diff --git a/core/java/android/net/SocketKeepalive.java b/core/java/android/net/SocketKeepalive.java
index 9d91620..46eddde 100644
--- a/core/java/android/net/SocketKeepalive.java
+++ b/core/java/android/net/SocketKeepalive.java
@@ -43,6 +43,10 @@
  * To stop an existing keepalive, call {@link SocketKeepalive#stop}. The system will call
  * {@link SocketKeepalive.Callback#onStopped} if the operation was successful or
  * {@link SocketKeepalive.Callback#onError} if an error occurred.
+ *
+ * The device SHOULD support keepalive offload. If it does not, it MUST reply with
+ * {@link SocketKeepalive.Callback#onError} with {@code ERROR_UNSUPPORTED} to any keepalive offload
+ * request. If it does, it MUST support at least 3 concurrent keepalive slots per transport.
  */
 public abstract class SocketKeepalive implements AutoCloseable {
     static final String TAG = "SocketKeepalive";
diff --git a/core/java/android/net/util/KeepaliveUtils.java b/core/java/android/net/util/KeepaliveUtils.java
new file mode 100644
index 0000000..569fed1
--- /dev/null
+++ b/core/java/android/net/util/KeepaliveUtils.java
@@ -0,0 +1,121 @@
+/*
+ * Copyright (C) 2019 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 android.annotation.NonNull;
+import android.content.Context;
+import android.content.res.Resources;
+import android.net.NetworkCapabilities;
+import android.text.TextUtils;
+import android.util.AndroidRuntimeException;
+
+import com.android.internal.R;
+
+/**
+ * Collection of utilities for socket keepalive offload.
+ *
+ * @hide
+ */
+public final class KeepaliveUtils {
+
+    public static final String TAG = "KeepaliveUtils";
+
+    // Minimum supported keepalive count per transport if the network supports keepalive.
+    public static final int MIN_SUPPORTED_KEEPALIVE_COUNT = 3;
+
+    public static class KeepaliveDeviceConfigurationException extends AndroidRuntimeException {
+        public KeepaliveDeviceConfigurationException(final String msg) {
+            super(msg);
+        }
+    }
+
+    /**
+     * Read supported keepalive count for each transport type from overlay resource. This should be
+     * used to create a local variable store of resource customization, and use it as the input for
+     * {@link getSupportedKeepalivesForNetworkCapabilities}.
+     *
+     * @param context The context to read resource from.
+     * @return An array of supported keepalive count for each transport type.
+     */
+    @NonNull
+    public static int[] getSupportedKeepalives(@NonNull Context context) {
+        String[] res = null;
+        try {
+            res = context.getResources().getStringArray(
+                    R.array.config_networkSupportedKeepaliveCount);
+        } catch (Resources.NotFoundException unused) {
+        }
+        if (res == null) throw new KeepaliveDeviceConfigurationException("invalid resource");
+
+        final int[] ret = new int[NetworkCapabilities.MAX_TRANSPORT + 1];
+        for (final String row : res) {
+            if (TextUtils.isEmpty(row)) {
+                throw new KeepaliveDeviceConfigurationException("Empty string");
+            }
+            final String[] arr = row.split(",");
+            if (arr.length != 2) {
+                throw new KeepaliveDeviceConfigurationException("Invalid parameter length");
+            }
+
+            int transport;
+            int supported;
+            try {
+                transport = Integer.parseInt(arr[0]);
+                supported = Integer.parseInt(arr[1]);
+            } catch (NumberFormatException e) {
+                throw new KeepaliveDeviceConfigurationException("Invalid number format");
+            }
+
+            if (!NetworkCapabilities.isValidTransport(transport)) {
+                throw new KeepaliveDeviceConfigurationException("Invalid transport " + transport);
+            }
+
+            // Customized values should be either 0 to indicate the network doesn't support
+            // keepalive offload, or a positive value that is at least
+            // MIN_SUPPORTED_KEEPALIVE_COUNT if supported.
+            if (supported != 0 && supported < MIN_SUPPORTED_KEEPALIVE_COUNT) {
+                throw new KeepaliveDeviceConfigurationException(
+                        "Invalid supported count " + supported + " for "
+                                + NetworkCapabilities.transportNameOf(transport));
+            }
+            ret[transport] = supported;
+        }
+        return ret;
+    }
+
+    /**
+     * Get supported keepalive count for the given {@link NetworkCapabilities}.
+     *
+     * @param supportedKeepalives An array of supported keepalive count for each transport type.
+     * @param nc The {@link NetworkCapabilities} of the network the socket keepalive is on.
+     *
+     * @return Supported keepalive count for the given {@link NetworkCapabilities}.
+     */
+    public static int getSupportedKeepalivesForNetworkCapabilities(
+            @NonNull int[] supportedKeepalives, @NonNull NetworkCapabilities nc) {
+        final int[] transports = nc.getTransportTypes();
+        if (transports.length == 0) return 0;
+        int supportedCount = supportedKeepalives[transports[0]];
+        // Iterate through transports and return minimum supported value.
+        for (final int transport : transports) {
+            if (supportedCount > supportedKeepalives[transport]) {
+                supportedCount = supportedKeepalives[transport];
+            }
+        }
+        return supportedCount;
+    }
+}
diff --git a/services/core/java/com/android/server/connectivity/KeepaliveTracker.java b/services/core/java/com/android/server/connectivity/KeepaliveTracker.java
index 77a18e2..4ba88a8 100644
--- a/services/core/java/com/android/server/connectivity/KeepaliveTracker.java
+++ b/services/core/java/com/android/server/connectivity/KeepaliveTracker.java
@@ -29,6 +29,7 @@
 import static android.net.SocketKeepalive.ERROR_INVALID_IP_ADDRESS;
 import static android.net.SocketKeepalive.ERROR_INVALID_NETWORK;
 import static android.net.SocketKeepalive.ERROR_INVALID_SOCKET;
+import static android.net.SocketKeepalive.ERROR_UNSUPPORTED;
 import static android.net.SocketKeepalive.MAX_INTERVAL_SEC;
 import static android.net.SocketKeepalive.MIN_INTERVAL_SEC;
 import static android.net.SocketKeepalive.NO_KEEPALIVE;
@@ -46,6 +47,7 @@
 import android.net.SocketKeepalive.InvalidSocketException;
 import android.net.TcpKeepalivePacketData;
 import android.net.util.IpUtils;
+import android.net.util.KeepaliveUtils;
 import android.os.Binder;
 import android.os.Handler;
 import android.os.IBinder;
@@ -57,6 +59,7 @@
 import android.util.Log;
 import android.util.Pair;
 
+import com.android.internal.R;
 import com.android.internal.util.HexDump;
 import com.android.internal.util.IndentingPrintWriter;
 
@@ -65,6 +68,7 @@
 import java.net.InetSocketAddress;
 import java.net.SocketAddress;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.HashMap;
 
 /**
@@ -90,10 +94,23 @@
     @NonNull
     private final Context mContext;
 
+    // Supported keepalive count for each transport type, can be configured through
+    // config_networkSupportedKeepaliveCount. For better error handling, use
+    // {@link getSupportedKeepalivesForNetworkCapabilities} instead of direct access.
+    @NonNull
+    private final int[] mSupportedKeepalives;
+
+    // Reserved privileged keepalive slots per transport. Caller's permission will be enforced if
+    // the number of remaining keepalive slots is less than or equal to the threshold.
+    private final int mReservedPrivilegedSlots;
+
     public KeepaliveTracker(Context context, Handler handler) {
         mConnectivityServiceHandler = handler;
         mTcpController = new TcpKeepaliveController(handler);
         mContext = context;
+        mSupportedKeepalives = KeepaliveUtils.getSupportedKeepalives(mContext);
+        mReservedPrivilegedSlots = mContext.getResources().getInteger(
+                R.integer.config_reservedPrivilegedKeepaliveSlots);
     }
 
     /**
@@ -115,11 +132,6 @@
         public static final int TYPE_NATT = 1;
         public static final int TYPE_TCP = 2;
 
-        // Max allowed unprivileged keepalive slots per network. Caller's permission will be
-        // enforced if number of existing keepalives reach this limit.
-        // TODO: consider making this limit configurable via resources.
-        private static final int MAX_UNPRIVILEGED_SLOTS = 3;
-
         // Keepalive slot. A small integer that identifies this keepalive among the ones handled
         // by this network.
         private int mSlot = NO_KEEPALIVE;
@@ -247,24 +259,42 @@
 
         private int checkPermission() {
             final HashMap<Integer, KeepaliveInfo> networkKeepalives = mKeepalives.get(mNai);
-            int unprivilegedCount = 0;
             if (networkKeepalives == null) {
                 return ERROR_INVALID_NETWORK;
             }
-            for (KeepaliveInfo ki : networkKeepalives.values()) {
-                if (!ki.mPrivileged) {
-                    unprivilegedCount++;
-                }
-                if (unprivilegedCount >= MAX_UNPRIVILEGED_SLOTS) {
-                    return mPrivileged ? SUCCESS : ERROR_INSUFFICIENT_RESOURCES;
-                }
+
+            if (mPrivileged) return SUCCESS;
+
+            final int supported = KeepaliveUtils.getSupportedKeepalivesForNetworkCapabilities(
+                    mSupportedKeepalives, mNai.networkCapabilities);
+
+            int takenUnprivilegedSlots = 0;
+            for (final KeepaliveInfo ki : networkKeepalives.values()) {
+                if (!ki.mPrivileged) ++takenUnprivilegedSlots;
             }
+            if (takenUnprivilegedSlots > supported - mReservedPrivilegedSlots) {
+                return ERROR_INSUFFICIENT_RESOURCES;
+            }
+
+            return SUCCESS;
+        }
+
+        private int checkLimit() {
+            final HashMap<Integer, KeepaliveInfo> networkKeepalives = mKeepalives.get(mNai);
+            if (networkKeepalives == null) {
+                return ERROR_INVALID_NETWORK;
+            }
+            final int supported = KeepaliveUtils.getSupportedKeepalivesForNetworkCapabilities(
+                    mSupportedKeepalives, mNai.networkCapabilities);
+            if (supported == 0) return ERROR_UNSUPPORTED;
+            if (networkKeepalives.size() > supported) return ERROR_INSUFFICIENT_RESOURCES;
             return SUCCESS;
         }
 
         private int isValid() {
             synchronized (mNai) {
                 int error = checkInterval();
+                if (error == SUCCESS) error = checkLimit();
                 if (error == SUCCESS) error = checkPermission();
                 if (error == SUCCESS) error = checkNetworkConnected();
                 if (error == SUCCESS) error = checkSourceAddress();
@@ -669,6 +699,8 @@
     }
 
     public void dump(IndentingPrintWriter pw) {
+        pw.println("Supported Socket keepalives: " + Arrays.toString(mSupportedKeepalives));
+        pw.println("Reserved Privileged keepalives: " + mReservedPrivilegedSlots);
         pw.println("Socket keepalives:");
         pw.increaseIndent();
         for (NetworkAgentInfo nai : mKeepalives.keySet()) {
diff --git a/tests/net/java/android/net/util/KeepaliveUtilsTest.kt b/tests/net/java/android/net/util/KeepaliveUtilsTest.kt
new file mode 100644
index 0000000..814e06e
--- /dev/null
+++ b/tests/net/java/android/net/util/KeepaliveUtilsTest.kt
@@ -0,0 +1,130 @@
+/*
+ * Copyright (C) 2019 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 android.content.Context
+import android.content.res.Resources
+import android.net.NetworkCapabilities
+import android.net.NetworkCapabilities.MAX_TRANSPORT
+import android.net.NetworkCapabilities.TRANSPORT_CELLULAR
+import android.net.NetworkCapabilities.TRANSPORT_ETHERNET
+import android.net.NetworkCapabilities.TRANSPORT_VPN
+import android.net.NetworkCapabilities.TRANSPORT_WIFI
+import androidx.test.filters.SmallTest
+import com.android.internal.R
+import org.junit.Assert.assertArrayEquals
+import org.junit.Assert.assertEquals
+import org.junit.Assert.fail
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+import org.mockito.ArgumentMatchers
+import org.mockito.Mockito.doReturn
+import org.mockito.Mockito.mock
+
+/**
+ * Tests for [KeepaliveUtils].
+ *
+ * Build, install and run with:
+ * atest android.net.util.KeepaliveUtilsTest
+ */
+@RunWith(JUnit4::class)
+@SmallTest
+class KeepaliveUtilsTest {
+
+    // Prepare mocked context with given resource strings.
+    private fun getMockedContextWithStringArrayRes(id: Int, res: Array<out String?>?): Context {
+        val mockRes = mock(Resources::class.java)
+        doReturn(res).`when`(mockRes).getStringArray(ArgumentMatchers.eq(id))
+
+        return mock(Context::class.java).apply {
+            doReturn(mockRes).`when`(this).getResources()
+        }
+    }
+
+    @Test
+    fun testGetSupportedKeepalives() {
+        fun assertRunWithException(res: Array<out String?>?) {
+            try {
+                val mockContext = getMockedContextWithStringArrayRes(
+                        R.array.config_networkSupportedKeepaliveCount, res)
+                KeepaliveUtils.getSupportedKeepalives(mockContext)
+                fail("Expected KeepaliveDeviceConfigurationException")
+            } catch (expected: KeepaliveUtils.KeepaliveDeviceConfigurationException) {
+            }
+        }
+
+        // Check resource with various invalid format.
+        assertRunWithException(null)
+        assertRunWithException(arrayOf<String?>(null))
+        assertRunWithException(arrayOfNulls<String?>(10))
+        assertRunWithException(arrayOf(""))
+        assertRunWithException(arrayOf("3,ABC"))
+        assertRunWithException(arrayOf("6,3,3"))
+        assertRunWithException(arrayOf("5"))
+
+        // Check resource with invalid slots value.
+        assertRunWithException(arrayOf("2,2"))
+        assertRunWithException(arrayOf("3,-1"))
+
+        // Check resource with invalid transport type.
+        assertRunWithException(arrayOf("-1,3"))
+        assertRunWithException(arrayOf("10,3"))
+
+        // Check valid customization generates expected array.
+        val validRes = arrayOf("0,3", "1,0", "4,4")
+        val expectedValidRes = intArrayOf(3, 0, 0, 0, 4, 0, 0, 0)
+
+        val mockContext = getMockedContextWithStringArrayRes(
+                R.array.config_networkSupportedKeepaliveCount, validRes)
+        val actual = KeepaliveUtils.getSupportedKeepalives(mockContext)
+        assertArrayEquals(expectedValidRes, actual)
+    }
+
+    @Test
+    fun testGetSupportedKeepalivesForNetworkCapabilities() {
+        // Mock customized supported keepalives for each transport type, and assuming:
+        //   3 for cellular,
+        //   6 for wifi,
+        //   0 for others.
+        val cust = IntArray(MAX_TRANSPORT + 1).apply {
+            this[TRANSPORT_CELLULAR] = 3
+            this[TRANSPORT_WIFI] = 6
+        }
+
+        val nc = NetworkCapabilities()
+        // Check supported keepalives with single transport type.
+        nc.transportTypes = intArrayOf(TRANSPORT_CELLULAR)
+        assertEquals(3, KeepaliveUtils.getSupportedKeepalivesForNetworkCapabilities(cust, nc))
+
+        // Check supported keepalives with multiple transport types.
+        nc.transportTypes = intArrayOf(TRANSPORT_WIFI, TRANSPORT_VPN)
+        assertEquals(0, KeepaliveUtils.getSupportedKeepalivesForNetworkCapabilities(cust, nc))
+
+        // Check supported keepalives with non-customized transport type.
+        nc.transportTypes = intArrayOf(TRANSPORT_ETHERNET)
+        assertEquals(0, KeepaliveUtils.getSupportedKeepalivesForNetworkCapabilities(cust, nc))
+
+        // Check supported keepalives with undefined transport type.
+        nc.transportTypes = intArrayOf(MAX_TRANSPORT + 1)
+        try {
+            KeepaliveUtils.getSupportedKeepalivesForNetworkCapabilities(cust, nc)
+            fail("Expected ArrayIndexOutOfBoundsException")
+        } catch (expected: ArrayIndexOutOfBoundsException) {
+        }
+    }
+}