf = new Configuration();
-    conf.set(DFS_ROUTER_DEFAULT_NAMESERVICE, "router_ns"); // this is priority
-    conf.set(DFS_NAMESERVICE_ID, "ns_id");
-    conf.set(DFS_NAMESERVICES, "nss");
+    conf.set(DFS_ROUTER_DEFAULT_NAMESERVICE, "router_ns");
     MountTableResolver mountTable = new MountTableResolver(conf);
     assertEquals("router_ns", mountTable.getDefaultNamespace());
   }
 
+  // Default NS should be empty if configured false.
   @Test
-  public void testNameserviceID() {
+  public void testRouterDefaultNameserviceDisabled() {
     Configuration conf = new Configuration();
-    conf.set(DFS_NAMESERVICE_ID, "ns_id"); // this is priority
+    conf.setBoolean(DFS_ROUTER_DEFAULT_NAMESERVICE_ENABLE, false);
+    conf.set(DFS_NAMESERVICE_ID, "ns_id");
     conf.set(DFS_NAMESERVICES, "nss");
     MountTableResolver mountTable = new MountTableResolver(conf);
-    assertEquals("ns_id", mountTable.getDefaultNamespace());
-  }
-
-  @Test
-  public void testSingleNameservices() {
-    Configuration conf = new Configuration();
-    conf.set(DFS_NAMESERVICES, "ns1");
-    MountTableResolver mountTable = new MountTableResolver(conf);
-    assertEquals("ns1", mountTable.getDefaultNamespace());
-  }
-
-  @Test
-  public void testMultipleNameservices() {
-    Configuration conf = new Configuration();
-    conf.set(DFS_NAMESERVICES, "ns1,ns2");
-    MountTableResolver mountTable = new MountTableResolver(conf);
-    assertEquals("ns1", mountTable.getDefaultNamespace());
+    assertEquals("", mountTable.getDefaultNamespace());
   }
 }
\ No newline at end of file