diff --git a/HMCL/src/main/java/org/jackhuang/hmcl/setting/GlobalConfig.java b/HMCL/src/main/java/org/jackhuang/hmcl/setting/GlobalConfig.java
index 56288bf0d..23beaad00 100644
--- a/HMCL/src/main/java/org/jackhuang/hmcl/setting/GlobalConfig.java
+++ b/HMCL/src/main/java/org/jackhuang/hmcl/setting/GlobalConfig.java
@@ -21,10 +21,7 @@ import com.google.gson.*;
 import com.google.gson.annotations.JsonAdapter;
 import javafx.beans.InvalidationListener;
 import javafx.beans.Observable;
-import javafx.beans.property.IntegerProperty;
-import javafx.beans.property.SimpleIntegerProperty;
-import javafx.beans.property.SimpleStringProperty;
-import javafx.beans.property.StringProperty;
+import javafx.beans.property.*;
 import javafx.collections.ObservableList;
 import javafx.collections.ObservableMap;
 import javafx.collections.ObservableSet;
@@ -73,6 +70,8 @@ public class GlobalConfig implements Cloneable, Observable {
 
     private StringProperty multiplayerToken = new SimpleStringProperty();
 
+    private BooleanProperty multiplayerRelay = new SimpleBooleanProperty();
+
     private IntegerProperty multiplayerAgreementVersion = new SimpleIntegerProperty(0);
 
     private final Map<String, Object> unknownFields = new HashMap<>();
@@ -114,6 +113,18 @@ public class GlobalConfig implements Cloneable, Observable {
         this.agreementVersion.set(agreementVersion);
     }
 
+    public boolean isMultiplayerRelay() {
+        return multiplayerRelay.get();
+    }
+
+    public BooleanProperty multiplayerRelayProperty() {
+        return multiplayerRelay;
+    }
+
+    public void setMultiplayerRelay(boolean multiplayerRelay) {
+        this.multiplayerRelay.set(multiplayerRelay);
+    }
+
     public int getMultiplayerAgreementVersion() {
         return multiplayerAgreementVersion.get();
     }
@@ -154,6 +165,7 @@ public class GlobalConfig implements Cloneable, Observable {
             JsonObject jsonObject = new JsonObject();
             jsonObject.add("agreementVersion", context.serialize(src.getAgreementVersion()));
             jsonObject.add("multiplayerToken", context.serialize(src.getMultiplayerToken()));
+            jsonObject.add("multiplayerRelay", context.serialize(src.isMultiplayerRelay()));
             jsonObject.add("multiplayerAgreementVersion", context.serialize(src.getMultiplayerAgreementVersion()));
             for (Map.Entry<String, Object> entry : src.unknownFields.entrySet()) {
                 jsonObject.add(entry.getKey(), context.serialize(entry.getValue()));
@@ -171,6 +183,7 @@ public class GlobalConfig implements Cloneable, Observable {
             GlobalConfig config = new GlobalConfig();
             config.setAgreementVersion(Optional.ofNullable(obj.get("agreementVersion")).map(JsonElement::getAsInt).orElse(0));
             config.setMultiplayerToken(Optional.ofNullable(obj.get("multiplayerToken")).map(JsonElement::getAsString).orElse(null));
+            config.setMultiplayerRelay(Optional.ofNullable(obj.get("multiplayerRelay")).map(JsonElement::getAsBoolean).orElse(false));
             config.setMultiplayerAgreementVersion(Optional.ofNullable(obj.get("multiplayerAgreementVersion")).map(JsonElement::getAsInt).orElse(0));
 
             for (Map.Entry<String, JsonElement> entry : obj.entrySet()) {
diff --git a/HMCL/src/main/java/org/jackhuang/hmcl/setting/HMCLAccounts.java b/HMCL/src/main/java/org/jackhuang/hmcl/setting/HMCLAccounts.java
index b13c137fd..0e90c857a 100644
--- a/HMCL/src/main/java/org/jackhuang/hmcl/setting/HMCLAccounts.java
+++ b/HMCL/src/main/java/org/jackhuang/hmcl/setting/HMCLAccounts.java
@@ -33,10 +33,13 @@ import java.util.UUID;
 import static org.jackhuang.hmcl.util.Lang.mapOf;
 import static org.jackhuang.hmcl.util.Pair.pair;
 
-public class HMCLAccounts {
+public final class HMCLAccounts {
 
     private static final ObjectProperty<HMCLAccount> account = new SimpleObjectProperty<>();
 
+    private HMCLAccounts() {
+    }
+
     public static HMCLAccount getAccount() {
         return account.get();
     }
diff --git a/HMCL/src/main/java/org/jackhuang/hmcl/ui/construct/OptionToggleButton.java b/HMCL/src/main/java/org/jackhuang/hmcl/ui/construct/OptionToggleButton.java
index 188abfacc..741a72a12 100644
--- a/HMCL/src/main/java/org/jackhuang/hmcl/ui/construct/OptionToggleButton.java
+++ b/HMCL/src/main/java/org/jackhuang/hmcl/ui/construct/OptionToggleButton.java
@@ -27,10 +27,13 @@ import javafx.geometry.Pos;
 import javafx.scene.control.Label;
 import javafx.scene.layout.BorderPane;
 import javafx.scene.layout.StackPane;
+import javafx.scene.layout.VBox;
 import org.jackhuang.hmcl.ui.FXUtils;
+import org.jackhuang.hmcl.util.StringUtils;
 
 public class OptionToggleButton extends StackPane {
     private final StringProperty title = new SimpleStringProperty();
+    private final StringProperty subtitle = new SimpleStringProperty();
     private final BooleanProperty selected = new SimpleBooleanProperty();
 
     public OptionToggleButton() {
@@ -41,11 +44,15 @@ public class OptionToggleButton extends StackPane {
         RipplerContainer container = new RipplerContainer(pane);
         getChildren().setAll(container);
 
-        Label label = new Label();
-        label.setMouseTransparent(true);
-        label.textProperty().bind(title);
-        pane.setLeft(label);
-        BorderPane.setAlignment(label, Pos.CENTER_LEFT);
+        VBox left = new VBox();
+        Label titleLabel = new Label();
+        titleLabel.setMouseTransparent(true);
+        titleLabel.textProperty().bind(title);
+        Label subtitleLabel = new Label();
+        subtitleLabel.setMouseTransparent(true);
+        subtitleLabel.textProperty().bind(subtitle);
+        pane.setLeft(left);
+        BorderPane.setAlignment(left, Pos.CENTER_LEFT);
 
         JFXToggleButton toggleButton = new JFXToggleButton();
         pane.setRight(toggleButton);
@@ -56,6 +63,14 @@ public class OptionToggleButton extends StackPane {
         container.setOnMouseClicked(e -> {
             toggleButton.setSelected(!toggleButton.isSelected());
         });
+
+        FXUtils.onChangeAndOperate(subtitleProperty(), subtitle -> {
+            if (StringUtils.isNotBlank(subtitle)) {
+                left.getChildren().setAll(titleLabel, subtitleLabel);
+            } else {
+                left.getChildren().setAll(titleLabel);
+            }
+        });
     }
 
     public String getTitle() {
@@ -70,6 +85,18 @@ public class OptionToggleButton extends StackPane {
         this.title.set(title);
     }
 
+    public String getSubtitle() {
+        return subtitle.get();
+    }
+
+    public StringProperty subtitleProperty() {
+        return subtitle;
+    }
+
+    public void setSubtitle(String subtitle) {
+        this.subtitle.set(subtitle);
+    }
+
     public boolean isSelected() {
         return selected.get();
     }
diff --git a/HMCL/src/main/java/org/jackhuang/hmcl/ui/main/FeedbackPage.java b/HMCL/src/main/java/org/jackhuang/hmcl/ui/main/FeedbackPage.java
index 706c742d9..be5fbfc5b 100644
--- a/HMCL/src/main/java/org/jackhuang/hmcl/ui/main/FeedbackPage.java
+++ b/HMCL/src/main/java/org/jackhuang/hmcl/ui/main/FeedbackPage.java
@@ -183,7 +183,7 @@ public class FeedbackPage extends VBox implements PageAware {
             }
             HttpRequest req = HttpRequest.GET(NetworkUtils.withQuery("https://hmcl.huangyuhui.net/api/feedback", query));
             if (account != null) {
-                    req.authorization("Bearer", HMCLAccounts.getAccount().getIdToken())
+                req.authorization("Bearer", HMCLAccounts.getAccount().getIdToken())
                         .header("Authorization-Provider", HMCLAccounts.getAccount().getProvider());
             }
             return req.<List<FeedbackResponse>>getJson(new TypeToken<List<FeedbackResponse>>(){}.getType());
diff --git a/HMCL/src/main/java/org/jackhuang/hmcl/ui/main/RootPage.java b/HMCL/src/main/java/org/jackhuang/hmcl/ui/main/RootPage.java
index bfed711d4..33619b809 100644
--- a/HMCL/src/main/java/org/jackhuang/hmcl/ui/main/RootPage.java
+++ b/HMCL/src/main/java/org/jackhuang/hmcl/ui/main/RootPage.java
@@ -53,7 +53,6 @@ import java.util.Date;
 import java.util.List;
 import java.util.stream.Collectors;
 
-import static org.jackhuang.hmcl.ui.FXUtils.newImage;
 import static org.jackhuang.hmcl.ui.FXUtils.runInFX;
 import static org.jackhuang.hmcl.ui.versions.VersionPage.wrap;
 import static org.jackhuang.hmcl.util.i18n.I18n.i18n;
diff --git a/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerClient.java b/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerClient.java
index 6b81dcabf..e8377c0f1 100644
--- a/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerClient.java
+++ b/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerClient.java
@@ -73,19 +73,22 @@ public class MultiplayerClient extends Thread {
     public void run() {
         LOG.info("Connecting to 127.0.0.1:" + port);
         for (int i = 0; i < 5; i++) {
+            KeepAliveThread keepAliveThread = null;
             try (Socket socket = new Socket(InetAddress.getLoopbackAddress(), port);
                  BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                  BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()))) {
+                MultiplayerServer.Endpoint endpoint = new MultiplayerServer.Endpoint(socket, writer);
                 LOG.info("Connected to 127.0.0.1:" + port);
 
-                socket.setKeepAlive(true);
-
                 writer.write(JsonUtils.UGLY_GSON.toJson(new JoinRequest(MultiplayerManager.CATO_VERSION, id)));
                 writer.newLine();
                 writer.flush();
 
                 LOG.fine("Sent join request with id=" + id);
 
+                keepAliveThread = new KeepAliveThread(endpoint);
+                keepAliveThread.start();
+
                 String line;
                 while ((line = reader.readLine()) != null) {
                     if (isInterrupted()) {
@@ -106,6 +109,7 @@ public class MultiplayerClient extends Thread {
                         onKicked.fireEvent(new Event(this));
 
                         LOG.fine("Kicked by the server");
+                    } else if (response instanceof KeepAliveResponse) {
                     } else {
                         LOG.log(Level.WARNING, "Unrecognized packet from server:" + line);
                     }
@@ -121,12 +125,42 @@ public class MultiplayerClient extends Thread {
                 continue;
             } catch (IOException | JsonParseException e) {
                 e.printStackTrace();
+            } finally {
+                if (keepAliveThread != null) {
+                    keepAliveThread.interrupt();
+                }
             }
         }
         LOG.info("Lost connection to 127.0.0.1:" + port);
         onDisconnected.fireEvent(new Event(this));
     }
 
+    private static class KeepAliveThread extends Thread {
+
+        private final MultiplayerServer.Endpoint endpoint;
+
+        public KeepAliveThread(MultiplayerServer.Endpoint endpoint) {
+            this.endpoint = endpoint;
+        }
+
+        @Override
+        public void run() {
+            while (!isInterrupted()) {
+                try {
+                    endpoint.write(new KeepAliveRequest(System.currentTimeMillis()));
+                } catch (IOException e) {
+                    LOG.log(Level.WARNING, "Failed to send keep alive packet", e);
+                    break;
+                }
+                try {
+                    Thread.sleep(1500);
+                } catch (InterruptedException e) {
+                    break;
+                }
+            }
+        }
+    }
+
     public static class ConnectedEvent extends Event {
         private final int port;
 
diff --git a/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerManager.java b/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerManager.java
index 917c3688d..c6cd62a36 100644
--- a/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerManager.java
+++ b/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerManager.java
@@ -44,10 +44,7 @@ import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.attribute.PosixFilePermission;
-import java.util.Arrays;
-import java.util.Base64;
-import java.util.List;
-import java.util.Set;
+import java.util.*;
 import java.util.concurrent.CancellationException;
 import java.util.concurrent.CompletableFuture;
 import java.util.logging.Level;
@@ -67,7 +64,6 @@ public final class MultiplayerManager {
 
     private static final String REMOTE_ADDRESS = "127.0.0.1";
     private static final String LOCAL_ADDRESS = "0.0.0.0";
-    private static final String MODE = "p2p";
 
     private MultiplayerManager() {
     }
@@ -89,7 +85,7 @@ public final class MultiplayerManager {
         return Metadata.HMCL_DIRECTORY.resolve("libraries").resolve(CATO_PATH);
     }
 
-    public static CompletableFuture<CatoSession> joinSession(String token, String version, String sessionName, String peer, int remotePort, int localPort) throws IncompatibleCatoVersionException {
+    public static CompletableFuture<CatoSession> joinSession(String token, String version, String sessionName, String peer, Mode mode, int remotePort, int localPort) throws IncompatibleCatoVersionException {
         if (!CATO_VERSION.equals(version)) {
             throw new IncompatibleCatoVersionException(version, CATO_VERSION);
         }
@@ -100,12 +96,16 @@ public final class MultiplayerManager {
         }
 
         return CompletableFuture.completedFuture(null).thenComposeAsync(unused -> {
+            if (!isPortAvailable(3478)) {
+                throw new CatoAlreadyStartedException();
+            }
+
             String[] commands = new String[]{exe.toString(),
                     "--token", StringUtils.isBlank(token) ? "new" : token,
                     "--id", peer,
                     "--local", String.format("%s:%d", LOCAL_ADDRESS, localPort),
                     "--remote", String.format("%s:%d", REMOTE_ADDRESS, remotePort),
-                    "--mode", MODE};
+                    "--mode", mode.getName()};
             Process process;
             try {
                 process = new ProcessBuilder()
@@ -137,18 +137,21 @@ public final class MultiplayerManager {
                 client.onConnected().register(connectedEvent -> {
                     try {
                         int port = findAvailablePort();
-                        String command = String.format("net add %s %s:%d %s:%d %s\n", peer, LOCAL_ADDRESS, port, REMOTE_ADDRESS, connectedEvent.getPort(), MODE);
+                        String command = String.format("net add %s %s:%d %s:%d %s\n", peer, LOCAL_ADDRESS, port, REMOTE_ADDRESS, connectedEvent.getPort(), mode.getName());
                         LOG.info("Invoking cato: " + command);
+                        client.setGamePort(port);
                         writer.write(command);
                         writer.newLine();
                         writer.flush();
                         future.complete(session);
                     } catch (IOException e) {
                         future.completeExceptionally(e);
+                        session.stop();
                     }
                 });
                 client.onKicked().register(kickedEvent -> {
                     future.completeExceptionally(new CancellationException());
+                    session.stop();
                 });
                 client.start();
             });
@@ -163,13 +166,16 @@ public final class MultiplayerManager {
             throw new IllegalStateException("Cato file not found");
         }
 
+        if (!isPortAvailable(3478)) {
+            throw new CatoAlreadyStartedException();
+        }
+
         MultiplayerServer server = new MultiplayerServer(gamePort);
         server.startServer();
 
         String[] commands = new String[]{exe.toString(),
                 "--token", StringUtils.isBlank(token) ? "new" : token,
-                "--allows", String.format("%s:%d/%s:%d", REMOTE_ADDRESS, server.getPort(), REMOTE_ADDRESS, gamePort),
-                "--mode", MODE};
+                "--allows", String.format("%s:%d/%s:%d", REMOTE_ADDRESS, server.getPort(), REMOTE_ADDRESS, gamePort)};
         Process process = new ProcessBuilder()
                 .command(commands)
                 .start();
@@ -191,6 +197,14 @@ public final class MultiplayerManager {
         }
     }
 
+    public static boolean isPortAvailable(int port) {
+        try (ServerSocket socket = new ServerSocket(port)) {
+            return true;
+        } catch (IOException e) {
+            return false;
+        }
+    }
+
     public static String getCatoPath() {
         switch (OperatingSystem.CURRENT_OS) {
             case WINDOWS:
@@ -420,4 +434,16 @@ public final class MultiplayerManager {
             return actual;
         }
     }
+
+    public enum Mode {
+        P2P,
+        RELAY;
+
+        String getName() {
+            return name().toLowerCase(Locale.ROOT);
+        }
+    }
+
+    public static class CatoAlreadyStartedException extends RuntimeException {
+    }
 }
diff --git a/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerPage.java b/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerPage.java
index 2f0f3c7ff..90a3ca90c 100644
--- a/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerPage.java
+++ b/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerPage.java
@@ -227,6 +227,9 @@ public class MultiplayerPage extends Control implements DecoratorPage, PageAware
                     });
                 });
                 initCatoSession(session);
+            } catch (MultiplayerManager.CatoAlreadyStartedException e) {
+                LOG.log(Level.WARNING, "Cato already started", e);
+                reject.accept(i18n("multiplayer.session.error.already_started"));
             } catch (Exception e) {
                 LOG.log(Level.WARNING, "Failed to create session", e);
                 reject.accept(i18n("multiplayer.session.create.error"));
@@ -264,7 +267,16 @@ public class MultiplayerPage extends Control implements DecoratorPage, PageAware
             }
 
             try {
-                MultiplayerManager.joinSession(globalConfig().getMultiplayerToken(), invitation.getVersion(), invitation.getSessionName(), invitation.getId(), invitation.getChannelPort(), localPort)
+                MultiplayerManager.joinSession(
+                                globalConfig().getMultiplayerToken(),
+                                invitation.getVersion(),
+                                invitation.getSessionName(),
+                                invitation.getId(),
+                                globalConfig().isMultiplayerRelay() && StringUtils.isNotBlank(globalConfig().getMultiplayerToken())
+                                        ? MultiplayerManager.Mode.RELAY
+                                        : MultiplayerManager.Mode.P2P,
+                                invitation.getChannelPort(),
+                                localPort)
                         .thenAcceptAsync(session -> {
                             initCatoSession(session);
 
@@ -295,9 +307,13 @@ public class MultiplayerPage extends Control implements DecoratorPage, PageAware
                                 LOG.info("Connection rejected by the server");
                                 reject.accept(i18n("multiplayer.session.join.rejected"));
                                 return null;
+                            } else if (throwable instanceof MultiplayerManager.CatoAlreadyStartedException) {
+                                LOG.info("Cato already started");
+                                reject.accept(i18n("multiplayer.session.error.already_started"));
+                                return null;
                             } else {
                                 LOG.log(Level.WARNING, "Failed to join sessoin");
-                                reject.accept(i18n("multiplayer.session.error"));
+                                reject.accept(i18n("multiplayer.session.join.error"));
                             }
                             return null;
                         });
diff --git a/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerPageSkin.java b/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerPageSkin.java
index 1c59ed8c9..7c5625a16 100644
--- a/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerPageSkin.java
+++ b/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerPageSkin.java
@@ -265,6 +265,12 @@ public class MultiplayerPageSkin extends SkinBase<MultiplayerPage> {
 
                 gridPane.addRow(0, new Label(i18n("multiplayer.session.create.token")), tokenField, applyLink);
 
+                OptionToggleButton relay = new OptionToggleButton();
+                relay.disableProperty().bind(tokenField.textProperty().isEmpty());
+                relay.selectedProperty().bindBidirectional(globalConfig().multiplayerRelayProperty());
+                relay.setTitle(i18n("multiplayer.relay"));
+                relay.setSubtitle(i18n("multiplayer.relay.hint"));
+
                 HBox pane = new HBox();
                 pane.setAlignment(Pos.CENTER_LEFT);
 
@@ -280,7 +286,7 @@ public class MultiplayerPageSkin extends SkinBase<MultiplayerPage> {
                         placeholder,
                         FXUtils.segmentToTextFlow(i18n("multiplayer.powered_by"), Controllers::onHyperlinkAction));
 
-                thanksPane.getContent().addAll(gridPane, pane);
+                thanksPane.getContent().addAll(gridPane, relay, pane);
             }
 
             content.getChildren().setAll(
diff --git a/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerServer.java b/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerServer.java
index 64016dd18..e146a43e7 100644
--- a/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerServer.java
+++ b/HMCL/src/main/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerServer.java
@@ -18,6 +18,7 @@
 package org.jackhuang.hmcl.ui.multiplayer;
 
 import com.google.gson.JsonParseException;
+import org.jackhuang.hmcl.event.Event;
 import org.jackhuang.hmcl.event.EventManager;
 import org.jackhuang.hmcl.util.FutureCallback;
 import org.jackhuang.hmcl.util.Lang;
@@ -40,9 +41,10 @@ public class MultiplayerServer extends Thread {
     private FutureCallback<CatoClient> onClientAdding;
     private final EventManager<MultiplayerChannel.CatoClient> onClientAdded = new EventManager<>();
     private final EventManager<MultiplayerChannel.CatoClient> onClientDisconnected = new EventManager<>();
+    private final EventManager<Event> onKeepAlive = new EventManager<>();
 
-    private final Map<String, Client> clients = new ConcurrentHashMap<>();
-    private final Map<String, Client> nameClientMap = new ConcurrentHashMap<>();
+    private final Map<String, Endpoint> clients = new ConcurrentHashMap<>();
+    private final Map<String, Endpoint> nameClientMap = new ConcurrentHashMap<>();
 
     public MultiplayerServer(int gamePort) {
         this.gamePort = gamePort;
@@ -63,6 +65,10 @@ public class MultiplayerServer extends Thread {
         return onClientDisconnected;
     }
 
+    public EventManager<Event> onKeepAlive() {
+        return onKeepAlive;
+    }
+
     public void startServer() throws IOException {
         startServer(0);
     }
@@ -98,7 +104,7 @@ public class MultiplayerServer extends Thread {
     }
 
     public void kickPlayer(CatoClient player) {
-        Client client = nameClientMap.get(player.getUsername());
+        Endpoint client = nameClientMap.get(player.getUsername());
         if (client == null) return;
 
         try {
@@ -119,8 +125,8 @@ public class MultiplayerServer extends Thread {
              BufferedReader reader = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
              BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(clientSocket.getOutputStream()))) {
             clientSocket.setKeepAlive(true);
-            Client client = new Client(clientSocket, writer);
-            clients.put(address, client);
+            Endpoint endpoint = new Endpoint(clientSocket, writer);
+            clients.put(address, endpoint);
 
             String line;
             while ((line = reader.readLine()) != null) {
@@ -137,13 +143,13 @@ public class MultiplayerServer extends Thread {
                     clientName = joinRequest.getUsername();
 
                     CatoClient catoClient = new CatoClient(this, clientName);
-                    nameClientMap.put(clientName, client);
+                    nameClientMap.put(clientName, endpoint);
                     onClientAdded.fireEvent(catoClient);
 
                     if (onClientAdding != null) {
                         onClientAdding.call(catoClient, () -> {
                             try {
-                                client.write(new JoinResponse(gamePort));
+                                endpoint.write(new JoinResponse(gamePort));
                             } catch (IOException e) {
                                 LOG.log(Level.WARNING, "Failed to send join response.", e);
                                 try {
@@ -155,7 +161,7 @@ public class MultiplayerServer extends Thread {
                             }
                         }, msg -> {
                             try {
-                                client.write(new KickResponse(msg));
+                                endpoint.write(new KickResponse(msg));
                                 LOG.info("Rejected join request from id=" + joinRequest.getUsername());
                                 socket.close();
                             } catch (IOException e) {
@@ -163,6 +169,10 @@ public class MultiplayerServer extends Thread {
                             }
                         });
                     }
+                } else if (request instanceof KeepAliveRequest) {
+                    endpoint.write(new KeepAliveResponse(System.currentTimeMillis()));
+
+                    onKeepAlive.fireEvent(new Event(this));
                 } else {
                     LOG.log(Level.WARNING, "Unrecognized packet from client " + targetSocket.getRemoteSocketAddress() + ":" + line);
                 }
@@ -181,11 +191,11 @@ public class MultiplayerServer extends Thread {
         }
     }
 
-    private static class Client {
+    public static class Endpoint {
         public final Socket socket;
         public final BufferedWriter writer;
 
-        public Client(Socket socket, BufferedWriter writer) {
+        public Endpoint(Socket socket, BufferedWriter writer) {
             this.socket = socket;
             this.writer = writer;
         }
diff --git a/HMCL/src/main/resources/assets/lang/I18N.properties b/HMCL/src/main/resources/assets/lang/I18N.properties
index 250ea99cd..d0b1656c4 100644
--- a/HMCL/src/main/resources/assets/lang/I18N.properties
+++ b/HMCL/src/main/resources/assets/lang/I18N.properties
@@ -624,15 +624,17 @@ multiplayer.nat.type.symmetric_udp_firewall=Bad (Symmetric with UDP Firewall)
 multiplayer.nat.type.unknown=Unknown
 multiplayer.powered_by=Multiplayer service is provided by <a href="https://noin.cn">noin.cn</a>. <a href="https://noin.cn/agreement">EULA</a>
 multiplayer.report=Report
+multiplayer.relay=Relay Mode
+multiplayer.relay.hint=For users who has a static token, and whose tested NAT type is bad-symmetric
 multiplayer.session=Room
 multiplayer.session.name.format=%1$s's Room
 multiplayer.session.name.motd=HMCL Multiplayer Session - %s
 multiplayer.session.close=Close Room
 multiplayer.session.close.warning=After closing room, all players joined the room will lost connection. Continue?
 multiplayer.session.copy_room_code=Copy Invitation Code
-multiplayer.session.create=Create Room
-multiplayer.session.create.error=Failed to create multiplayer room.
-multiplayer.session.create.hint=Before creating multiplayer room, you must click "Open LAN Server" in running game, and type the port displayed in game in the blank below.
+multiplayer.session.create=Create Session
+multiplayer.session.create.error=Failed to create multiplayer session.
+multiplayer.session.create.hint=Before creating multiplayer session, you must click "Open LAN Server" in running game, and type the port displayed in game in the blank below.
 multiplayer.session.create.join=Connection request
 multiplayer.session.create.join.prompt=Player %s wants to join the multiplayer session. Accept?
 multiplayer.session.create.members=Members
@@ -642,14 +644,16 @@ multiplayer.session.create.name=Session Name
 multiplayer.session.create.port=Port
 multiplayer.session.create.port.error=Cannot detect game port, you must click "Open LAN Server" in game to enable multiplayer functionality.
 multiplayer.session.create.token=Token
-multiplayer.session.create.token.apply=Apple for static token
+multiplayer.session.create.token.apply=Apply for static token
 multiplayer.session.create.token.prompt=Default randomized. You can apply for your own token at noin.cn (Chinese website). 
+multiplayer.session.error.already_started=Cato service has already started locally. Please check whether there are other multiplayer services served or not. Or you can kill cato process in task manager.
 multiplayer.session.expired=Multiplayer session has expired. You should re-create or re-join a room to continue.
 multiplayer.session.hint=You must click "Open LAN Server" in game in order to enable multiplayer functionality.
-multiplayer.session.join=Join Room
-multiplayer.session.join.hint=You must obtain the invitation code from the gamer who has already created a multiplayer room.
+multiplayer.session.join=Join Session
+multiplayer.session.join.error=Failed to join multiplayer session
+multiplayer.session.join.hint=You must obtain the invitation code from the gamer who has already created a multiplayer session.
 multiplayer.session.join.invitation_code=Invitation code
-multiplayer.session.join.invitation_code.error=Incorrect invitation code. Please obtain invitation code from the player who creates the multiplayer room.
+multiplayer.session.join.invitation_code.error=Incorrect invitation code. Please obtain invitation code from the player who creates the multiplayer session.
 multiplayer.session.join.invitation_code.version=Versions of multiplayer functionalities are not the same among you.
 multiplayer.session.join.kicked=You have been kicked by the session holder. You will lost connection with the multiplayer session.
 multiplayer.session.join.lost_connection=Lost connection with the multiplayer session. Maybe the session is destroyed by the creator, or you cannot establish connection with this session.
diff --git a/HMCL/src/main/resources/assets/lang/I18N_zh.properties b/HMCL/src/main/resources/assets/lang/I18N_zh.properties
index 51d8121f1..e9a2b6274 100644
--- a/HMCL/src/main/resources/assets/lang/I18N_zh.properties
+++ b/HMCL/src/main/resources/assets/lang/I18N_zh.properties
@@ -624,6 +624,8 @@ multiplayer.nat.type.symmetric_udp_firewall=差（對稱型+防火牆）
 multiplayer.nat.type.unknown=未知
 multiplayer.powered_by=多人聯機服務由 這裡 (<a href="https://noin.cn">noin.cn</a>) 提供。<a href="https://noin.cn/agreement">用戶協議與免責聲明</a>
 multiplayer.report=違法違規檢舉
+multiplayer.relay=中繼模式
+multiplayer.relay.hint=NAT 網路類型為差-對稱型的用戶，若無法聯機，申請靜態 Token 後可以啟用本選項
 multiplayer.session=房間
 multiplayer.session.name.format=%1$s 的房間
 multiplayer.session.name.motd=HMCL 多人聯機房間 - %s
@@ -644,8 +646,10 @@ multiplayer.session.create.port.error=無法檢測遊戲埠號，你必須先啟
 multiplayer.session.create.token=Token
 multiplayer.session.create.token.apply=申請靜態 Token
 multiplayer.session.create.token.prompt=預設為臨時 Token。你可以在 noin.cn 上申請靜態 Token 並填寫至此處 
+multiplayer.session.error.already_started=本地已經開啟 cato 服務，請檢查是否有其他 HMCL 正在運行聯機服務。或者你可以在任務管理器裡殺掉 cato 進程以繼續。
 multiplayer.session.expired=聯機會話連續使用時間超過了 3 小時，你需要重新創建/加入房間以繼續聯機。
 multiplayer.session.join=加入房間
+multiplayer.session.join.error=加入房間失敗
 multiplayer.session.join.hint=你需要向已經創建好房間的玩家索要邀請碼以便加入多人聯機房間
 multiplayer.session.join.invitation_code=邀請碼
 multiplayer.session.join.invitation_code.error=邀請碼不正確，請向開服玩家獲取邀請碼
diff --git a/HMCL/src/main/resources/assets/lang/I18N_zh_CN.properties b/HMCL/src/main/resources/assets/lang/I18N_zh_CN.properties
index c8c8c3bb0..3a1a8a96e 100644
--- a/HMCL/src/main/resources/assets/lang/I18N_zh_CN.properties
+++ b/HMCL/src/main/resources/assets/lang/I18N_zh_CN.properties
@@ -623,6 +623,8 @@ multiplayer.nat.type.symmetric=差（对称型）
 multiplayer.nat.type.symmetric_udp_firewall=差（对称型+防火墙）
 multiplayer.nat.type.unknown=未知
 multiplayer.powered_by=多人联机服务由 这里 (<a href="https://noin.cn">noin.cn</a>) 提供。<a href="https://noin.cn/agreement">用户协议与免责声明</a>
+multiplayer.relay=中继模式
+multiplayer.relay.hint=NAT 网络类型为差-对称型的用户，若无法联机，申请静态 Token 后可以启用本选项
 multiplayer.report=违法违规举报
 multiplayer.session=房间
 multiplayer.session.name.format=%1$s 的房间
@@ -644,8 +646,10 @@ multiplayer.session.create.port.error=无法检测游戏端口号，你必须先
 multiplayer.session.create.token=Token
 multiplayer.session.create.token.apply=申请静态 Token
 multiplayer.session.create.token.prompt=默认为临时 Token。你可以在 noin.cn 上申请静态 Token 并填写至此处 
+multiplayer.session.error.already_started=本地已经开启 cato 服务，请检查是否有其他 HMCL 正在运行联机服务。或者你可以在任务管理器里杀掉 cato 进程以继续。
 multiplayer.session.expired=联机会话连续使用时间超过了 3 小时，你需要重新创建/加入房间以继续联机。
 multiplayer.session.join=加入房间
+multiplayer.session.join.error=加入房间失败
 multiplayer.session.join.hint=你需要向已经创建好房间的玩家索要邀请码以便加入多人联机房间
 multiplayer.session.join.invitation_code=邀请码
 multiplayer.session.join.invitation_code.error=邀请码不正确，请向开服玩家获取邀请码
diff --git a/HMCL/src/test/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerClientServerTest.java b/HMCL/src/test/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerClientServerTest.java
index e4b602ddf..e1d4022f5 100644
--- a/HMCL/src/test/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerClientServerTest.java
+++ b/HMCL/src/test/java/org/jackhuang/hmcl/ui/multiplayer/MultiplayerClientServerTest.java
@@ -18,13 +18,13 @@
 package org.jackhuang.hmcl.ui.multiplayer;
 
 import org.jackhuang.hmcl.util.Logging;
-import org.junit.Assert;
+import org.junit.Ignore;
 import org.junit.Test;
 
 public class MultiplayerClientServerTest {
 
     @Test
-//    @Ignore
+    @Ignore
     public void startServer() throws Exception {
         Logging.initForTest();
         MultiplayerServer server = new MultiplayerServer(1000);
@@ -33,8 +33,7 @@ public class MultiplayerClientServerTest {
         MultiplayerClient client = new MultiplayerClient("username", 44444);
         client.start();
 
-        server.onClientAdded().register(event -> {
-            Assert.assertEquals("username", event.getUsername());
+        server.onKeepAlive().register(event -> {
             client.interrupt();
             server.interrupt();
         });