diff --git a/core/java/android/net/IIpSecService.aidl b/core/java/android/net/IIpSecService.aidl
index d6774d4..933256a 100644
--- a/core/java/android/net/IIpSecService.aidl
+++ b/core/java/android/net/IIpSecService.aidl
@@ -58,6 +58,9 @@
             in LinkAddress localAddr,
             in String callingPackage);
 
+    void setNetworkForTunnelInterface(
+            int tunnelResourceId, in Network underlyingNetwork, in String callingPackage);
+
     void deleteTunnelInterface(int resourceId, in String callingPackage);
 
     IpSecTransformResponse createTransform(
diff --git a/core/java/android/net/IpSecManager.java b/core/java/android/net/IpSecManager.java
index 70bca30..55fdafc 100644
--- a/core/java/android/net/IpSecManager.java
+++ b/core/java/android/net/IpSecManager.java
@@ -782,6 +782,43 @@
             }
         }
 
+        /**
+         * Update the underlying network for this IpSecTunnelInterface.
+         *
+         * <p>This new underlying network will be used for all transforms applied AFTER this call is
+         * complete. Before new {@link IpSecTransform}(s) with matching addresses are applied to
+         * this tunnel interface, traffic will still use the old SA, and be routed on the old
+         * underlying network.
+         *
+         * <p>To migrate IPsec tunnel mode traffic, a caller should:
+         *
+         * <ol>
+         *   <li>Update the IpSecTunnelInterface’s underlying network.
+         *   <li>Apply {@link IpSecTransform}(s) with matching addresses to this
+         *       IpSecTunnelInterface.
+         * </ol>
+         *
+         * @param underlyingNetwork the new {@link Network} that will carry traffic for this tunnel.
+         *     This network MUST never be the network exposing this IpSecTunnelInterface, otherwise
+         *     this method will throw an {@link IllegalArgumentException}.
+         * @hide
+         */
+        // TODO: b/169171001 Update the documentation when transform migration is supported.
+        // The purpose of making updating network and applying transforms separate is to leave open
+        // the possibility to support lossless migration procedures. To do that, Android platform
+        // will need to support multiple inbound tunnel mode transforms, just like it can support
+        // multiple transport mode transforms.
+        @RequiresFeature(PackageManager.FEATURE_IPSEC_TUNNELS)
+        @RequiresPermission(android.Manifest.permission.MANAGE_IPSEC_TUNNELS)
+        public void setUnderlyingNetwork(@NonNull Network underlyingNetwork) throws IOException {
+            try {
+                mService.setNetworkForTunnelInterface(
+                        mResourceId, underlyingNetwork, mOpPackageName);
+            } catch (RemoteException e) {
+                throw e.rethrowFromSystemServer();
+            }
+        }
+
         private IpSecTunnelInterface(@NonNull Context ctx, @NonNull IIpSecService service,
                 @NonNull InetAddress localAddress, @NonNull InetAddress remoteAddress,
                 @NonNull Network underlyingNetwork)
diff --git a/services/core/java/com/android/server/IpSecService.java b/services/core/java/com/android/server/IpSecService.java
index f648c3e..b48bc90 100644
--- a/services/core/java/com/android/server/IpSecService.java
+++ b/services/core/java/com/android/server/IpSecService.java
@@ -29,6 +29,7 @@
 import android.app.AppOpsManager;
 import android.content.Context;
 import android.content.pm.PackageManager;
+import android.net.ConnectivityManager;
 import android.net.IIpSecService;
 import android.net.INetd;
 import android.net.InetAddresses;
@@ -41,6 +42,7 @@
 import android.net.IpSecTunnelInterfaceResponse;
 import android.net.IpSecUdpEncapResponse;
 import android.net.LinkAddress;
+import android.net.LinkProperties;
 import android.net.Network;
 import android.net.TrafficStats;
 import android.net.util.NetdService;
@@ -797,9 +799,15 @@
         }
     }
 
-    private final class TunnelInterfaceRecord extends OwnedResourceRecord {
+    /**
+     * Tracks an tunnel interface, and manages cleanup paths.
+     *
+     * <p>This class is not thread-safe, and expects that that users of this class will ensure
+     * synchronization and thread safety by holding the IpSecService.this instance lock
+     */
+    @VisibleForTesting
+    final class TunnelInterfaceRecord extends OwnedResourceRecord {
         private final String mInterfaceName;
-        private final Network mUnderlyingNetwork;
 
         // outer addresses
         private final String mLocalAddress;
@@ -810,6 +818,8 @@
 
         private final int mIfId;
 
+        private Network mUnderlyingNetwork;
+
         TunnelInterfaceRecord(
                 int resourceId,
                 String interfaceName,
@@ -870,14 +880,22 @@
             releaseNetId(mOkey);
         }
 
-        public String getInterfaceName() {
-            return mInterfaceName;
+        @GuardedBy("IpSecService.this")
+        public void setUnderlyingNetwork(Network underlyingNetwork) {
+            // When #applyTunnelModeTransform is called, this new underlying network will be used to
+            // update the output mark of the input transform.
+            mUnderlyingNetwork = underlyingNetwork;
         }
 
+        @GuardedBy("IpSecService.this")
         public Network getUnderlyingNetwork() {
             return mUnderlyingNetwork;
         }
 
+        public String getInterfaceName() {
+            return mInterfaceName;
+        }
+
         /** Returns the local, outer address for the tunnelInterface */
         public String getLocalAddress() {
             return mLocalAddress;
@@ -1429,6 +1447,34 @@
         }
     }
 
+    /** Set TunnelInterface to use a specific underlying network. */
+    @Override
+    public synchronized void setNetworkForTunnelInterface(
+            int tunnelResourceId, Network underlyingNetwork, String callingPackage) {
+        enforceTunnelFeatureAndPermissions(callingPackage);
+        Objects.requireNonNull(underlyingNetwork, "No underlying network was specified");
+
+        final UserRecord userRecord = mUserResourceTracker.getUserRecord(Binder.getCallingUid());
+
+        // Get tunnelInterface record; if no such interface is found, will throw
+        // IllegalArgumentException. userRecord.mTunnelInterfaceRecords is never null
+        final TunnelInterfaceRecord tunnelInterfaceInfo =
+                userRecord.mTunnelInterfaceRecords.getResourceOrThrow(tunnelResourceId);
+
+        final ConnectivityManager connectivityManager =
+                mContext.getSystemService(ConnectivityManager.class);
+        final LinkProperties lp = connectivityManager.getLinkProperties(underlyingNetwork);
+        if (tunnelInterfaceInfo.getInterfaceName().equals(lp.getInterfaceName())) {
+            throw new IllegalArgumentException(
+                    "Underlying network cannot be the network being exposed by this tunnel");
+        }
+
+        // It is meaningless to check if the network exists or is valid because the network might
+        // disconnect at any time after it passes the check.
+
+        tunnelInterfaceInfo.setUnderlyingNetwork(underlyingNetwork);
+    }
+
     /**
      * Delete a TunnelInterface that has been been allocated by and registered with the system
      * server