diff --git a/Tethering/src/android/net/ip/IpServer.java b/Tethering/src/android/net/ip/IpServer.java
index 9e0c970..01f5393 100644
--- a/Tethering/src/android/net/ip/IpServer.java
+++ b/Tethering/src/android/net/ip/IpServer.java
@@ -75,6 +75,7 @@
 import com.android.net.module.util.NetdUtils;
 import com.android.net.module.util.SdkUtil.LateSdk;
 import com.android.net.module.util.SharedLog;
+import com.android.net.module.util.SyncStateMachine.StateInfo;
 import com.android.net.module.util.ip.InterfaceController;
 import com.android.net.module.util.ip.IpNeighborMonitor;
 import com.android.net.module.util.ip.IpNeighborMonitor.NeighborEvent;
@@ -87,7 +88,6 @@
 import com.android.networkstack.tethering.util.InterfaceSet;
 import com.android.networkstack.tethering.util.PrefixUtils;
 import com.android.networkstack.tethering.util.StateMachineShim;
-import com.android.networkstack.tethering.util.SyncStateMachine.StateInfo;
 
 import java.net.Inet4Address;
 import java.net.Inet6Address;
diff --git a/Tethering/src/com/android/networkstack/tethering/util/StateMachineShim.java b/Tethering/src/com/android/networkstack/tethering/util/StateMachineShim.java
index 078a35f..c236188 100644
--- a/Tethering/src/com/android/networkstack/tethering/util/StateMachineShim.java
+++ b/Tethering/src/com/android/networkstack/tethering/util/StateMachineShim.java
@@ -22,7 +22,8 @@
 import com.android.internal.annotations.VisibleForTesting;
 import com.android.internal.util.State;
 import com.android.internal.util.StateMachine;
-import com.android.networkstack.tethering.util.SyncStateMachine.StateInfo;
+import com.android.net.module.util.SyncStateMachine;
+import com.android.net.module.util.SyncStateMachine.StateInfo;
 
 import java.util.List;
 
diff --git a/Tethering/tests/unit/src/com/android/networkstack/tethering/util/StateMachineShimTest.kt b/Tethering/tests/unit/src/com/android/networkstack/tethering/util/StateMachineShimTest.kt
index f8e98e3..2417385 100644
--- a/Tethering/tests/unit/src/com/android/networkstack/tethering/util/StateMachineShimTest.kt
+++ b/Tethering/tests/unit/src/com/android/networkstack/tethering/util/StateMachineShimTest.kt
@@ -19,9 +19,10 @@
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import androidx.test.filters.SmallTest
 import com.android.internal.util.State
+import com.android.net.module.util.SyncStateMachine
+import com.android.net.module.util.SyncStateMachine.StateInfo
 import com.android.networkstack.tethering.util.StateMachineShim.AsyncStateMachine
 import com.android.networkstack.tethering.util.StateMachineShim.Dependencies
-import com.android.networkstack.tethering.util.SyncStateMachine.StateInfo
 import kotlin.test.assertFailsWith
 import org.junit.Test
 import org.junit.runner.RunWith
diff --git a/service-t/src/com/android/server/ethernet/EthernetInterfaceStateMachine.java b/service-t/src/com/android/server/ethernet/EthernetInterfaceStateMachine.java
new file mode 100644
index 0000000..b8f6859
--- /dev/null
+++ b/service-t/src/com/android/server/ethernet/EthernetInterfaceStateMachine.java
@@ -0,0 +1,344 @@
+/*
+ * Copyright (C) 2024 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.server.ethernet;
+
+import android.annotation.NonNull;
+import android.annotation.Nullable;
+import android.content.Context;
+import android.net.NetworkCapabilities;
+import android.net.NetworkProvider;
+import android.net.NetworkProvider.NetworkOfferCallback;
+import android.net.NetworkRequest;
+import android.net.NetworkScore;
+import android.net.ip.IIpClient;
+import android.net.ip.IpClientCallbacks;
+import android.net.ip.IpClientManager;
+import android.os.ConditionVariable;
+import android.os.Handler;
+import android.os.Message;
+import android.util.ArraySet;
+import android.util.Log;
+
+import com.android.internal.util.State;
+import com.android.net.module.util.SyncStateMachine;
+import com.android.net.module.util.SyncStateMachine.StateInfo;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Set;
+
+/**
+ * EthernetInterfaceStateMachine manages the lifecycle of an ethernet-like network interface which
+ * includes managing a NetworkOffer, IpClient, and NetworkAgent as well as making the interface
+ * available as a tethering downstream.
+ *
+ * All methods exposed by this class *must* be called on the Handler thread provided in the
+ * constructor.
+ */
+class EthernetInterfaceStateMachine extends SyncStateMachine {
+    private static final String TAG = EthernetInterfaceStateMachine.class.getSimpleName();
+
+    private static final int CMD_ON_LINK_UP          = 1;
+    private static final int CMD_ON_LINK_DOWN        = 2;
+    private static final int CMD_ON_NETWORK_NEEDED   = 3;
+    private static final int CMD_ON_NETWORK_UNNEEDED = 4;
+    private static final int CMD_ON_IPCLIENT_CREATED = 5;
+
+    private class EthernetNetworkOfferCallback implements NetworkOfferCallback {
+        private final Set<Integer> mRequestIds = new ArraySet<>();
+
+        @Override
+        public void onNetworkNeeded(@NonNull NetworkRequest request) {
+            if (this != mNetworkOfferCallback) {
+                return;
+            }
+
+            mRequestIds.add(request.requestId);
+            if (mRequestIds.size() == 1) {
+                processMessage(CMD_ON_NETWORK_NEEDED);
+            }
+        }
+
+        @Override
+        public void onNetworkUnneeded(@NonNull NetworkRequest request) {
+            if (this != mNetworkOfferCallback) {
+                return;
+            }
+
+            if (!mRequestIds.remove(request.requestId)) {
+                // This can only happen if onNetworkNeeded was not called for a request or if
+                // the requestId changed. Both should *never* happen.
+                Log.wtf(TAG, "onNetworkUnneeded called for unknown request");
+            }
+            if (mRequestIds.isEmpty()) {
+                processMessage(CMD_ON_NETWORK_UNNEEDED);
+            }
+        }
+    }
+
+    private class EthernetIpClientCallback extends IpClientCallbacks {
+        private final ConditionVariable mOnQuitCv = new ConditionVariable(false);
+
+        private void safelyPostOnHandler(Runnable r) {
+            mHandler.post(() -> {
+                if (this != mIpClientCallback) {
+                    return;
+                }
+                r.run();
+            });
+        }
+
+        @Override
+        public void onIpClientCreated(IIpClient ipClient) {
+            safelyPostOnHandler(() -> {
+                // TODO: add a SyncStateMachine#processMessage(cmd, obj) overload.
+                processMessage(CMD_ON_IPCLIENT_CREATED, 0, 0,
+                        mDependencies.makeIpClientManager(ipClient));
+            });
+        }
+
+        public void waitOnQuit() {
+            if (!mOnQuitCv.block(5_000 /* timeoutMs */)) {
+                Log.wtf(TAG, "Timed out waiting on IpClient to shutdown.");
+            }
+        }
+
+        @Override
+        public void onQuit() {
+            mOnQuitCv.open();
+        }
+    }
+
+    private @Nullable EthernetNetworkOfferCallback mNetworkOfferCallback;
+    private @Nullable EthernetIpClientCallback mIpClientCallback;
+    private @Nullable IpClientManager mIpClient;
+    private final String mIface;
+    private final Handler mHandler;
+    private final Context mContext;
+    private final NetworkCapabilities mCapabilities;
+    private final NetworkProvider mNetworkProvider;
+    private final EthernetNetworkFactory.Dependencies mDependencies;
+    private boolean mLinkUp = false;
+
+    /** Interface is in tethering mode. */
+    private class TetheringState extends State {
+        @Override
+        public boolean processMessage(Message msg) {
+            switch (msg.what) {
+                case CMD_ON_LINK_UP:
+                case CMD_ON_LINK_DOWN:
+                    // TODO: think about what to do here.
+                    return HANDLED;
+            }
+            return NOT_HANDLED;
+        }
+    }
+
+    /** Link is down */
+    private class LinkDownState extends State {
+        @Override
+        public boolean processMessage(Message msg) {
+            switch (msg.what) {
+                case CMD_ON_LINK_UP:
+                    transitionTo(mStoppedState);
+                    return HANDLED;
+                case CMD_ON_LINK_DOWN:
+                    // do nothing, already in the correct state.
+                    return HANDLED;
+            }
+            return NOT_HANDLED;
+        }
+    }
+
+    /** Parent states of all states that do not cause a NetworkOffer to be extended. */
+    private class NetworkOfferExtendedState extends State {
+        @Override
+        public void enter() {
+            if (mNetworkOfferCallback != null) {
+                // This should never happen. If it happens anyway, log and move on.
+                Log.wtf(TAG, "Previous NetworkOffer was never retracted");
+            }
+
+            mNetworkOfferCallback = new EthernetNetworkOfferCallback();
+            final NetworkScore defaultScore = new NetworkScore.Builder().build();
+            mNetworkProvider.registerNetworkOffer(defaultScore,
+                    new NetworkCapabilities(mCapabilities), cmd -> mHandler.post(cmd),
+                    mNetworkOfferCallback);
+        }
+
+        @Override
+        public boolean processMessage(Message msg) {
+            switch (msg.what) {
+                case CMD_ON_LINK_UP:
+                    // do nothing, already in the correct state.
+                    return HANDLED;
+                case CMD_ON_LINK_DOWN:
+                    transitionTo(mLinkDownState);
+                    return HANDLED;
+            }
+            return NOT_HANDLED;
+        }
+
+        @Override
+        public void exit() {
+            mNetworkProvider.unregisterNetworkOffer(mNetworkOfferCallback);
+            mNetworkOfferCallback = null;
+        }
+    }
+
+    /**
+     * Offer is extended but has not been requested.
+     *
+     * StoppedState's sole purpose is to react to a CMD_ON_NETWORK_NEEDED and transition to
+     * StartedState when that happens. Note that StoppedState could be rolled into
+     * NetworkOfferExtendedState. However, keeping the states separate provides some additional
+     * protection by logging a Log.wtf if a CMD_ON_NETWORK_NEEDED is received in an unexpected state
+     * (i.e. StartedState or RunningState). StoppedState is a child of NetworkOfferExtendedState.
+     */
+    private class StoppedState extends State {
+        @Override
+        public boolean processMessage(Message msg) {
+            switch (msg.what) {
+                case CMD_ON_NETWORK_NEEDED:
+                    transitionTo(mStartedState);
+                    return HANDLED;
+            }
+            return NOT_HANDLED;
+        }
+    }
+
+    /** Network is needed, starts IpClient and manages its lifecycle */
+    private class StartedState extends State {
+        @Override
+        public void enter() {
+            mIpClientCallback = new EthernetIpClientCallback();
+            mDependencies.makeIpClient(mContext, mIface, mIpClientCallback);
+        }
+
+        @Override
+        public boolean processMessage(Message msg) {
+            switch (msg.what) {
+                case CMD_ON_NETWORK_UNNEEDED:
+                    transitionTo(mStoppedState);
+                    return HANDLED;
+                case CMD_ON_IPCLIENT_CREATED:
+                    mIpClient = (IpClientManager) msg.obj;
+                    transitionTo(mRunningState);
+                    return HANDLED;
+            }
+            return NOT_HANDLED;
+        }
+
+        @Override
+        public void exit() {
+            if (mIpClient != null) {
+                mIpClient.shutdown();
+                // TODO: consider adding a StoppingState and making the shutdown operation
+                // asynchronous.
+                mIpClientCallback.waitOnQuit();
+            }
+            mIpClientCallback = null;
+        }
+    }
+
+    /** IpClient is running, starts provisioning and registers NetworkAgent */
+    private class RunningState extends State {
+
+    }
+
+    private final TetheringState mTetheringState = new TetheringState();
+    private final LinkDownState mLinkDownState = new LinkDownState();
+    private final NetworkOfferExtendedState mOfferExtendedState = new NetworkOfferExtendedState();
+    private final StoppedState mStoppedState = new StoppedState();
+    private final StartedState mStartedState = new StartedState();
+    private final RunningState mRunningState = new RunningState();
+
+    public EthernetInterfaceStateMachine(String iface, Handler handler, Context context,
+            NetworkCapabilities capabilities, NetworkProvider provider,
+            EthernetNetworkFactory.Dependencies deps) {
+        super(TAG + "." + iface, handler.getLooper().getThread());
+
+        mIface = iface;
+        mHandler = handler;
+        mContext = context;
+        mCapabilities = capabilities;
+        mNetworkProvider = provider;
+        mDependencies = deps;
+
+        // Interface lifecycle:
+        //           [ LinkDownState ]
+        //                   |
+        //                   v
+        //             *link comes up*
+        //                   |
+        //                   v
+        //            [ StoppedState ]
+        //                   |
+        //                   v
+        //           *network is needed*
+        //                   |
+        //                   v
+        //            [ StartedState ]
+        //                   |
+        //                   v
+        //           *IpClient is created*
+        //                   |
+        //                   v
+        //            [ RunningState ]
+        //                   |
+        //                   v
+        //  *interface is requested for tethering*
+        //                   |
+        //                   v
+        //            [TetheringState]
+        //
+        // Tethering mode is special as the interface is configured by Tethering, rather than the
+        // ethernet module.
+        final List<StateInfo> states = new ArrayList<>();
+        states.add(new StateInfo(mTetheringState, null));
+
+        // CHECKSTYLE:OFF IndentationCheck
+        // Initial state
+        states.add(new StateInfo(mLinkDownState, null));
+        states.add(new StateInfo(mOfferExtendedState, null));
+            states.add(new StateInfo(mStoppedState, mOfferExtendedState));
+            states.add(new StateInfo(mStartedState, mOfferExtendedState));
+                states.add(new StateInfo(mRunningState, mStartedState));
+        // CHECKSTYLE:ON IndentationCheck
+        addAllStates(states);
+
+        // TODO: set initial state to TetheringState if a tethering interface has been requested and
+        // this is the first interface to be added.
+        start(mLinkDownState);
+    }
+
+    public boolean updateLinkState(boolean up) {
+        if (mLinkUp == up) {
+            return false;
+        }
+
+        // TODO: consider setting mLinkUp as part of processMessage().
+        mLinkUp = up;
+        if (!up) { // was up, goes down
+            processMessage(CMD_ON_LINK_DOWN);
+        } else { // was down, comes up
+            processMessage(CMD_ON_LINK_UP);
+        }
+
+        return true;
+    }
+}
diff --git a/staticlibs/Android.bp b/staticlibs/Android.bp
index e2834b0..71f388d 100644
--- a/staticlibs/Android.bp
+++ b/staticlibs/Android.bp
@@ -39,12 +39,13 @@
         "device/com/android/net/module/util/DeviceConfigUtils.java",
         "device/com/android/net/module/util/DomainUtils.java",
         "device/com/android/net/module/util/FdEventsReader.java",
+        "device/com/android/net/module/util/FeatureVersions.java",
+        "device/com/android/net/module/util/HandlerUtils.java",
         "device/com/android/net/module/util/NetworkMonitorUtils.java",
         "device/com/android/net/module/util/PacketReader.java",
         "device/com/android/net/module/util/SharedLog.java",
         "device/com/android/net/module/util/SocketUtils.java",
-        "device/com/android/net/module/util/FeatureVersions.java",
-        "device/com/android/net/module/util/HandlerUtils.java",
+        "device/com/android/net/module/util/SyncStateMachine.java",
         // This library is used by system modules, for which the system health impact of Kotlin
         // has not yet been evaluated. Annotations may need jarjar'ing.
         // "src_devicecommon/**/*.kt",
@@ -68,6 +69,7 @@
         "//packages/modules/CaptivePortalLogin",
     ],
     static_libs: [
+        "modules-utils-statemachine",
         "net-utils-framework-common",
     ],
     libs: [
diff --git a/Tethering/src/com/android/networkstack/tethering/util/SyncStateMachine.java b/staticlibs/device/com/android/net/module/util/SyncStateMachine.java
similarity index 96%
rename from Tethering/src/com/android/networkstack/tethering/util/SyncStateMachine.java
rename to staticlibs/device/com/android/net/module/util/SyncStateMachine.java
index a17eb26..da184d3 100644
--- a/Tethering/src/com/android/networkstack/tethering/util/SyncStateMachine.java
+++ b/staticlibs/device/com/android/net/module/util/SyncStateMachine.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package com.android.networkstack.tethering.util;
+package com.android.net.module.util;
 
 import android.annotation.NonNull;
 import android.annotation.Nullable;
@@ -165,6 +165,11 @@
      * The message is processed sequentially, so calling this method recursively is not permitted.
      * In other words, using this method inside State#enter, State#exit, or State#processMessage
      * is incorrect and will result in an IllegalStateException.
+     *
+     * @param what is assigned to Message.what
+     * @param arg1 is assigned to Message.arg1
+     * @param arg2 is assigned to Message.arg2
+     * @param obj  is assigned to Message.obj
      */
     public final void processMessage(int what, int arg1, int arg2, @Nullable Object obj) {
         ensureCorrectThread();
@@ -189,6 +194,15 @@
         mCurrentlyProcessing = Integer.MIN_VALUE;
     }
 
+    /**
+     * Synchronously process a message and perform state transition.
+     *
+     * @param what is assigned to Message.what.
+     */
+    public final void processMessage(int what) {
+        processMessage(what, 0, 0, null);
+    }
+
     private void maybeProcessSelfMessageQueue() {
         while (!mSelfMsgQueue.isEmpty()) {
             currentStateProcessMessageThenPerformTransitions(mSelfMsgQueue.poll());
diff --git a/Tethering/tests/unit/src/com/android/networkstack/tethering/util/SyncStateMachineTest.kt b/staticlibs/tests/unit/src/com/android/net/module/util/SyncStateMachineTest.kt
similarity index 98%
rename from Tethering/tests/unit/src/com/android/networkstack/tethering/util/SyncStateMachineTest.kt
rename to staticlibs/tests/unit/src/com/android/net/module/util/SyncStateMachineTest.kt
index 3a57fdd..d534054 100644
--- a/Tethering/tests/unit/src/com/android/networkstack/tethering/util/SyncStateMachineTest.kt
+++ b/staticlibs/tests/unit/src/com/android/net/module/util/SyncStateMachineTest.kt
@@ -13,13 +13,13 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package com.android.networkstack.tethering.util
+package com.android.net.module.util
 
 import android.os.Message
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import androidx.test.filters.SmallTest
 import com.android.internal.util.State
-import com.android.networkstack.tethering.util.SyncStateMachine.StateInfo
+import com.android.net.module.util.SyncStateMachine.StateInfo
 import java.util.ArrayDeque
 import java.util.ArrayList
 import kotlin.test.assertFailsWith
@@ -45,7 +45,7 @@
 
 @RunWith(AndroidJUnit4::class)
 @SmallTest
-class SynStateMachineTest {
+class SyncStateMachineTest {
     private val mState1 = spy(object : TestState(MSG_1) {})
     private val mState2 = spy(object : TestState(MSG_2) {})
     private val mState3 = spy(object : TestState(MSG_3) {})
diff --git a/tests/unit/java/com/android/server/ethernet/EthernetInterfaceStateMachineTest.kt b/tests/unit/java/com/android/server/ethernet/EthernetInterfaceStateMachineTest.kt
new file mode 100644
index 0000000..c8b2f65
--- /dev/null
+++ b/tests/unit/java/com/android/server/ethernet/EthernetInterfaceStateMachineTest.kt
@@ -0,0 +1,87 @@
+/*
+ * Copyright (C) 2024 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.
+ */
+// ktlint does not allow annotating function argument literals inline. Disable the specific rule
+// since this negatively affects readability.
+@file:Suppress("ktlint:standard:comment-wrapping")
+
+package com.android.server.ethernet
+
+import android.content.Context
+import android.net.NetworkCapabilities
+import android.net.NetworkProvider
+import android.net.NetworkProvider.NetworkOfferCallback
+import android.os.Build
+import android.os.Handler
+import android.os.test.TestLooper
+import androidx.test.filters.SmallTest
+import com.android.testutils.DevSdkIgnoreRule
+import com.android.testutils.DevSdkIgnoreRunner
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.mockito.ArgumentCaptor
+import org.mockito.ArgumentMatchers.any
+import org.mockito.ArgumentMatchers.eq
+import org.mockito.Mock
+import org.mockito.Mockito.inOrder
+import org.mockito.Mockito.verify
+import org.mockito.MockitoAnnotations
+
+private const val IFACE = "eth0"
+private val CAPS = NetworkCapabilities.Builder().build()
+
+@SmallTest
+@RunWith(DevSdkIgnoreRunner::class)
+@DevSdkIgnoreRule.IgnoreUpTo(Build.VERSION_CODES.S_V2)
+class EthernetInterfaceStateMachineTest {
+    private lateinit var looper: TestLooper
+    private lateinit var handler: Handler
+    private lateinit var ifaceState: EthernetInterfaceStateMachine
+
+    @Mock private lateinit var context: Context
+    @Mock private lateinit var provider: NetworkProvider
+    @Mock private lateinit var deps: EthernetNetworkFactory.Dependencies
+
+    // There seems to be no (obvious) way to force execution of @Before and @Test annotation on the
+    // same thread. Since SyncStateMachine requires all interactions to be called from the same
+    // thread that is provided at construction time (in this case, the thread that TestLooper() is
+    // called on), setUp() must be called directly from the @Test method.
+    // TODO: find a way to fix this in the test runner.
+    fun setUp() {
+        looper = TestLooper()
+        handler = Handler(looper.looper)
+        MockitoAnnotations.initMocks(this)
+
+        ifaceState = EthernetInterfaceStateMachine(IFACE, handler, context, CAPS, provider, deps)
+    }
+
+    @Test
+    fun testUpdateLinkState_networkOfferRegisteredAndRetracted() {
+        setUp()
+
+        ifaceState.updateLinkState(/* up= */ true)
+
+        // link comes up: validate the NetworkOffer is registered and capture callback object.
+        val inOrder = inOrder(provider)
+        val networkOfferCb = ArgumentCaptor.forClass(NetworkOfferCallback::class.java).also {
+            inOrder.verify(provider).registerNetworkOffer(any(), any(), any(), it.capture())
+        }.value
+
+        ifaceState.updateLinkState(/* up */ false)
+
+        // link goes down: validate the NetworkOffer is retracted
+        inOrder.verify(provider).unregisterNetworkOffer(eq(networkOfferCb))
+    }
+}