diff --git a/common/networkstackclient/Android.bp b/common/networkstackclient/Android.bp
index 983bb61..3696e92 100644
--- a/common/networkstackclient/Android.bp
+++ b/common/networkstackclient/Android.bp
@@ -102,6 +102,8 @@
         // New AIDL classes should go into android.net.networkstack.aidl so they can be clearly
         // identified
         "src/android/net/networkstack/aidl/dhcp/DhcpOption.aidl",
+        "src/android/net/networkstack/aidl/ip/ReachabilityLossInfoParcelable.aidl",
+        "src/android/net/networkstack/aidl/ip/ReachabilityLossReason.aidl",
     ],
     backend: {
         java: {
diff --git a/common/networkstackclient/aidl_api/networkstack-aidl-interfaces/current/android/net/ip/IIpClientCallbacks.aidl b/common/networkstackclient/aidl_api/networkstack-aidl-interfaces/current/android/net/ip/IIpClientCallbacks.aidl
index 488510d..24bbf64 100644
--- a/common/networkstackclient/aidl_api/networkstack-aidl-interfaces/current/android/net/ip/IIpClientCallbacks.aidl
+++ b/common/networkstackclient/aidl_api/networkstack-aidl-interfaces/current/android/net/ip/IIpClientCallbacks.aidl
@@ -48,4 +48,5 @@
   oneway void setFallbackMulticastFilter(boolean enabled);
   oneway void setNeighborDiscoveryOffload(boolean enable);
   oneway void onPreconnectionStart(in List<android.net.Layer2PacketParcelable> packets);
+  oneway void onReachabilityFailure(in android.net.networkstack.aidl.ip.ReachabilityLossInfoParcelable lossInfo);
 }
diff --git a/common/networkstackclient/aidl_api/networkstack-aidl-interfaces/current/android/net/networkstack/aidl/ip/ReachabilityLossInfoParcelable.aidl b/common/networkstackclient/aidl_api/networkstack-aidl-interfaces/current/android/net/networkstack/aidl/ip/ReachabilityLossInfoParcelable.aidl
new file mode 100644
index 0000000..bb88434
--- /dev/null
+++ b/common/networkstackclient/aidl_api/networkstack-aidl-interfaces/current/android/net/networkstack/aidl/ip/ReachabilityLossInfoParcelable.aidl
@@ -0,0 +1,39 @@
+/*
+ * 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.
+ */
+///////////////////////////////////////////////////////////////////////////////
+// THIS FILE IS IMMUTABLE. DO NOT EDIT IN ANY CASE.                          //
+///////////////////////////////////////////////////////////////////////////////
+
+// This file is a snapshot of an AIDL file. Do not edit it manually. There are
+// two cases:
+// 1). this is a frozen version file - do not edit this in any case.
+// 2). this is a 'current' file. If you make a backwards compatible change to
+//     the interface (from the latest frozen version), the build system will
+//     prompt you to update this file with `m <name>-update-api`.
+//
+// You must not make a backward incompatible change to any AIDL file built
+// with the aidl_interface module type with versions property set. The module
+// type is used to build AIDL files in a way that they can be used across
+// independently updatable components of the system. If a device is shipped
+// with such a backward incompatible change, it has a high risk of breaking
+// later when a module using the interface is updated, e.g., Mainline modules.
+
+package android.net.networkstack.aidl.ip;
+@JavaDerive(equals=true, toString=true) @JavaOnlyImmutable
+parcelable ReachabilityLossInfoParcelable {
+  String message;
+  android.net.networkstack.aidl.ip.ReachabilityLossReason reason;
+}
diff --git a/common/networkstackclient/aidl_api/networkstack-aidl-interfaces/current/android/net/networkstack/aidl/ip/ReachabilityLossReason.aidl b/common/networkstackclient/aidl_api/networkstack-aidl-interfaces/current/android/net/networkstack/aidl/ip/ReachabilityLossReason.aidl
new file mode 100644
index 0000000..70a7db2
--- /dev/null
+++ b/common/networkstackclient/aidl_api/networkstack-aidl-interfaces/current/android/net/networkstack/aidl/ip/ReachabilityLossReason.aidl
@@ -0,0 +1,40 @@
+/*
+ * 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.
+ */
+///////////////////////////////////////////////////////////////////////////////
+// THIS FILE IS IMMUTABLE. DO NOT EDIT IN ANY CASE.                          //
+///////////////////////////////////////////////////////////////////////////////
+
+// This file is a snapshot of an AIDL file. Do not edit it manually. There are
+// two cases:
+// 1). this is a frozen version file - do not edit this in any case.
+// 2). this is a 'current' file. If you make a backwards compatible change to
+//     the interface (from the latest frozen version), the build system will
+//     prompt you to update this file with `m <name>-update-api`.
+//
+// You must not make a backward incompatible change to any AIDL file built
+// with the aidl_interface module type with versions property set. The module
+// type is used to build AIDL files in a way that they can be used across
+// independently updatable components of the system. If a device is shipped
+// with such a backward incompatible change, it has a high risk of breaking
+// later when a module using the interface is updated, e.g., Mainline modules.
+
+package android.net.networkstack.aidl.ip;
+@Backing(type="int")
+enum ReachabilityLossReason {
+  ROAM = 0,
+  CONFIRM = 1,
+  ORGANIC = 2,
+}
diff --git a/common/networkstackclient/src/android/net/ip/IIpClientCallbacks.aidl b/common/networkstackclient/src/android/net/ip/IIpClientCallbacks.aidl
index de398ed..932672e 100644
--- a/common/networkstackclient/src/android/net/ip/IIpClientCallbacks.aidl
+++ b/common/networkstackclient/src/android/net/ip/IIpClientCallbacks.aidl
@@ -18,6 +18,7 @@
 import android.net.Layer2PacketParcelable;
 import android.net.LinkProperties;
 import android.net.ip.IIpClient;
+import android.net.networkstack.aidl.ip.ReachabilityLossInfoParcelable;
 import android.net.DhcpResultsParcelable;
 
 /** @hide */
@@ -67,4 +68,8 @@
 
     // Invoked on starting preconnection process.
     void onPreconnectionStart(in List<Layer2PacketParcelable> packets);
+
+    // Called when the internal IpReachabilityMonitor (if enabled) has detected the loss of a
+    // critical number of required neighbors or DHCP roaming fails.
+    void onReachabilityFailure(in ReachabilityLossInfoParcelable lossInfo);
 }
diff --git a/common/networkstackclient/src/android/net/ip/IpClientCallbacks.java b/common/networkstackclient/src/android/net/ip/IpClientCallbacks.java
index b17fcaa..d3e6cb7 100644
--- a/common/networkstackclient/src/android/net/ip/IpClientCallbacks.java
+++ b/common/networkstackclient/src/android/net/ip/IpClientCallbacks.java
@@ -19,6 +19,7 @@
 import android.net.DhcpResultsParcelable;
 import android.net.Layer2PacketParcelable;
 import android.net.LinkProperties;
+import android.net.networkstack.aidl.ip.ReachabilityLossInfoParcelable;
 
 import java.util.List;
 
@@ -133,4 +134,12 @@
      * Invoked on starting preconnection process.
      */
     public void onPreconnectionStart(List<Layer2PacketParcelable> packets) {}
+
+    /**
+     * Called when the internal IpReachabilityMonitor (if enabled) has detected the loss of a
+     * critical number of required neighbors or DHCP roaming fails.
+     *
+     * @param lossInfo the specific neighbor reachability loss information.
+     */
+    public void onReachabilityFailure(ReachabilityLossInfoParcelable lossInfo) {}
 }
diff --git a/common/networkstackclient/src/android/net/ip/IpClientUtil.java b/common/networkstackclient/src/android/net/ip/IpClientUtil.java
index 1b55776..d488578 100644
--- a/common/networkstackclient/src/android/net/ip/IpClientUtil.java
+++ b/common/networkstackclient/src/android/net/ip/IpClientUtil.java
@@ -21,6 +21,7 @@
 import android.net.Layer2PacketParcelable;
 import android.net.LinkProperties;
 import android.net.networkstack.ModuleNetworkStackClient;
+import android.net.networkstack.aidl.ip.ReachabilityLossInfoParcelable;
 import android.os.ConditionVariable;
 
 import java.io.FileDescriptor;
@@ -182,6 +183,13 @@
             mCb.onPreconnectionStart(packets);
         }
 
+        // Called when the internal IpReachabilityMonitor (if enabled) has detected the loss of a
+        // critical number of required neighbors or DHCP roaming fails.
+        @Override
+        public void onReachabilityFailure(ReachabilityLossInfoParcelable lossInfo) {
+            mCb.onReachabilityFailure(lossInfo);
+        }
+
         @Override
         public int getInterfaceVersion() {
             return this.VERSION;
diff --git a/common/networkstackclient/src/android/net/networkstack/aidl/ip/ReachabilityLossInfoParcelable.aidl b/common/networkstackclient/src/android/net/networkstack/aidl/ip/ReachabilityLossInfoParcelable.aidl
new file mode 100644
index 0000000..fda6264
--- /dev/null
+++ b/common/networkstackclient/src/android/net/networkstack/aidl/ip/ReachabilityLossInfoParcelable.aidl
@@ -0,0 +1,28 @@
+/*
+ * 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 android.net.networkstack.aidl.ip;
+
+import android.net.networkstack.aidl.ip.ReachabilityLossReason;
+
+@JavaDerive(equals=true, toString=true) @JavaOnlyImmutable
+parcelable ReachabilityLossInfoParcelable {
+    /** The log message when reachability loss happens. */
+    String message;
+
+    /** The specific reason of reachability loss. */
+    ReachabilityLossReason reason;
+}
diff --git a/common/networkstackclient/src/android/net/networkstack/aidl/ip/ReachabilityLossReason.aidl b/common/networkstackclient/src/android/net/networkstack/aidl/ip/ReachabilityLossReason.aidl
new file mode 100644
index 0000000..cc2e9e7
--- /dev/null
+++ b/common/networkstackclient/src/android/net/networkstack/aidl/ip/ReachabilityLossReason.aidl
@@ -0,0 +1,24 @@
+/*
+ * 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 android.net.networkstack.aidl.ip;
+
+@Backing(type="int")
+enum ReachabilityLossReason {
+    ROAM,    // reachability loss due to L2 roaming.
+    CONFIRM, // reachability loss due to WiFi RSSI check.
+    ORGANIC, // reachability loss notification comes from kernel.
+}