diff --git a/staticlibs/client-libs/Android.bp b/staticlibs/client-libs/Android.bp
index f6d781c..e1a1086 100644
--- a/staticlibs/client-libs/Android.bp
+++ b/staticlibs/client-libs/Android.bp
@@ -9,7 +9,9 @@
     ],
     visibility: [
         "//packages/modules/Connectivity/Tethering",
-        "//frameworks/base/services:__subpackages__"
+        "//frameworks/base/services:__subpackages__",
+        "//frameworks/base/packages:__subpackages__",
+        "//frameworks/libs/net/client-libs/tests:__subpackages__",
     ],
     libs: ["androidx.annotation_annotation"],
     static_libs: [
diff --git a/staticlibs/client-libs/netd/com/android/net/module/util/NetdUtils.java b/staticlibs/client-libs/netd/com/android/net/module/util/NetdUtils.java
new file mode 100644
index 0000000..1f31912
--- /dev/null
+++ b/staticlibs/client-libs/netd/com/android/net/module/util/NetdUtils.java
@@ -0,0 +1,105 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed 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 com.android.net.module.util;
+
+import static android.net.INetd.IF_STATE_DOWN;
+import static android.net.INetd.IF_STATE_UP;
+
+import android.net.INetd;
+import android.net.InterfaceConfigurationParcel;
+import android.os.RemoteException;
+import android.os.ServiceSpecificException;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.VisibleForTesting;
+
+import java.util.ArrayList;
+
+/**
+ * Collection of utilities for netd.
+ */
+public class NetdUtils {
+    /**
+     * Get InterfaceConfigurationParcel from netd.
+     */
+    public static InterfaceConfigurationParcel getInterfaceConfigParcel(@NonNull INetd netd,
+            @NonNull String iface) {
+        try {
+            return netd.interfaceGetCfg(iface);
+        } catch (RemoteException | ServiceSpecificException e) {
+            throw new IllegalStateException(e);
+        }
+    }
+
+    private static void validateFlag(String flag) {
+        if (flag.indexOf(' ') >= 0) {
+            throw new IllegalArgumentException("flag contains space: " + flag);
+        }
+    }
+
+    @VisibleForTesting
+    protected static String[] removeAndAddFlags(@NonNull String[] flags, @NonNull String remove,
+            @NonNull String add) {
+        final ArrayList<String> result = new ArrayList<>();
+        try {
+            // Validate the add flag first, so that the for-loop can be ignore once the format of
+            // add flag is invalid.
+            validateFlag(add);
+            for (String flag : flags) {
+                // Simply ignore both of remove and add flags first, then add the add flag after
+                // exiting the loop to prevent adding the duplicate flag.
+                if (remove.equals(flag) || add.equals(flag)) continue;
+                result.add(flag);
+            }
+            result.add(add);
+            return result.toArray(new String[result.size()]);
+        } catch (IllegalArgumentException iae) {
+            throw new IllegalStateException("Invalid InterfaceConfigurationParcel", iae);
+        }
+    }
+
+    /**
+     * Set interface configuration to netd by passing InterfaceConfigurationParcel.
+     */
+    public static void setInterfaceConfig(INetd netd, InterfaceConfigurationParcel configParcel) {
+        try {
+            netd.interfaceSetCfg(configParcel);
+        } catch (RemoteException | ServiceSpecificException e) {
+            throw new IllegalStateException(e);
+        }
+    }
+
+    /**
+     * Set the given interface up.
+     */
+    public static void setInterfaceUp(INetd netd, String iface) {
+        final InterfaceConfigurationParcel configParcel = getInterfaceConfigParcel(netd, iface);
+        configParcel.flags = removeAndAddFlags(configParcel.flags, IF_STATE_DOWN /* remove */,
+                IF_STATE_UP /* add */);
+        setInterfaceConfig(netd, configParcel);
+    }
+
+    /**
+     * Set the given interface down.
+     */
+    public static void setInterfaceDown(INetd netd, String iface) {
+        final InterfaceConfigurationParcel configParcel = getInterfaceConfigParcel(netd, iface);
+        configParcel.flags = removeAndAddFlags(configParcel.flags, IF_STATE_UP /* remove */,
+                IF_STATE_DOWN /* add */);
+        setInterfaceConfig(netd, configParcel);
+    }
+}
diff --git a/staticlibs/client-libs/tests/unit/Android.bp b/staticlibs/client-libs/tests/unit/Android.bp
new file mode 100644
index 0000000..fc8a2c6
--- /dev/null
+++ b/staticlibs/client-libs/tests/unit/Android.bp
@@ -0,0 +1,39 @@
+android_library {
+    name: "NetdStaticLibTestsLib",
+    srcs: [
+        "src/**/*.java",
+        "src/**/*.kt",
+    ],
+    min_sdk_version: "29",
+    static_libs: [
+        "androidx.test.rules",
+        "mockito-target-extended-minus-junit4",
+        "net-tests-utils-host-device-common",
+        "netd-client",
+    ],
+    libs: [
+        "android.test.runner",
+        "android.test.base",
+    ],
+    visibility: [
+        // Visible for Tethering and NetworkStack integration test and link NetdStaticLibTestsLib
+        // there, so that the tests under client-libs can also be run when running tethering and
+        // NetworkStack MTS.
+        "//packages/modules/Connectivity/Tethering/tests/integration",
+        "//packages/modules/NetworkStack/tests/integration",
+    ]
+}
+
+android_test {
+    name: "NetdStaticLibTests",
+    certificate: "platform",
+    static_libs: [
+        "NetdStaticLibTestsLib",
+    ],
+    jni_libs: [
+        // For mockito extended
+        "libdexmakerjvmtiagent",
+        "libstaticjvmtiagent",
+    ],
+    test_suites: ["device-tests"],
+}
diff --git a/staticlibs/client-libs/tests/unit/AndroidManifest.xml b/staticlibs/client-libs/tests/unit/AndroidManifest.xml
new file mode 100644
index 0000000..7a07d3d
--- /dev/null
+++ b/staticlibs/client-libs/tests/unit/AndroidManifest.xml
@@ -0,0 +1,28 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (C) 2021 The Android Open Source Project
+
+     Licensed 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.
+-->
+
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+        package="com.android.frameworks.clientlibs.tests">
+
+    <application android:debuggable="true">
+        <uses-library android:name="android.test.runner" />
+    </application>
+
+    <instrumentation
+        android:name="androidx.test.runner.AndroidJUnitRunner"
+        android:targetPackage="com.android.frameworks.clientlibs.tests"
+        android:label="Netd Static Library Tests" />
+</manifest>
diff --git a/staticlibs/client-libs/tests/unit/src/com/android/net/module/util/NetdUtilsTest.java b/staticlibs/client-libs/tests/unit/src/com/android/net/module/util/NetdUtilsTest.java
new file mode 100644
index 0000000..306b1bb
--- /dev/null
+++ b/staticlibs/client-libs/tests/unit/src/com/android/net/module/util/NetdUtilsTest.java
@@ -0,0 +1,103 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed 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 com.android.net.module.util;
+
+import static com.android.testutils.MiscAsserts.assertThrows;
+
+import static org.mockito.ArgumentMatchers.argThat;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import android.net.INetd;
+import android.net.InterfaceConfigurationParcel;
+
+import androidx.test.filters.SmallTest;
+import androidx.test.runner.AndroidJUnit4;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+import java.util.Arrays;
+
+@RunWith(AndroidJUnit4.class)
+@SmallTest
+public class NetdUtilsTest {
+    @Mock private INetd mNetd;
+
+    private static final String IFACE = "TEST_IFACE";
+
+    @Before
+    public void setUp() throws Exception {
+        MockitoAnnotations.initMocks(this);
+    }
+
+    private void setupFlagsForInterfaceConfiguration(String[] flags) throws Exception {
+        final InterfaceConfigurationParcel config = new InterfaceConfigurationParcel();
+        config.flags = flags;
+        when(mNetd.interfaceGetCfg(eq(IFACE))).thenReturn(config);
+    }
+
+    private void verifyMethodsAndArgumentsOfSetInterface(boolean ifaceUp) throws Exception {
+        final String[] flagsContainDownAndUp = new String[] {"flagA", "down", "flagB", "up"};
+        final String[] flagsForInterfaceDown = new String[] {"flagA", "down", "flagB"};
+        final String[] flagsForInterfaceUp = new String[] {"flagA", "up", "flagB"};
+        final String[] expectedFinalFlags;
+        setupFlagsForInterfaceConfiguration(flagsContainDownAndUp);
+        if (ifaceUp) {
+            // "down" flag will be removed from flagsContainDownAndUp when interface is up. Set
+            // expectedFinalFlags to flagsForInterfaceUp.
+            expectedFinalFlags = flagsForInterfaceUp;
+            NetdUtils.setInterfaceUp(mNetd, IFACE);
+        } else {
+            // "up" flag will be removed from flagsContainDownAndUp when interface is down. Set
+            // expectedFinalFlags to flagsForInterfaceDown.
+            expectedFinalFlags = flagsForInterfaceDown;
+            NetdUtils.setInterfaceDown(mNetd, IFACE);
+        }
+        verify(mNetd).interfaceSetCfg(
+                argThat(config ->
+                        // Check if actual flags are the same as expected flags.
+                        // TODO: Have a function in MiscAsserts to check if two arrays are the same.
+                        CollectionUtils.all(Arrays.asList(expectedFinalFlags),
+                                flag -> Arrays.asList(config.flags).contains(flag))
+                        && CollectionUtils.all(Arrays.asList(config.flags),
+                                flag -> Arrays.asList(expectedFinalFlags).contains(flag))));
+    }
+
+    @Test
+    public void testSetInterfaceUp() throws Exception {
+        verifyMethodsAndArgumentsOfSetInterface(true /* ifaceUp */);
+    }
+
+    @Test
+    public void testSetInterfaceDown() throws Exception {
+        verifyMethodsAndArgumentsOfSetInterface(false /* ifaceUp */);
+    }
+
+    @Test
+    public void testRemoveAndAddFlags() throws Exception {
+        final String[] flags = new String[] {"flagA", "down", "flagB"};
+        // Add an invalid flag and expect to get an IllegalStateException.
+        assertThrows(IllegalStateException.class,
+                () -> NetdUtils.removeAndAddFlags(flags, "down" /* remove */, "u p" /* add */));
+    }
+}
+