diff --git a/common/moduleutils/Android.bp b/common/moduleutils/Android.bp
index 4b2a4b8..d0dd584 100644
--- a/common/moduleutils/Android.bp
+++ b/common/moduleutils/Android.bp
@@ -51,10 +51,14 @@
     name: "tethering-module-utils-srcs",
     srcs: [
         "src/android/net/ip/InterfaceController.java",
+        "src/android/net/ip/IpNeighborMonitor.java",
         "src/android/net/netlink/*.java",
         "src/android/net/shared/NetdUtils.java",
         "src/android/net/shared/RouteUtils.java",
+        "src/android/net/util/FdEventsReader.java",
         "src/android/net/util/InterfaceParams.java",
+        "src/android/net/util/PacketReader.java",
         "src/android/net/util/SharedLog.java"
     ],
+    visibility: ["//frameworks/base/packages/Tethering"],
 }
diff --git a/common/moduleutils/src/android/net/ip/IpNeighborMonitor.java b/common/moduleutils/src/android/net/ip/IpNeighborMonitor.java
new file mode 100644
index 0000000..d6706d4
--- /dev/null
+++ b/common/moduleutils/src/android/net/ip/IpNeighborMonitor.java
@@ -0,0 +1,250 @@
+/*
+ * Copyright (C) 2017 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 android.net.ip;
+
+import static android.net.netlink.NetlinkConstants.RTM_DELNEIGH;
+import static android.net.netlink.NetlinkConstants.hexify;
+import static android.net.netlink.NetlinkConstants.stringForNlMsgType;
+import static android.net.util.SocketUtils.makeNetlinkSocketAddress;
+import static android.system.OsConstants.AF_NETLINK;
+import static android.system.OsConstants.NETLINK_ROUTE;
+import static android.system.OsConstants.SOCK_DGRAM;
+import static android.system.OsConstants.SOCK_NONBLOCK;
+
+import android.net.MacAddress;
+import android.net.netlink.NetlinkErrorMessage;
+import android.net.netlink.NetlinkMessage;
+import android.net.netlink.NetlinkSocket;
+import android.net.netlink.RtNetlinkNeighborMessage;
+import android.net.netlink.StructNdMsg;
+import android.net.util.PacketReader;
+import android.net.util.SharedLog;
+import android.net.util.SocketUtils;
+import android.os.Handler;
+import android.os.SystemClock;
+import android.system.ErrnoException;
+import android.system.Os;
+import android.system.OsConstants;
+import android.util.Log;
+
+import java.io.FileDescriptor;
+import java.io.IOException;
+import java.net.InetAddress;
+import java.net.SocketAddress;
+import java.net.SocketException;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.util.StringJoiner;
+
+
+/**
+ * IpNeighborMonitor.
+ *
+ * Monitors the kernel rtnetlink neighbor notifications and presents to callers
+ * NeighborEvents describing each event. Callers can provide a consumer instance
+ * to both filter (e.g. by interface index and IP address) and handle the
+ * generated NeighborEvents.
+ *
+ * @hide
+ */
+public class IpNeighborMonitor extends PacketReader {
+    private static final String TAG = IpNeighborMonitor.class.getSimpleName();
+    private static final boolean DBG = false;
+    private static final boolean VDBG = false;
+
+    /**
+     * Make the kernel perform neighbor reachability detection (IPv4 ARP or IPv6 ND)
+     * for the given IP address on the specified interface index.
+     *
+     * @return 0 if the request was successfully passed to the kernel; otherwise return
+     *         a non-zero error code.
+     */
+    public static int startKernelNeighborProbe(int ifIndex, InetAddress ip) {
+        final String msgSnippet = "probing ip=" + ip.getHostAddress() + "%" + ifIndex;
+        if (DBG) { Log.d(TAG, msgSnippet); }
+
+        final byte[] msg = RtNetlinkNeighborMessage.newNewNeighborMessage(
+                1, ip, StructNdMsg.NUD_PROBE, ifIndex, null);
+
+        try {
+            NetlinkSocket.sendOneShotKernelMessage(NETLINK_ROUTE, msg);
+        } catch (ErrnoException e) {
+            Log.e(TAG, "Error " + msgSnippet + ": " + e);
+            return -e.errno;
+        }
+
+        return 0;
+    }
+
+    public static class NeighborEvent {
+        final long elapsedMs;
+        final short msgType;
+        final int ifindex;
+        final InetAddress ip;
+        final short nudState;
+        final MacAddress macAddr;
+
+        public NeighborEvent(long elapsedMs, short msgType, int ifindex, InetAddress ip,
+                short nudState, MacAddress macAddr) {
+            this.elapsedMs = elapsedMs;
+            this.msgType = msgType;
+            this.ifindex = ifindex;
+            this.ip = ip;
+            this.nudState = nudState;
+            this.macAddr = macAddr;
+        }
+
+        boolean isConnected() {
+            return (msgType != RTM_DELNEIGH) && StructNdMsg.isNudStateConnected(nudState);
+        }
+
+        boolean isValid() {
+            return (msgType != RTM_DELNEIGH) && StructNdMsg.isNudStateValid(nudState);
+        }
+
+        @Override
+        public String toString() {
+            final StringJoiner j = new StringJoiner(",", "NeighborEvent{", "}");
+            return j.add("@" + elapsedMs)
+                    .add(stringForNlMsgType(msgType))
+                    .add("if=" + ifindex)
+                    .add(ip.getHostAddress())
+                    .add(StructNdMsg.stringForNudState(nudState))
+                    .add("[" + macAddr + "]")
+                    .toString();
+        }
+    }
+
+    // TODO: move NetworkStackUtils.closeSocketQuietly to somewhere accessible to this file.
+    private void closeSocketQuietly(FileDescriptor fd) {
+        try {
+            SocketUtils.closeSocket(fd);
+        } catch (IOException ignored) {
+        }
+    }
+
+    public interface NeighborEventConsumer {
+        // Every neighbor event received on the netlink socket is passed in
+        // here. Subclasses should filter for events of interest.
+        public void accept(NeighborEvent event);
+    }
+
+    private final SharedLog mLog;
+    private final NeighborEventConsumer mConsumer;
+
+    public IpNeighborMonitor(Handler h, SharedLog log, NeighborEventConsumer cb) {
+        super(h, NetlinkSocket.DEFAULT_RECV_BUFSIZE);
+        mLog = log.forSubComponent(TAG);
+        mConsumer = (cb != null) ? cb : (event) -> { /* discard */ };
+    }
+
+    @Override
+    protected FileDescriptor createFd() {
+        FileDescriptor fd = null;
+
+        try {
+            fd = Os.socket(AF_NETLINK, SOCK_DGRAM | SOCK_NONBLOCK, NETLINK_ROUTE);
+            Os.bind(fd, makeNetlinkSocketAddress(0, OsConstants.RTMGRP_NEIGH));
+            NetlinkSocket.connectToKernel(fd);
+
+            if (VDBG) {
+                final SocketAddress nlAddr = Os.getsockname(fd);
+                Log.d(TAG, "bound to sockaddr_nl{" + nlAddr.toString() + "}");
+            }
+        } catch (ErrnoException|SocketException e) {
+            logError("Failed to create rtnetlink socket", e);
+            closeSocketQuietly(fd);
+            return null;
+        }
+
+        return fd;
+    }
+
+    @Override
+    protected void handlePacket(byte[] recvbuf, int length) {
+        final long whenMs = SystemClock.elapsedRealtime();
+
+        final ByteBuffer byteBuffer = ByteBuffer.wrap(recvbuf, 0, length);
+        byteBuffer.order(ByteOrder.nativeOrder());
+
+        parseNetlinkMessageBuffer(byteBuffer, whenMs);
+    }
+
+    private void parseNetlinkMessageBuffer(ByteBuffer byteBuffer, long whenMs) {
+        while (byteBuffer.remaining() > 0) {
+            final int position = byteBuffer.position();
+            final NetlinkMessage nlMsg = NetlinkMessage.parse(byteBuffer);
+            if (nlMsg == null || nlMsg.getHeader() == null) {
+                byteBuffer.position(position);
+                mLog.e("unparsable netlink msg: " + hexify(byteBuffer));
+                break;
+            }
+
+            if (nlMsg instanceof NetlinkErrorMessage) {
+                mLog.e("netlink error: " + nlMsg);
+                continue;
+            } else if (!(nlMsg instanceof RtNetlinkNeighborMessage)) {
+                mLog.i("non-rtnetlink neighbor msg: " + nlMsg);
+                continue;
+            }
+
+            evaluateRtNetlinkNeighborMessage((RtNetlinkNeighborMessage) nlMsg, whenMs);
+        }
+    }
+
+    private void evaluateRtNetlinkNeighborMessage(
+            RtNetlinkNeighborMessage neighMsg, long whenMs) {
+        final short msgType = neighMsg.getHeader().nlmsg_type;
+        final StructNdMsg ndMsg = neighMsg.getNdHeader();
+        if (ndMsg == null) {
+            mLog.e("RtNetlinkNeighborMessage without ND message header!");
+            return;
+        }
+
+        final int ifindex = ndMsg.ndm_ifindex;
+        final InetAddress destination = neighMsg.getDestination();
+        final short nudState =
+                (msgType == RTM_DELNEIGH)
+                ? StructNdMsg.NUD_NONE
+                : ndMsg.ndm_state;
+
+        final NeighborEvent event = new NeighborEvent(
+                whenMs, msgType, ifindex, destination, nudState,
+                getMacAddress(neighMsg.getLinkLayerAddress()));
+
+        if (VDBG) {
+            Log.d(TAG, neighMsg.toString());
+        }
+        if (DBG) {
+            Log.d(TAG, event.toString());
+        }
+
+        mConsumer.accept(event);
+    }
+
+    private static MacAddress getMacAddress(byte[] linkLayerAddress) {
+        if (linkLayerAddress != null) {
+            try {
+                return MacAddress.fromBytes(linkLayerAddress);
+            } catch (IllegalArgumentException e) {
+                Log.e(TAG, "Failed to parse link-layer address: " + hexify(linkLayerAddress));
+            }
+        }
+
+        return null;
+    }
+}
diff --git a/common/moduleutils/src/android/net/util/FdEventsReader.java b/common/moduleutils/src/android/net/util/FdEventsReader.java
new file mode 100644
index 0000000..5a1154f
--- /dev/null
+++ b/common/moduleutils/src/android/net/util/FdEventsReader.java
@@ -0,0 +1,259 @@
+/*
+ * Copyright (C) 2016 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 android.net.util;
+
+import static android.os.MessageQueue.OnFileDescriptorEventListener.EVENT_ERROR;
+import static android.os.MessageQueue.OnFileDescriptorEventListener.EVENT_INPUT;
+
+import android.os.Handler;
+import android.os.Looper;
+import android.os.MessageQueue;
+import android.system.ErrnoException;
+import android.system.OsConstants;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+import java.io.FileDescriptor;
+import java.io.IOException;
+
+
+/**
+ * This class encapsulates the mechanics of registering a file descriptor
+ * with a thread's Looper and handling read events (and errors).
+ *
+ * Subclasses MUST implement createFd() and SHOULD override handlePacket(). They MAY override
+ * onStop() and onStart().
+ *
+ * Subclasses can expect a call life-cycle like the following:
+ *
+ *     [1] when a client calls start(), createFd() is called, followed by the onStart() hook if all
+ *         goes well. Implementations may override onStart() for additional initialization.
+ *
+ *     [2] yield, waiting for read event or error notification:
+ *
+ *             [a] readPacket() && handlePacket()
+ *
+ *             [b] if (no error):
+ *                     goto 2
+ *                 else:
+ *                     goto 3
+ *
+ *     [3] when a client calls stop(), the onStop() hook is called (unless already stopped or never
+ *         started). Implementations may override onStop() for additional cleanup.
+ *
+ * The packet receive buffer is recycled on every read call, so subclasses
+ * should make any copies they would like inside their handlePacket()
+ * implementation.
+ *
+ * All public methods MUST only be called from the same thread with which
+ * the Handler constructor argument is associated.
+ *
+ * @param <BufferType> the type of the buffer used to read data.
+ */
+public abstract class FdEventsReader<BufferType> {
+    private static final int FD_EVENTS = EVENT_INPUT | EVENT_ERROR;
+    private static final int UNREGISTER_THIS_FD = 0;
+
+    @NonNull
+    private final Handler mHandler;
+    @NonNull
+    private final MessageQueue mQueue;
+    @NonNull
+    private final BufferType mBuffer;
+    @Nullable
+    private FileDescriptor mFd;
+    private long mPacketsReceived;
+
+    protected static void closeFd(FileDescriptor fd) {
+        try {
+            SocketUtils.closeSocket(fd);
+        } catch (IOException ignored) {
+        }
+    }
+
+    protected FdEventsReader(@NonNull Handler h, @NonNull BufferType buffer) {
+        mHandler = h;
+        mQueue = mHandler.getLooper().getQueue();
+        mBuffer = buffer;
+    }
+
+    /** Start this FdEventsReader. */
+    public boolean start() {
+        if (!onCorrectThread()) {
+            throw new IllegalStateException("start() called from off-thread");
+        }
+
+        return createAndRegisterFd();
+    }
+
+    /** Stop this FdEventsReader and destroy the file descriptor. */
+    public void stop() {
+        if (!onCorrectThread()) {
+            throw new IllegalStateException("stop() called from off-thread");
+        }
+
+        unregisterAndDestroyFd();
+    }
+
+    @NonNull
+    public Handler getHandler() {
+        return mHandler;
+    }
+
+    protected abstract int recvBufSize(@NonNull BufferType buffer);
+
+    /** Returns the size of the receive buffer. */
+    public int recvBufSize() {
+        return recvBufSize(mBuffer);
+    }
+
+    /**
+     * Get the number of successful calls to {@link #readPacket(FileDescriptor, Object)}.
+     *
+     * <p>A call was successful if {@link #readPacket(FileDescriptor, Object)} returned a value > 0.
+     */
+    public final long numPacketsReceived() {
+        return mPacketsReceived;
+    }
+
+    /**
+     * Subclasses MUST create the listening socket here, including setting all desired socket
+     * options, interface or address/port binding, etc. The socket MUST be created nonblocking.
+     */
+    @Nullable
+    protected abstract FileDescriptor createFd();
+
+    /**
+     * Implementations MUST return the bytes read or throw an Exception.
+     *
+     * <p>The caller may throw a {@link ErrnoException} with {@link OsConstants#EAGAIN} or
+     * {@link OsConstants#EINTR}, in which case {@link FdEventsReader} will ignore the buffer
+     * contents and respectively wait for further input or retry the read immediately. For all other
+     * exceptions, the {@link FdEventsReader} will be stopped with no more interactions with this
+     * method.
+     */
+    protected abstract int readPacket(@NonNull FileDescriptor fd, @NonNull BufferType buffer)
+            throws Exception;
+
+    /**
+     * Called by the main loop for every packet.  Any desired copies of
+     * |recvbuf| should be made in here, as the underlying byte array is
+     * reused across all reads.
+     */
+    protected void handlePacket(@NonNull BufferType recvbuf, int length) {}
+
+    /**
+     * Called by the main loop to log errors.  In some cases |e| may be null.
+     */
+    protected void logError(@NonNull String msg, @Nullable Exception e) {}
+
+    /**
+     * Called by start(), if successful, just prior to returning.
+     */
+    protected void onStart() {}
+
+    /**
+     * Called by stop() just prior to returning.
+     */
+    protected void onStop() {}
+
+    private boolean createAndRegisterFd() {
+        if (mFd != null) return true;
+
+        try {
+            mFd = createFd();
+        } catch (Exception e) {
+            logError("Failed to create socket: ", e);
+            closeFd(mFd);
+            mFd = null;
+        }
+
+        if (mFd == null) return false;
+
+        mQueue.addOnFileDescriptorEventListener(
+                mFd,
+                FD_EVENTS,
+                (fd, events) -> {
+                    // Always call handleInput() so read/recvfrom are given
+                    // a proper chance to encounter a meaningful errno and
+                    // perhaps log a useful error message.
+                    if (!isRunning() || !handleInput()) {
+                        unregisterAndDestroyFd();
+                        return UNREGISTER_THIS_FD;
+                    }
+                    return FD_EVENTS;
+                });
+        onStart();
+        return true;
+    }
+
+    private boolean isRunning() {
+        return (mFd != null) && mFd.valid();
+    }
+
+    // Keep trying to read until we get EAGAIN/EWOULDBLOCK or some fatal error.
+    private boolean handleInput() {
+        while (isRunning()) {
+            final int bytesRead;
+
+            try {
+                bytesRead = readPacket(mFd, mBuffer);
+                if (bytesRead < 1) {
+                    if (isRunning()) logError("Socket closed, exiting", null);
+                    break;
+                }
+                mPacketsReceived++;
+            } catch (ErrnoException e) {
+                if (e.errno == OsConstants.EAGAIN) {
+                    // We've read everything there is to read this time around.
+                    return true;
+                } else if (e.errno == OsConstants.EINTR) {
+                    continue;
+                } else {
+                    if (isRunning()) logError("readPacket error: ", e);
+                    break;
+                }
+            } catch (Exception e) {
+                if (isRunning()) logError("readPacket error: ", e);
+                break;
+            }
+
+            try {
+                handlePacket(mBuffer, bytesRead);
+            } catch (Exception e) {
+                logError("handlePacket error: ", e);
+                break;
+            }
+        }
+
+        return false;
+    }
+
+    private void unregisterAndDestroyFd() {
+        if (mFd == null) return;
+
+        mQueue.removeOnFileDescriptorEventListener(mFd);
+        closeFd(mFd);
+        mFd = null;
+        onStop();
+    }
+
+    private boolean onCorrectThread() {
+        return (mHandler.getLooper() == Looper.myLooper());
+    }
+}
diff --git a/common/moduleutils/src/android/net/util/PacketReader.java b/common/moduleutils/src/android/net/util/PacketReader.java
new file mode 100644
index 0000000..0be7187
--- /dev/null
+++ b/common/moduleutils/src/android/net/util/PacketReader.java
@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2018 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 android.net.util;
+
+import static java.lang.Math.max;
+
+import android.os.Handler;
+import android.system.Os;
+
+import java.io.FileDescriptor;
+
+/**
+ * Specialization of {@link FdEventsReader} that reads packets into a byte array.
+ *
+ * TODO: rename this class to something more correctly descriptive (something
+ * like [or less horrible than] FdReadEventsHandler?).
+ */
+public abstract class PacketReader extends FdEventsReader<byte[]> {
+
+    public static final int DEFAULT_RECV_BUF_SIZE = 2 * 1024;
+
+    protected PacketReader(Handler h) {
+        this(h, DEFAULT_RECV_BUF_SIZE);
+    }
+
+    protected PacketReader(Handler h, int recvBufSize) {
+        super(h, new byte[max(recvBufSize, DEFAULT_RECV_BUF_SIZE)]);
+    }
+
+    @Override
+    protected final int recvBufSize(byte[] buffer) {
+        return buffer.length;
+    }
+
+    /**
+     * Subclasses MAY override this to change the default read() implementation
+     * in favour of, say, recvfrom().
+     *
+     * Implementations MUST return the bytes read or throw an Exception.
+     */
+    @Override
+    protected int readPacket(FileDescriptor fd, byte[] packetBuffer) throws Exception {
+        return Os.read(fd, packetBuffer, 0, packetBuffer.length);
+    }
+}