diff --git a/framework/api/current.txt b/framework/api/current.txt
index 7bc0cf3..32dcfd9 100644
--- a/framework/api/current.txt
+++ b/framework/api/current.txt
@@ -151,6 +151,7 @@
     method public void onLinkPropertiesChanged(@NonNull android.net.Network, @NonNull android.net.LinkProperties);
     method public void onLosing(@NonNull android.net.Network, int);
     method public void onLost(@NonNull android.net.Network);
+    method @FlaggedApi("com.android.net.flags.ipv6_over_ble") public void onReserved(@NonNull android.net.NetworkCapabilities);
     method public void onUnavailable();
     field public static final int FLAG_INCLUDE_LOCATION_INFO = 1; // 0x1
   }
diff --git a/framework/src/android/net/ConnectivityManager.java b/framework/src/android/net/ConnectivityManager.java
index 009344d..33a443e 100644
--- a/framework/src/android/net/ConnectivityManager.java
+++ b/framework/src/android/net/ConnectivityManager.java
@@ -4417,6 +4417,28 @@
         }
         private static final int METHOD_ONBLOCKEDSTATUSCHANGED_INT = 14;
 
+        /**
+         * Called when a network is reserved.
+         *
+         * The reservation includes the {@link NetworkCapabilities} that uniquely describe the
+         * network that was reserved. the caller communicates this information to hardware or
+         * software components on or off-device to instruct them to create a network matching this
+         * reservation.
+         *
+         * {@link #onReserved(NetworkCapabilities)} is called at most once and is guaranteed to be
+         * called before any other callback unless the reservation is unavailable.
+         *
+         * Once a reservation is made, the reserved {@link NetworkCapabilities} will not be updated,
+         * and the reservation remains in place until the reserved network connects or {@link
+         * #onUnavailable} is called.
+         *
+         * @param networkCapabilities The {@link NetworkCapabilities} of the reservation.
+         */
+        @FlaggedApi(Flags.FLAG_IPV6_OVER_BLE)
+        @FilteredCallback(methodId = METHOD_ONRESERVED, calledByCallbackId = CALLBACK_RESERVED)
+        public void onReserved(@NonNull NetworkCapabilities networkCapabilities) {}
+        private static final int METHOD_ONRESERVED = 15;
+
         private NetworkRequest networkRequest;
         private final int mFlags;
     }
@@ -4468,6 +4490,8 @@
     public static final int CALLBACK_BLK_CHANGED                = 11;
     /** @hide */
     public static final int CALLBACK_LOCAL_NETWORK_INFO_CHANGED = 12;
+    /** @hide */
+    public static final int CALLBACK_RESERVED                   = 13;
     // When adding new IDs, note CallbackQueue assumes callback IDs are at most 16 bits.
 
 
@@ -4487,6 +4511,7 @@
             case CALLBACK_RESUMED:      return "CALLBACK_RESUMED";
             case CALLBACK_BLK_CHANGED:  return "CALLBACK_BLK_CHANGED";
             case CALLBACK_LOCAL_NETWORK_INFO_CHANGED: return "CALLBACK_LOCAL_NETWORK_INFO_CHANGED";
+            case CALLBACK_RESERVED:     return "CALLBACK_RESERVED";
             default:
                 return Integer.toString(whichCallback);
         }
@@ -4517,6 +4542,7 @@
     public static class NetworkCallbackMethodsHolder {
         public static final NetworkCallbackMethod[] NETWORK_CB_METHODS =
                 new NetworkCallbackMethod[] {
+                        method("onReserved", 1 << CALLBACK_RESERVED, NetworkCapabilities.class),
                         method("onPreCheck", 1 << CALLBACK_PRECHECK, Network.class),
                         // Note the final overload of onAvailable is not included, since it cannot
                         // match any overridden method.
@@ -4596,6 +4622,11 @@
             }
 
             switch (message.what) {
+                case CALLBACK_RESERVED: {
+                    final NetworkCapabilities cap = getObject(message, NetworkCapabilities.class);
+                    callback.onReserved(cap);
+                    break;
+                }
                 case CALLBACK_PRECHECK: {
                     callback.onPreCheck(network);
                     break;
diff --git a/framework/src/android/net/NetworkRequest.java b/framework/src/android/net/NetworkRequest.java
index 5ae25ab..b95363a 100644
--- a/framework/src/android/net/NetworkRequest.java
+++ b/framework/src/android/net/NetworkRequest.java
@@ -32,6 +32,7 @@
 import static android.net.NetworkCapabilities.NET_CAPABILITY_TEMPORARILY_NOT_METERED;
 import static android.net.NetworkCapabilities.NET_CAPABILITY_TRUSTED;
 import static android.net.NetworkCapabilities.NET_CAPABILITY_VALIDATED;
+import static android.net.NetworkCapabilities.RES_ID_UNSET;
 import static android.net.NetworkCapabilities.TRANSPORT_TEST;
 
 import android.annotation.FlaggedApi;
@@ -256,6 +257,9 @@
         if (nc == null) {
             throw new NullPointerException();
         }
+        if (nc.getReservationId() != RES_ID_UNSET) {
+            throw new IllegalArgumentException("ReservationId must only be set by the system");
+        }
         requestId = rId;
         networkCapabilities = nc;
         if (type == Type.RESERVATION) {
diff --git a/service/src/com/android/server/ConnectivityService.java b/service/src/com/android/server/ConnectivityService.java
index bad7246..d9988eb 100644
--- a/service/src/com/android/server/ConnectivityService.java
+++ b/service/src/com/android/server/ConnectivityService.java
@@ -48,6 +48,7 @@
 import static android.net.ConnectivityManager.CALLBACK_LOSING;
 import static android.net.ConnectivityManager.CALLBACK_LOST;
 import static android.net.ConnectivityManager.CALLBACK_PRECHECK;
+import static android.net.ConnectivityManager.CALLBACK_RESERVED;
 import static android.net.ConnectivityManager.CALLBACK_RESUMED;
 import static android.net.ConnectivityManager.CALLBACK_SUSPENDED;
 import static android.net.ConnectivityManager.CALLBACK_UNAVAIL;
@@ -8211,6 +8212,7 @@
         flags = maybeAppendDeclaredMethod(flags, CALLBACK_BLK_CHANGED, "BLK", sb);
         flags = maybeAppendDeclaredMethod(flags, CALLBACK_LOCAL_NETWORK_INFO_CHANGED,
                 "LOCALINF", sb);
+        flags = maybeAppendDeclaredMethod(flags, CALLBACK_RESERVED, "RES", sb);
         if (flags != 0) {
             sb.append("|0x").append(Integer.toHexString(flags));
         }
diff --git a/staticlibs/testutils/devicetests/com/android/testutils/TestableNetworkCallback.kt b/staticlibs/testutils/devicetests/com/android/testutils/TestableNetworkCallback.kt
index ae43c15..d9c51e5 100644
--- a/staticlibs/testutils/devicetests/com/android/testutils/TestableNetworkCallback.kt
+++ b/staticlibs/testutils/devicetests/com/android/testutils/TestableNetworkCallback.kt
@@ -32,6 +32,7 @@
 import com.android.testutils.RecorderCallback.CallbackEntry.LocalInfoChanged
 import com.android.testutils.RecorderCallback.CallbackEntry.Losing
 import com.android.testutils.RecorderCallback.CallbackEntry.Lost
+import com.android.testutils.RecorderCallback.CallbackEntry.Reserved
 import com.android.testutils.RecorderCallback.CallbackEntry.Resumed
 import com.android.testutils.RecorderCallback.CallbackEntry.Suspended
 import com.android.testutils.RecorderCallback.CallbackEntry.Unavailable
@@ -66,6 +67,12 @@
         // constructor by specifying override.
         abstract val network: Network
 
+        data class Reserved private constructor(
+                override val network: Network,
+                val caps: NetworkCapabilities
+        ): CallbackEntry() {
+            constructor(caps: NetworkCapabilities) : this(NULL_NETWORK, caps)
+        }
         data class Available(override val network: Network) : CallbackEntry()
         data class CapabilitiesChanged(
             override val network: Network,
@@ -100,6 +107,8 @@
         // Convenience constants for expecting a type
         companion object {
             @JvmField
+            val RESERVED = Reserved::class
+            @JvmField
             val AVAILABLE = Available::class
             @JvmField
             val NETWORK_CAPS_UPDATED = CapabilitiesChanged::class
@@ -127,6 +136,11 @@
     val history = backingRecord.newReadHead()
     val mark get() = history.mark
 
+    override fun onReserved(caps: NetworkCapabilities) {
+        Log.d(logTag, "onReserved $caps")
+        history.add(Reserved(caps))
+    }
+
     override fun onAvailable(network: Network) {
         Log.d(logTag, "onAvailable $network")
         history.add(Available(network))
diff --git a/staticlibs/testutils/devicetests/com/android/testutils/TestableNetworkOfferCallback.kt b/staticlibs/testutils/devicetests/com/android/testutils/TestableNetworkOfferCallback.kt
index 21bd60c..a0078d2 100644
--- a/staticlibs/testutils/devicetests/com/android/testutils/TestableNetworkOfferCallback.kt
+++ b/staticlibs/testutils/devicetests/com/android/testutils/TestableNetworkOfferCallback.kt
@@ -52,10 +52,11 @@
 
     inline fun <reified T : CallbackEntry> expectCallbackThat(
         crossinline predicate: (T) -> Boolean
-    ) {
+    ): T {
         val event = history.poll(timeoutMs)
                 ?: fail("Did not receive callback after ${timeoutMs}ms")
         if (event !is T || !predicate(event)) fail("Received unexpected callback $event")
+        return event
     }
 
     fun expectOnNetworkNeeded(capabilities: NetworkCapabilities) =
diff --git a/tests/cts/net/src/android/net/cts/NetworkRequestTest.java b/tests/cts/net/src/android/net/cts/NetworkRequestTest.java
index 2226f4c..1ca5a77 100644
--- a/tests/cts/net/src/android/net/cts/NetworkRequestTest.java
+++ b/tests/cts/net/src/android/net/cts/NetworkRequestTest.java
@@ -42,6 +42,7 @@
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assume.assumeTrue;
 
@@ -583,4 +584,15 @@
         assertTrue(requestNR.canBeSatisfiedBy(otherSpecificOffer));
         assertTrue(requestNR.canBeSatisfiedBy(regularOffer));
     }
+
+    @Test
+    @IgnoreUpTo(Build.VERSION_CODES.R)
+    public void testNetworkRequest_throwsWhenPassingCapsWithReservationId() {
+        final NetworkCapabilities capsWithResId = new NetworkCapabilities();
+        capsWithResId.setReservationId(42);
+
+        assertThrows(IllegalArgumentException.class, () -> {
+            new NetworkRequest(capsWithResId, TYPE_NONE, 42 /* rId */, NetworkRequest.Type.REQUEST);
+        });
+    }
 }
diff --git a/tests/unit/java/com/android/server/connectivityservice/CSDeclaredMethodsForCallbacksTest.kt b/tests/unit/java/com/android/server/connectivityservice/CSDeclaredMethodsForCallbacksTest.kt
index a7083dc..b179aac 100644
--- a/tests/unit/java/com/android/server/connectivityservice/CSDeclaredMethodsForCallbacksTest.kt
+++ b/tests/unit/java/com/android/server/connectivityservice/CSDeclaredMethodsForCallbacksTest.kt
@@ -150,7 +150,7 @@
         // EXPIRE_LEGACY_REQUEST (=8) is only used in ConnectivityManager and not included.
         // CALLBACK_TRANSITIVE_CALLS_ONLY (=0) is not a callback so not included either.
         assertEquals(
-            "PRECHK|AVAIL|LOSING|LOST|UNAVAIL|NC|LP|SUSP|RESUME|BLK|LOCALINF|0x7fffe101",
+            "PRECHK|AVAIL|LOSING|LOST|UNAVAIL|NC|LP|SUSP|RESUME|BLK|LOCALINF|RES|0x7fffc101",
             ConnectivityService.declaredMethodsFlagsToString(0x7fff_ffff)
         )
         // The toString method and the assertion above need to be updated if constants are added
@@ -158,7 +158,7 @@
             Modifier.isStatic(it.modifiers) && Modifier.isFinal(it.modifiers) &&
                     it.name.startsWith("CALLBACK_")
         }
-        assertEquals(12, constants.size)
+        assertEquals(13, constants.size)
     }
 }