diff --git a/quic/core/http/end_to_end_test.cc b/quic/core/http/end_to_end_test.cc
index 0e4bb8c..9f73f74 100644
--- a/quic/core/http/end_to_end_test.cc
+++ b/quic/core/http/end_to_end_test.cc
@@ -211,8 +211,9 @@
         chlo_multiplier_(0),
         stream_factory_(nullptr),
         support_server_push_(false),
-        override_connection_id_(nullptr),
-        expected_connection_id_length_(kQuicDefaultConnectionIdLength) {
+        override_server_connection_id_(nullptr),
+        override_client_connection_id_(nullptr),
+        expected_server_connection_id_length_(kQuicDefaultConnectionIdLength) {
     SetQuicFlag(FLAGS_quic_supports_tls_handshake, true);
     SetQuicRestartFlag(quic_no_server_conn_ver_negotiation2, true);
     SetQuicReloadableFlag(quic_no_client_conn_ver_negotiation, true);
@@ -259,8 +260,11 @@
     if (!pre_shared_key_client_.empty()) {
       client->client()->SetPreSharedKey(pre_shared_key_client_);
     }
-    if (override_connection_id_ != nullptr) {
-      client->UseConnectionId(*override_connection_id_);
+    if (override_server_connection_id_ != nullptr) {
+      client->UseConnectionId(*override_server_connection_id_);
+    }
+    if (override_client_connection_id_ != nullptr) {
+      client->UseClientConnectionId(*override_client_connection_id_);
     }
     client->Connect();
     return client;
@@ -375,7 +379,7 @@
     auto* test_server = new QuicTestServer(
         crypto_test_utils::ProofSourceForTesting(), server_config_,
         server_supported_versions_, &memory_cache_backend_,
-        expected_connection_id_length_);
+        expected_server_connection_id_length_);
     server_thread_ = QuicMakeUnique<ServerThread>(test_server, server_address_);
     if (chlo_multiplier_ != 0) {
       server_thread_->server()->SetChloMultiplier(chlo_multiplier_);
@@ -538,8 +542,9 @@
   bool support_server_push_;
   std::string pre_shared_key_client_;
   std::string pre_shared_key_server_;
-  QuicConnectionId* override_connection_id_;
-  uint8_t expected_connection_id_length_;
+  QuicConnectionId* override_server_connection_id_;
+  QuicConnectionId* override_client_connection_id_;
+  uint8_t expected_server_connection_id_length_;
 };
 
 // Run all end to end tests with all supported versions.
@@ -603,8 +608,8 @@
 TEST_P(EndToEndTest, SimpleRequestResponseZeroConnectionID) {
   QuicConnectionId connection_id = QuicUtils::CreateZeroConnectionId(
       GetParam().negotiated_version.transport_version);
-  override_connection_id_ = &connection_id;
-  expected_connection_id_length_ = connection_id.length();
+  override_server_connection_id_ = &connection_id;
+  expected_server_connection_id_length_ = connection_id.length();
   ASSERT_TRUE(Initialize());
 
   EXPECT_EQ(kFooResponseBody, client_->SendSynchronousRequest("/foo"));
@@ -628,7 +633,7 @@
   }
   QuicConnectionId connection_id =
       TestConnectionIdNineBytesLong(UINT64_C(0xBADbadBADbad));
-  override_connection_id_ = &connection_id;
+  override_server_connection_id_ = &connection_id;
   ASSERT_TRUE(Initialize());
   EXPECT_EQ(kFooResponseBody, client_->SendSynchronousRequest("/foo"));
   EXPECT_EQ("200", client_->response_headers()->find(":status")->second);
@@ -639,6 +644,43 @@
                                                 .length());
 }
 
+TEST_P(EndToEndTest, ClientConnectionId) {
+  if (!GetParam().negotiated_version.SupportsClientConnectionIds()) {
+    ASSERT_TRUE(Initialize());
+    return;
+  }
+  QuicConnectionId client_connection_id =
+      TestConnectionId(UINT64_C(0xc1c2c3c4c5c6c7c8));
+  override_client_connection_id_ = &client_connection_id;
+  ASSERT_TRUE(Initialize());
+  EXPECT_EQ(kFooResponseBody, client_->SendSynchronousRequest("/foo"));
+  EXPECT_EQ("200", client_->response_headers()->find(":status")->second);
+  EXPECT_EQ(client_connection_id, client_->client()
+                                      ->client_session()
+                                      ->connection()
+                                      ->client_connection_id());
+}
+
+TEST_P(EndToEndTest, ForcedVersionNegotiationAndClientConnectionId) {
+  if (!GetParam().negotiated_version.SupportsClientConnectionIds()) {
+    ASSERT_TRUE(Initialize());
+    return;
+  }
+  client_supported_versions_.insert(client_supported_versions_.begin(),
+                                    QuicVersionReservedForNegotiation());
+  QuicConnectionId client_connection_id =
+      TestConnectionId(UINT64_C(0xc1c2c3c4c5c6c7c8));
+  override_client_connection_id_ = &client_connection_id;
+  ASSERT_TRUE(Initialize());
+  ASSERT_TRUE(ServerSendsVersionNegotiation());
+  EXPECT_EQ(kFooResponseBody, client_->SendSynchronousRequest("/foo"));
+  EXPECT_EQ("200", client_->response_headers()->find(":status")->second);
+  EXPECT_EQ(client_connection_id, client_->client()
+                                      ->client_session()
+                                      ->connection()
+                                      ->client_connection_id());
+}
+
 TEST_P(EndToEndTest, ForcedVersionNegotiationAndBadConnectionIdLength) {
   if (!GetQuicRestartFlag(
           quic_allow_variable_length_connection_id_for_negotiation)) {
@@ -654,7 +696,7 @@
                                     QuicVersionReservedForNegotiation());
   QuicConnectionId connection_id =
       TestConnectionIdNineBytesLong(UINT64_C(0xBADbadBADbad));
-  override_connection_id_ = &connection_id;
+  override_server_connection_id_ = &connection_id;
   ASSERT_TRUE(Initialize());
   ASSERT_TRUE(ServerSendsVersionNegotiation());
   EXPECT_EQ(kFooResponseBody, client_->SendSynchronousRequest("/foo"));
@@ -676,9 +718,9 @@
   // Start client_ which will use a bad connection ID length.
   QuicConnectionId connection_id =
       TestConnectionIdNineBytesLong(UINT64_C(0xBADbadBADbad));
-  override_connection_id_ = &connection_id;
+  override_server_connection_id_ = &connection_id;
   ASSERT_TRUE(Initialize());
-  override_connection_id_ = nullptr;
+  override_server_connection_id_ = nullptr;
 
   // Start client2 which will use a good connection ID length.
   std::unique_ptr<QuicTestClient> client2(CreateQuicClient(nullptr));
@@ -767,8 +809,8 @@
 TEST_P(EndToEndTest, MultipleRequestResponseZeroConnectionID) {
   QuicConnectionId connection_id = QuicUtils::CreateZeroConnectionId(
       GetParam().negotiated_version.transport_version);
-  override_connection_id_ = &connection_id;
-  expected_connection_id_length_ = connection_id.length();
+  override_server_connection_id_ = &connection_id;
+  expected_server_connection_id_length_ = connection_id.length();
   ASSERT_TRUE(Initialize());
 
   EXPECT_EQ(kFooResponseBody, client_->SendSynchronousRequest("/foo"));
@@ -2355,7 +2397,7 @@
       TestConnectionIdToUInt64(client_connection->connection_id()) + 1);
   std::unique_ptr<QuicEncryptedPacket> packet(
       QuicFramer::BuildVersionNegotiationPacket(
-          incorrect_connection_id,
+          incorrect_connection_id, EmptyQuicConnectionId(),
           client_connection->transport_version() > QUIC_VERSION_43,
           server_supported_versions_));
   testing::NiceMock<MockQuicConnectionDebugVisitor> visitor;
diff --git a/quic/core/http/quic_send_control_stream.cc b/quic/core/http/quic_send_control_stream.cc
index 40b6111..8ca7bc8 100644
--- a/quic/core/http/quic_send_control_stream.cc
+++ b/quic/core/http/quic_send_control_stream.cc
@@ -14,7 +14,9 @@
 QuicSendControlStream::QuicSendControlStream(QuicStreamId id,
                                              QuicSpdySession* session)
     : QuicStream(id, session, /*is_static = */ true, WRITE_UNIDIRECTIONAL),
-      settings_sent_(false) {}
+      settings_sent_(false) {
+  DisableConnectionFlowControlForThisStream();
+}
 
 void QuicSendControlStream::OnStreamReset(const QuicRstStreamFrame& frame) {
   // TODO(renjietang) Change the error code to H/3 specific
@@ -26,6 +28,10 @@
 
 void QuicSendControlStream::SendSettingsFrame(const SettingsFrame& settings) {
   DCHECK(!settings_sent_);
+  // Send the stream type byte on the wire so peer knows about this stream.
+  char type[] = {0x00};
+  WriteOrBufferData(QuicStringPiece(type, 1), false, nullptr);
+
   std::unique_ptr<char[]> buffer;
   QuicByteCount frame_length =
       encoder_.SerializeSettingsFrame(settings, &buffer);
@@ -33,5 +39,4 @@
                     /*fin = */ false, nullptr);
   settings_sent_ = true;
 }
-
 }  // namespace quic
diff --git a/quic/core/http/quic_spdy_session.cc b/quic/core/http/quic_spdy_session.cc
index 93d10e1..acc42d8 100644
--- a/quic/core/http/quic_spdy_session.cc
+++ b/quic/core/http/quic_spdy_session.cc
@@ -9,6 +9,21 @@
 #include <string>
 #include <utility>
 
+<<<<<<<
+|||||||
+#include "net/third_party/quic/core/http/quic_headers_stream.h"
+#include "net/third_party/quic/core/quic_utils.h"
+#include "net/third_party/quic/platform/api/quic_bug_tracker.h"
+#include "net/third_party/quic/platform/api/quic_fallthrough.h"
+#include "net/third_party/quic/platform/api/quic_flag_utils.h"
+=======
+#include "net/third_party/quic/core/http/quic_headers_stream.h"
+#include "net/third_party/quic/core/quic_utils.h"
+#include "net/third_party/quic/core/quic_versions.h"
+#include "net/third_party/quic/platform/api/quic_bug_tracker.h"
+#include "net/third_party/quic/platform/api/quic_fallthrough.h"
+#include "net/third_party/quic/platform/api/quic_flag_utils.h"
+>>>>>>>
 #include "net/third_party/quiche/src/quic/core/http/quic_headers_stream.h"
 #include "net/third_party/quiche/src/quic/core/quic_utils.h"
 #include "net/third_party/quiche/src/quic/platform/api/quic_bug_tracker.h"
@@ -361,17 +376,27 @@
     qpack_decoder_ = QuicMakeUnique<QpackDecoder>(this, this);
   }
 
-  headers_stream_ = QuicMakeUnique<QuicHeadersStream>((this));
-  DCHECK_EQ(QuicUtils::GetHeadersStreamId(connection()->transport_version()),
-            headers_stream_->id());
-  if (!eliminate_static_stream_map()) {
-    RegisterStaticStream(
-        QuicUtils::GetHeadersStreamId(connection()->transport_version()),
-        headers_stream_.get());
-  } else {
-    QUIC_RELOADABLE_FLAG_COUNT_N(quic_eliminate_static_stream_map_3, 7, 17);
-    unowned_headers_stream_ = headers_stream_.get();
-    RegisterStaticStreamNew(std::move(headers_stream_));
+  if (!VersionUsesQpack(connection()->transport_version())) {
+    headers_stream_ = QuicMakeUnique<QuicHeadersStream>((this));
+    DCHECK_EQ(QuicUtils::GetHeadersStreamId(connection()->transport_version()),
+              headers_stream_->id());
+    if (!eliminate_static_stream_map()) {
+      RegisterStaticStream(
+          QuicUtils::GetHeadersStreamId(connection()->transport_version()),
+          headers_stream_.get());
+    } else {
+      QUIC_RELOADABLE_FLAG_COUNT_N(quic_eliminate_static_stream_map_3, 7, 17);
+      unowned_headers_stream_ = headers_stream_.get();
+      RegisterStaticStreamNew(std::move(headers_stream_));
+    }
+  }
+
+  if (VersionHasControlStreams(connection()->transport_version()) &&
+      eliminate_static_stream_map()) {
+    auto send_control = QuicMakeUnique<QuicSendControlStream>(
+        GetNextOutgoingUnidirectionalStreamId(), this);
+    send_control_stream_ = send_control.get();
+    RegisterStaticStreamNew(std::move(send_control));
   }
 
   set_max_uncompressed_header_bytes(max_inbound_header_list_size_);
@@ -520,12 +545,17 @@
 }
 
 void QuicSpdySession::SendMaxHeaderListSize(size_t value) {
-  SpdySettingsIR settings_frame;
-  settings_frame.AddSetting(SETTINGS_MAX_HEADER_LIST_SIZE, value);
-
-  SpdySerializedFrame frame(spdy_framer_.SerializeFrame(settings_frame));
-  headers_stream()->WriteOrBufferData(
-      QuicStringPiece(frame.data(), frame.size()), false, nullptr);
+  if (!VersionHasControlStreams(connection()->transport_version())) {
+    SpdySettingsIR settings_frame;
+    settings_frame.AddSetting(SETTINGS_MAX_HEADER_LIST_SIZE, value);
+    SpdySerializedFrame frame(spdy_framer_.SerializeFrame(settings_frame));
+    headers_stream()->WriteOrBufferData(
+        QuicStringPiece(frame.data(), frame.size()), false, nullptr);
+  } else {
+    SettingsFrame settings;
+    settings.values[6] = value;
+    send_control_stream_->SendSettingsFrame(settings);
+  }
 }
 
 QpackEncoder* QuicSpdySession::qpack_encoder() {
@@ -564,7 +594,7 @@
 
 bool QuicSpdySession::UsesPendingStreams() const {
   DCHECK(VersionHasControlStreams(connection()->transport_version()));
-  return false;
+  return true;
 }
 
 size_t QuicSpdySession::WriteHeadersOnHeadersStreamImpl(
@@ -743,15 +773,20 @@
   if (!reader.ReadVarInt62(&stream_type)) {
     return;
   }
-  CreateIncomingStreamFromPending(pending->id(), stream_type);
+  CreateIncomingStreamFromPending(pending, stream_type);
 }
 
-void QuicSpdySession::CreateIncomingStreamFromPending(QuicStreamId id,
+void QuicSpdySession::CreateIncomingStreamFromPending(PendingStream* pending,
                                                       uint64_t stream_type) {
   switch (stream_type) {
-    case 0x00:  // HTTP/3 control stream.
-      // TODO(renjietang): Create incoming control stream.
+    case 0x00: {  // HTTP/3 control stream.
+      auto receive_stream =
+          QuicMakeUnique<QuicReceiveControlStream>(std::move(*pending));
+      receive_control_stream_ = receive_stream.get();
+      RegisterStaticStreamNew(std::move(receive_stream));
+      pending_streams().erase(pending_streams().find(pending->id()));
       break;
+    }
     case 0x01:  // Push Stream.
       break;
     case 0x02:  // QPACK encoder stream.
@@ -761,7 +796,7 @@
       // TODO(bnc): Create QPACK decoder stream.
       break;
     default:
-      SendStopSending(0x0D, id);
+      SendStopSending(0x0D, pending->id());
       return;
   }
 }
diff --git a/quic/core/http/quic_spdy_session.h b/quic/core/http/quic_spdy_session.h
index 1935a2f..43b4cb1 100644
--- a/quic/core/http/quic_spdy_session.h
+++ b/quic/core/http/quic_spdy_session.h
@@ -9,6 +9,22 @@
 #include <memory>
 #include <string>
 
+<<<<<<<
+|||||||
+#include "net/third_party/quic/core/http/quic_header_list.h"
+#include "net/third_party/quic/core/http/quic_headers_stream.h"
+#include "net/third_party/quic/core/http/quic_spdy_stream.h"
+#include "net/third_party/quic/core/qpack/qpack_decoder.h"
+#include "net/third_party/quic/core/qpack/qpack_decoder_stream_sender.h"
+=======
+#include "net/third_party/quic/core/http/quic_header_list.h"
+#include "net/third_party/quic/core/http/quic_headers_stream.h"
+#include "net/third_party/quic/core/http/quic_receive_control_stream.h"
+#include "net/third_party/quic/core/http/quic_send_control_stream.h"
+#include "net/third_party/quic/core/http/quic_spdy_stream.h"
+#include "net/third_party/quic/core/qpack/qpack_decoder.h"
+#include "net/third_party/quic/core/qpack/qpack_decoder_stream_sender.h"
+>>>>>>>
 #include "net/third_party/quiche/src/quic/core/http/quic_header_list.h"
 #include "net/third_party/quiche/src/quic/core/http/quic_headers_stream.h"
 #include "net/third_party/quiche/src/quic/core/http/quic_spdy_stream.h"
@@ -243,7 +259,7 @@
 
   // Creates HTTP/3 unidirectional stream of |id| and |type|. Sends
   // STOP_SENDING frame if |type| is not supported.
-  void CreateIncomingStreamFromPending(QuicStreamId id, uint64_t type);
+  void CreateIncomingStreamFromPending(PendingStream* pending, uint64_t type);
 
  private:
   friend class test::QuicSpdySessionPeer;
@@ -285,6 +301,10 @@
   // is deprecated.
   QuicHeadersStream* unowned_headers_stream_;
 
+  // HTTP/3 control streams.
+  QuicSendControlStream* send_control_stream_;
+  QuicReceiveControlStream* receive_control_stream_;
+
   // The maximum size of a header block that will be accepted from the peer,
   // defined per spec as key + value + overhead per field (uncompressed).
   size_t max_inbound_header_list_size_;
diff --git a/quic/core/http/quic_spdy_session_test.cc b/quic/core/http/quic_spdy_session_test.cc
index 1a33fd1..57c7e95 100644
--- a/quic/core/http/quic_spdy_session_test.cc
+++ b/quic/core/http/quic_spdy_session_test.cc
@@ -380,6 +380,13 @@
     return QuicUtils::StreamIdDelta(connection_->transport_version());
   }
 
+  std::string EncodeSettings(const SettingsFrame& settings) {
+    HttpEncoder encoder;
+    std::unique_ptr<char[]> buffer;
+    auto header_length = encoder.SerializeSettingsFrame(settings, &buffer);
+    return std::string(buffer.get(), header_length);
+  }
+
   QuicStreamId StreamCountToId(QuicStreamCount stream_count,
                                Perspective perspective,
                                bool bidirectional) {
@@ -420,7 +427,7 @@
   if (!VersionHasControlStreams(transport_version())) {
     return;
   }
-  EXPECT_FALSE(session_.UsesPendingStreams());
+  EXPECT_TRUE(session_.UsesPendingStreams());
 }
 
 TEST_P(QuicSpdySessionTestServer, PeerAddress) {
@@ -705,7 +712,7 @@
   MockPacketWriter* writer = static_cast<MockPacketWriter*>(
       QuicConnectionPeer::GetWriter(session_.connection()));
   EXPECT_CALL(*writer, WritePacket(_, _, _, _, _))
-      .WillOnce(Return(WriteResult(WRITE_STATUS_OK, 0)));
+      .WillRepeatedly(Return(WriteResult(WRITE_STATUS_OK, 0)));
   session_.GetMutableCryptoStream()->OnHandshakeMessage(msg);
 
   // Drive congestion control manually.
@@ -1622,7 +1629,7 @@
   if (!VersionHasControlStreams(transport_version())) {
     return;
   }
-  EXPECT_FALSE(session_.UsesPendingStreams());
+  EXPECT_TRUE(session_.UsesPendingStreams());
 }
 
 TEST_P(QuicSpdySessionTestClient, AvailableStreamsClient) {
@@ -1958,6 +1965,32 @@
   session_.ProcessPendingStream(&pending);
 }
 
+TEST_P(QuicSpdySessionTestServer, ReceiveControlStream) {
+  if (!VersionHasControlStreams(transport_version()) ||
+      !GetQuicReloadableFlag(quic_eliminate_static_stream_map_2)) {
+    return;
+  }
+  // Use a arbitrary stream id.
+  QuicStreamId stream_id =
+      GetNthClientInitiatedUnidirectionalStreamId(transport_version(), 3);
+  char type[] = {0x00};
+
+  QuicStreamFrame data1(stream_id, false, 0, QuicStringPiece(type, 1));
+  session_.OnStreamFrame(data1);
+  EXPECT_EQ(stream_id,
+            QuicSpdySessionPeer::GetReceiveControlStream(&session_)->id());
+
+  SettingsFrame settings;
+  settings.values[3] = 2;
+  settings.values[6] = 5;
+  std::string data = EncodeSettings(settings);
+  QuicStreamFrame frame(stream_id, false, 1, QuicStringPiece(data));
+
+  EXPECT_NE(5u, session_.max_inbound_header_list_size());
+  session_.OnStreamFrame(frame);
+  EXPECT_EQ(5u, session_.max_inbound_header_list_size());
+}
+
 }  // namespace
 }  // namespace test
 }  // namespace quic
diff --git a/quic/core/quic_connection.cc b/quic/core/quic_connection.cc
index a8672f5..558271a 100644
--- a/quic/core/quic_connection.cc
+++ b/quic/core/quic_connection.cc
@@ -376,8 +376,7 @@
   if (use_uber_received_packet_manager_) {
     QUIC_RELOADABLE_FLAG_COUNT(quic_use_uber_received_packet_manager);
   }
-  QUIC_DLOG(INFO) << ENDPOINT
-                  << "Created connection with server connection_id: "
+  QUIC_DLOG(INFO) << ENDPOINT << "Created connection with server connection ID "
                   << server_connection_id
                   << " and version: " << ParsedQuicVersionToString(version());
 
@@ -822,31 +821,55 @@
   QuicConnectionId server_connection_id =
       GetServerConnectionIdAsRecipient(header, perspective_);
 
-  if (server_connection_id == server_connection_id_ ||
-      HasIncomingConnectionId(server_connection_id)) {
-    return true;
-  }
+  if (server_connection_id != server_connection_id_ &&
+      !HasIncomingConnectionId(server_connection_id)) {
+    if (PacketCanReplaceConnectionId(header, perspective_)) {
+      QUIC_DLOG(INFO) << ENDPOINT << "Accepting packet with new connection ID "
+                      << server_connection_id << " instead of "
+                      << server_connection_id_;
+      return true;
+    }
 
-  if (PacketCanReplaceConnectionId(header, perspective_)) {
-    QUIC_DLOG(INFO) << ENDPOINT << "Accepting packet with new connection ID "
+    ++stats_.packets_dropped;
+    QUIC_DLOG(INFO) << ENDPOINT
+                    << "Ignoring packet from unexpected server connection ID "
                     << server_connection_id << " instead of "
                     << server_connection_id_;
+    QUIC_BUG << ENDPOINT
+             << "Ignoring packet from unexpected server connection ID "
+             << server_connection_id << " instead of " << server_connection_id_
+             << " header " << header;
+    if (debug_visitor_ != nullptr) {
+      debug_visitor_->OnIncorrectConnectionId(server_connection_id);
+    }
+    // If this is a server, the dispatcher routes each packet to the
+    // QuicConnection responsible for the packet's connection ID.  So if control
+    // arrives here and this is a server, the dispatcher must be malfunctioning.
+    DCHECK_NE(Perspective::IS_SERVER, perspective_);
+    return false;
+  }
+
+  if (!version().SupportsClientConnectionIds()) {
     return true;
   }
 
-  ++stats_.packets_dropped;
-  QUIC_DLOG(INFO) << ENDPOINT
-                  << "Ignoring packet from unexpected ConnectionId: "
-                  << server_connection_id << " instead of "
-                  << server_connection_id_;
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnIncorrectConnectionId(server_connection_id);
+  QuicConnectionId client_connection_id =
+      GetClientConnectionIdAsRecipient(header, perspective_);
+
+  if (client_connection_id != client_connection_id_) {
+    ++stats_.packets_dropped;
+    QUIC_DLOG(INFO) << ENDPOINT
+                    << "Ignoring packet from unexpected client connection ID "
+                    << client_connection_id << " instead of "
+                    << client_connection_id_;
+    QUIC_BUG << ENDPOINT
+             << "Ignoring packet from unexpected client connection ID "
+             << client_connection_id << " instead of " << client_connection_id_
+             << " header " << header;
+    return false;
   }
-  // If this is a server, the dispatcher routes each packet to the
-  // QuicConnection responsible for the packet's connection ID.  So if control
-  // arrives here and this is a server, the dispatcher must be malfunctioning.
-  DCHECK_NE(Perspective::IS_SERVER, perspective_);
-  return false;
+
+  return true;
 }
 
 bool QuicConnection::OnUnauthenticatedHeader(const QuicPacketHeader& header) {
@@ -2396,8 +2419,17 @@
   }
   ResetAckStates();
 
-  QUIC_DVLOG(1) << ENDPOINT << "Bundle an ACK opportunistically";
-  frames.push_back(GetUpdatedAckFrame());
+  QuicFrame updated_ack_frame = GetUpdatedAckFrame();
+  if (!updated_ack_frame.ack_frame->packets.Empty()) {
+    QUIC_DVLOG(1) << ENDPOINT << "Bundle an ACK opportunistically";
+    frames.push_back(updated_ack_frame);
+  } else {
+    QUIC_BUG << "Trying to opportunistically bundle ACK at "
+             << QuicUtils::EncryptionLevelToString(encryption_level_) << " "
+             << (has_pending_ack ? "" : "!")
+             << "has_pending_ack, stop_waiting_count_ " << stop_waiting_count_;
+  }
+
   if (!no_stop_waiting_frames_) {
     QuicStopWaitingFrame stop_waiting;
     PopulateStopWaitingFrame(&stop_waiting);
@@ -4022,7 +4054,9 @@
   }
   if (sent_packet_manager_.handshake_confirmed()) {
     // A forward secure packet has been received.
-    QUIC_BUG_IF(encryption_level_ != ENCRYPTION_FORWARD_SECURE);
+    QUIC_BUG_IF(encryption_level_ != ENCRYPTION_FORWARD_SECURE)
+        << "Unexpected connection close encryption level "
+        << QuicUtils::EncryptionLevelToString(encryption_level_);
     return ENCRYPTION_FORWARD_SECURE;
   }
   if (framer_.HasEncrypterOfEncryptionLevel(ENCRYPTION_ZERO_RTT)) {
@@ -4223,5 +4257,22 @@
   return received_packet_manager_.ack_frame();
 }
 
+void QuicConnection::set_client_connection_id(
+    QuicConnectionId client_connection_id) {
+  if (!version().SupportsClientConnectionIds()) {
+    QUIC_BUG_IF(!client_connection_id.IsEmpty())
+        << ENDPOINT << "Attempted to use client connection ID "
+        << client_connection_id << " with unsupported version " << version();
+    return;
+  }
+  client_connection_id_ = client_connection_id;
+  QUIC_DLOG(INFO) << ENDPOINT << "setting client connection ID to "
+                  << client_connection_id_
+                  << " for connection with server connection ID "
+                  << server_connection_id_;
+  packet_generator_.SetClientConnectionId(client_connection_id_);
+  framer_.SetExpectedClientConnectionIdLength(client_connection_id_.length());
+}
+
 #undef ENDPOINT  // undef for jumbo builds
 }  // namespace quic
diff --git a/quic/core/quic_connection.h b/quic/core/quic_connection.h
index b274266..00902a9 100644
--- a/quic/core/quic_connection.h
+++ b/quic/core/quic_connection.h
@@ -583,6 +583,10 @@
     return effective_peer_address_;
   }
   QuicConnectionId connection_id() const { return server_connection_id_; }
+  QuicConnectionId client_connection_id() const {
+    return client_connection_id_;
+  }
+  void set_client_connection_id(QuicConnectionId client_connection_id);
   const QuicClock* clock() const { return clock_; }
   QuicRandom* random_generator() const { return random_generator_; }
   QuicByteCount max_packet_length() const;
@@ -1169,6 +1173,7 @@
   QuicRandom* random_generator_;
 
   QuicConnectionId server_connection_id_;
+  QuicConnectionId client_connection_id_;
   // Address on the last successfully processed packet received from the
   // direct peer.
   QuicSocketAddress self_address_;
diff --git a/quic/core/quic_connection_test.cc b/quic/core/quic_connection_test.cc
index 0d09430..e4886b6 100644
--- a/quic/core/quic_connection_test.cc
+++ b/quic/core/quic_connection_test.cc
@@ -6877,7 +6877,8 @@
   // Send a version negotiation packet.
   std::unique_ptr<QuicEncryptedPacket> encrypted(
       peer_framer_.BuildVersionNegotiationPacket(
-          connection_id_, connection_.transport_version() > QUIC_VERSION_43,
+          connection_id_, EmptyQuicConnectionId(),
+          connection_.transport_version() > QUIC_VERSION_43,
           AllSupportedVersions()));
   std::unique_ptr<QuicReceivedPacket> received(
       ConstructReceivedPacket(*encrypted, QuicTime::Zero()));
@@ -6932,7 +6933,8 @@
                                  ConnectionCloseSource::FROM_SELF));
   std::unique_ptr<QuicEncryptedPacket> encrypted(
       framer_.BuildVersionNegotiationPacket(
-          connection_id_, connection_.transport_version() > QUIC_VERSION_43,
+          connection_id_, EmptyQuicConnectionId(),
+          connection_.transport_version() > QUIC_VERSION_43,
           AllSupportedVersions()));
   std::unique_ptr<QuicReceivedPacket> received(
       ConstructReceivedPacket(*encrypted, QuicTime::Zero()));
diff --git a/quic/core/quic_dispatcher.cc b/quic/core/quic_dispatcher.cc
index 049a63f..fa995da 100644
--- a/quic/core/quic_dispatcher.cc
+++ b/quic/core/quic_dispatcher.cc
@@ -19,9 +19,20 @@
 #include "net/third_party/quiche/src/quic/platform/api/quic_flag_utils.h"
 #include "net/third_party/quiche/src/quic/platform/api/quic_flags.h"
 #include "net/third_party/quiche/src/quic/platform/api/quic_logging.h"
+<<<<<<<
 #include "net/third_party/quiche/src/quic/platform/api/quic_ptr_util.h"
 #include "net/third_party/quiche/src/quic/platform/api/quic_stack_trace.h"
 #include "net/third_party/quiche/src/quic/platform/api/quic_string_piece.h"
+|||||||
+#include "net/third_party/quic/platform/api/quic_ptr_util.h"
+#include "net/third_party/quic/platform/api/quic_stack_trace.h"
+#include "net/third_party/quic/platform/api/quic_string_piece.h"
+=======
+#include "net/third_party/quic/platform/api/quic_ptr_util.h"
+#include "net/third_party/quic/platform/api/quic_stack_trace.h"
+#include "net/third_party/quic/platform/api/quic_string_piece.h"
+#include "net/third_party/quic/platform/api/quic_text_utils.h"
+>>>>>>>
 
 namespace quic {
 
@@ -287,7 +298,7 @@
     std::unique_ptr<QuicConnectionHelperInterface> helper,
     std::unique_ptr<QuicCryptoServerStream::Helper> session_helper,
     std::unique_ptr<QuicAlarmFactory> alarm_factory,
-    uint8_t expected_connection_id_length)
+    uint8_t expected_server_connection_id_length)
     : config_(config),
       crypto_config_(crypto_config),
       compressed_certs_cache_(
@@ -303,14 +314,15 @@
       framer_(GetSupportedVersions(),
               /*unused*/ QuicTime::Zero(),
               Perspective::IS_SERVER,
-              expected_connection_id_length),
+              expected_server_connection_id_length),
       last_error_(QUIC_NO_ERROR),
       new_sessions_allowed_per_event_loop_(0u),
       accept_new_connections_(true),
       allow_short_initial_server_connection_ids_(false),
       last_version_label_(0),
-      expected_connection_id_length_(expected_connection_id_length),
-      should_update_expected_connection_id_length_(false),
+      expected_server_connection_id_length_(
+          expected_server_connection_id_length),
+      should_update_expected_server_connection_id_length_(false),
       no_framer_(GetQuicRestartFlag(quic_no_framer_object_in_dispatcher)) {
   if (!no_framer_) {
     framer_.set_visitor(this);
@@ -331,6 +343,10 @@
 void QuicDispatcher::ProcessPacket(const QuicSocketAddress& self_address,
                                    const QuicSocketAddress& peer_address,
                                    const QuicReceivedPacket& packet) {
+  QUIC_DVLOG(2) << "Dispatcher received encrypted " << packet.length()
+                << " bytes:" << std::endl
+                << QuicTextUtils::HexDump(
+                       QuicStringPiece(packet.data(), packet.length()));
   current_self_address_ = self_address;
   current_peer_address_ = peer_address;
   // GetClientAddress must be called after current_peer_address_ is set.
@@ -347,12 +363,11 @@
   }
   QUIC_RESTART_FLAG_COUNT(quic_no_framer_object_in_dispatcher);
   QuicPacketHeader header;
-  uint8_t destination_connection_id_length;
   std::string detailed_error;
   const QuicErrorCode error = QuicFramer::ProcessPacketDispatcher(
-      packet, expected_connection_id_length_, &header.form,
+      packet, expected_server_connection_id_length_, &header.form,
       &header.version_flag, &last_version_label_,
-      &destination_connection_id_length, &header.destination_connection_id,
+      &header.destination_connection_id, &header.source_connection_id,
       &detailed_error);
   if (error != QUIC_NO_ERROR) {
     // Packet has framing error.
@@ -361,16 +376,18 @@
     return;
   }
   header.version = ParseQuicVersionLabel(last_version_label_);
-  if (destination_connection_id_length != expected_connection_id_length_ &&
-      !should_update_expected_connection_id_length_ &&
+  if (header.destination_connection_id.length() !=
+          expected_server_connection_id_length_ &&
+      !should_update_expected_server_connection_id_length_ &&
       !QuicUtils::VariableLengthConnectionIdAllowedForVersion(
           header.version.transport_version)) {
     SetLastError(QUIC_INVALID_PACKET_HEADER);
     QUIC_DLOG(ERROR) << "Invalid Connection Id Length";
     return;
   }
-  if (should_update_expected_connection_id_length_) {
-    expected_connection_id_length_ = destination_connection_id_length;
+  if (should_update_expected_server_connection_id_length_) {
+    expected_server_connection_id_length_ =
+        header.destination_connection_id.length();
   }
   // TODO(fayang): Instead of passing in QuicPacketHeader, pass format,
   // version_flag, version and destination_connection_id. Combine
@@ -387,10 +404,10 @@
 QuicConnectionId QuicDispatcher::MaybeReplaceServerConnectionId(
     QuicConnectionId server_connection_id,
     ParsedQuicVersion version) {
-  const uint8_t expected_connection_id_length =
-      no_framer_ ? expected_connection_id_length_
-                 : framer_.GetExpectedConnectionIdLength();
-  if (server_connection_id.length() == expected_connection_id_length) {
+  const uint8_t expected_server_connection_id_length =
+      no_framer_ ? expected_server_connection_id_length_
+                 : framer_.GetExpectedServerConnectionIdLength();
+  if (server_connection_id.length() == expected_server_connection_id_length) {
     return server_connection_id;
   }
   DCHECK(QuicUtils::VariableLengthConnectionIdAllowedForVersion(
@@ -402,7 +419,7 @@
   QuicConnectionId new_connection_id =
       session_helper_->GenerateConnectionIdForReject(version.transport_version,
                                                      server_connection_id);
-  DCHECK_EQ(expected_connection_id_length, new_connection_id.length());
+  DCHECK_EQ(expected_server_connection_id_length, new_connection_id.length());
   connection_id_map_.insert(
       std::make_pair(server_connection_id, new_connection_id));
   QUIC_DLOG(INFO) << "Replacing incoming connection ID " << server_connection_id
@@ -413,6 +430,7 @@
 bool QuicDispatcher::OnUnauthenticatedPublicHeader(
     const QuicPacketHeader& header) {
   current_server_connection_id_ = header.destination_connection_id;
+  current_client_connection_id_ = header.source_connection_id;
 
   // Port zero is only allowed for unidirectional UDP, so is disallowed by QUIC.
   // Given that we can't even send a reply rejecting the packet, just drop the
@@ -427,24 +445,25 @@
     return false;
   }
   QuicConnectionId server_connection_id = header.destination_connection_id;
+  QuicConnectionId client_connection_id = header.source_connection_id;
 
   // The IETF spec requires the client to generate an initial server
   // connection ID that is at least 64 bits long. After that initial
   // connection ID, the dispatcher picks a new one of its expected length.
   // Therefore we should never receive a connection ID that is smaller
   // than 64 bits and smaller than what we expect.
-  const uint8_t expected_connection_id_length =
-      no_framer_ ? expected_connection_id_length_
-                 : framer_.GetExpectedConnectionIdLength();
+  const uint8_t expected_server_connection_id_length =
+      no_framer_ ? expected_server_connection_id_length_
+                 : framer_.GetExpectedServerConnectionIdLength();
   if (server_connection_id.length() < kQuicMinimumInitialConnectionIdLength &&
-      server_connection_id.length() < expected_connection_id_length &&
+      server_connection_id.length() < expected_server_connection_id_length &&
       !allow_short_initial_server_connection_ids_) {
     DCHECK(header.version_flag);
     DCHECK(QuicUtils::VariableLengthConnectionIdAllowedForVersion(
         header.version.transport_version));
     QUIC_DLOG(INFO) << "Packet with short destination connection ID "
                     << server_connection_id << " expected "
-                    << static_cast<int>(expected_connection_id_length);
+                    << static_cast<int>(expected_server_connection_id_length);
     ProcessUnauthenticatedHeaderFate(kFateTimeWait, server_connection_id,
                                      header.form, header.version_flag,
                                      header.version);
@@ -517,9 +536,10 @@
         // Since the version is not supported, send a version negotiation
         // packet and stop processing the current packet.
         time_wait_list_manager()->SendVersionNegotiationPacket(
-            server_connection_id, header.form != GOOGLE_QUIC_PACKET,
-            GetSupportedVersions(), current_self_address_,
-            current_peer_address_, GetPerPacketContext());
+            server_connection_id, client_connection_id,
+            header.form != GOOGLE_QUIC_PACKET, GetSupportedVersions(),
+            current_self_address_, current_peer_address_,
+            GetPerPacketContext());
       }
       return false;
     }
@@ -891,7 +911,8 @@
   // with an empty version list, which can be understood by the client.
   std::vector<std::unique_ptr<QuicEncryptedPacket>> termination_packets;
   termination_packets.push_back(QuicFramer::BuildVersionNegotiationPacket(
-      server_connection_id, /*ietf_quic=*/format != GOOGLE_QUIC_PACKET,
+      server_connection_id, EmptyQuicConnectionId(),
+      /*ietf_quic=*/format != GOOGLE_QUIC_PACKET,
       ParsedQuicVersionVector{UnsupportedQuicVersion()}));
   if (format == GOOGLE_QUIC_PACKET) {
     QUIC_RELOADABLE_FLAG_COUNT_N(quic_terminate_gquic_connection_as_ietf, 2, 2);
@@ -1132,6 +1153,24 @@
     if (original_connection_id != server_connection_id) {
       session->connection()->AddIncomingConnectionId(original_connection_id);
     }
+    if (packet_list.version.SupportsClientConnectionIds()) {
+      // Parse out the first packet's source connection ID and set it as the
+      // connection's client connection ID.
+      QuicPacketHeader header;
+      QuicVersionLabel version_label;
+      std::string detailed_error;
+      const QuicErrorCode error = QuicFramer::ProcessPacketDispatcher(
+          *packets.front().packet, expected_server_connection_id_length_,
+          &header.form, &header.version_flag, &version_label,
+          &header.destination_connection_id, &header.source_connection_id,
+          &detailed_error);
+      if (error == QUIC_NO_ERROR) {
+        session->connection()->set_client_connection_id(
+            header.source_connection_id);
+      } else {
+        QUIC_DLOG(ERROR) << detailed_error;
+      }
+    }
     QUIC_DLOG(INFO) << "Created new session for " << server_connection_id;
     session_map_.insert(
         std::make_pair(server_connection_id, QuicWrapUnique(session)));
@@ -1236,6 +1275,10 @@
   if (original_connection_id != current_server_connection_id_) {
     session->connection()->AddIncomingConnectionId(original_connection_id);
   }
+  if (version.SupportsClientConnectionIds()) {
+    session->connection()->set_client_connection_id(
+        current_client_connection_id_);
+  }
   QUIC_DLOG(INFO) << "Created new session for "
                   << current_server_connection_id_;
   session_map_.insert(
diff --git a/quic/core/quic_dispatcher.h b/quic/core/quic_dispatcher.h
index 1798a0d..5e755dd 100644
--- a/quic/core/quic_dispatcher.h
+++ b/quic/core/quic_dispatcher.h
@@ -49,7 +49,7 @@
                  std::unique_ptr<QuicConnectionHelperInterface> helper,
                  std::unique_ptr<QuicCryptoServerStream::Helper> session_helper,
                  std::unique_ptr<QuicAlarmFactory> alarm_factory,
-                 uint8_t expected_connection_id_length);
+                 uint8_t expected_server_connection_id_length);
   QuicDispatcher(const QuicDispatcher&) = delete;
   QuicDispatcher& operator=(const QuicDispatcher&) = delete;
 
@@ -364,14 +364,14 @@
   // If true, our framer will change its expected connection ID length
   // to the received destination connection ID length of all IETF long headers.
   void SetShouldUpdateExpectedConnectionIdLength(
-      bool should_update_expected_connection_id_length) {
+      bool should_update_expected_server_connection_id_length) {
     if (!no_framer_) {
       framer_.SetShouldUpdateExpectedConnectionIdLength(
-          should_update_expected_connection_id_length);
+          should_update_expected_server_connection_id_length);
       return;
     }
-    should_update_expected_connection_id_length_ =
-        should_update_expected_connection_id_length;
+    should_update_expected_server_connection_id_length_ =
+        should_update_expected_server_connection_id_length;
   }
 
   // If true, the dispatcher will allow incoming initial packets that have
@@ -509,6 +509,7 @@
   // If |current_packet_| is a CHLO packet, the extracted alpn.
   std::string current_alpn_;
   QuicConnectionId current_server_connection_id_;
+  QuicConnectionId current_client_connection_id_;
 
   // Used to get the supported versions based on flag. Does not own.
   QuicVersionManager* version_manager_;
@@ -541,14 +542,15 @@
   // encode its length. This variable contains the length we expect to read.
   // This is also used to signal an error when a long header packet with
   // different destination connection ID length is received when
-  // should_update_expected_connection_id_length_ is false and packet's version
-  // does not allow variable length connection ID. Used when no_framer_ is true.
-  uint8_t expected_connection_id_length_;
+  // should_update_expected_server_connection_id_length_ is false and packet's
+  // version does not allow variable length connection ID. Used when no_framer_
+  // is true.
+  uint8_t expected_server_connection_id_length_;
 
-  // If true, change expected_connection_id_length_ to be the received
+  // If true, change expected_server_connection_id_length_ to be the received
   // destination connection ID length of all IETF long headers. Used when
   // no_framer_ is true.
-  bool should_update_expected_connection_id_length_;
+  bool should_update_expected_server_connection_id_length_;
 
   // Latched value of quic_no_framer_object_in_dispatcher.
   const bool no_framer_;
diff --git a/quic/core/quic_dispatcher_test.cc b/quic/core/quic_dispatcher_test.cc
index de06c52..668541b 100644
--- a/quic/core/quic_dispatcher_test.cc
+++ b/quic/core/quic_dispatcher_test.cc
@@ -493,7 +493,7 @@
 
   EXPECT_CALL(*dispatcher_, CreateQuicSession(_, _, _, _)).Times(0);
   EXPECT_CALL(*time_wait_list_manager_,
-              SendVersionNegotiationPacket(_, _, _, _, _, _))
+              SendVersionNegotiationPacket(_, _, _, _, _, _, _))
       .Times(1);
   QuicTransportVersion version =
       static_cast<QuicTransportVersion>(QuicTransportVersionMin() - 1);
@@ -512,7 +512,7 @@
 
   EXPECT_CALL(*dispatcher_, CreateQuicSession(_, _, _, _)).Times(0);
   EXPECT_CALL(*time_wait_list_manager_,
-              SendVersionNegotiationPacket(_, _, _, _, _, _))
+              SendVersionNegotiationPacket(_, _, _, _, _, _, _))
       .Times(0);
   QuicTransportVersion version =
       static_cast<QuicTransportVersion>(QuicTransportVersionMin() - 1);
@@ -538,7 +538,7 @@
 
   EXPECT_CALL(*dispatcher_, CreateQuicSession(_, _, _, _)).Times(0);
   EXPECT_CALL(*time_wait_list_manager_,
-              SendVersionNegotiationPacket(_, _, _, _, _, _))
+              SendVersionNegotiationPacket(_, _, _, _, _, _, _))
       .Times(1);
   QuicTransportVersion version =
       static_cast<QuicTransportVersion>(QuicTransportVersionMin() - 1);
diff --git a/quic/core/quic_framer.cc b/quic/core/quic_framer.cc
index eff8f49..c35c076 100644
--- a/quic/core/quic_framer.cc
+++ b/quic/core/quic_framer.cc
@@ -459,10 +459,11 @@
 QuicFramer::QuicFramer(const ParsedQuicVersionVector& supported_versions,
                        QuicTime creation_time,
                        Perspective perspective,
-                       uint8_t expected_connection_id_length)
+                       uint8_t expected_server_connection_id_length)
     : visitor_(nullptr),
       error_(QUIC_NO_ERROR),
       last_serialized_server_connection_id_(EmptyQuicConnectionId()),
+      last_serialized_client_connection_id_(EmptyQuicConnectionId()),
       last_version_label_(0),
       version_(PROTOCOL_UNSUPPORTED, QUIC_VERSION_UNSUPPORTED),
       supported_versions_(supported_versions),
@@ -478,8 +479,10 @@
       data_producer_(nullptr),
       infer_packet_header_type_from_version_(perspective ==
                                              Perspective::IS_CLIENT),
-      expected_connection_id_length_(expected_connection_id_length),
-      should_update_expected_connection_id_length_(false),
+      expected_server_connection_id_length_(
+          expected_server_connection_id_length),
+      expected_client_connection_id_length_(0),
+      should_update_expected_server_connection_id_length_(false),
       supports_multiple_packet_number_spaces_(false),
       last_written_packet_number_length_(0) {
   DCHECK(!supported_versions.empty());
@@ -1387,14 +1390,17 @@
 
 // static
 std::unique_ptr<QuicEncryptedPacket> QuicFramer::BuildVersionNegotiationPacket(
-    QuicConnectionId connection_id,
+    QuicConnectionId server_connection_id,
+    QuicConnectionId client_connection_id,
     bool ietf_quic,
     const ParsedQuicVersionVector& versions) {
   if (ietf_quic) {
-    return BuildIetfVersionNegotiationPacket(connection_id, versions);
+    return BuildIetfVersionNegotiationPacket(server_connection_id,
+                                             client_connection_id, versions);
   }
+  DCHECK(client_connection_id.IsEmpty());
   DCHECK(!versions.empty());
-  size_t len = kPublicFlagsSize + connection_id.length() +
+  size_t len = kPublicFlagsSize + server_connection_id.length() +
                versions.size() * kQuicVersionSize;
   std::unique_ptr<char[]> buffer(new char[len]);
   // Endianness is not a concern here, version negotiation packet does not have
@@ -1409,7 +1415,7 @@
     return nullptr;
   }
 
-  if (!writer.WriteConnectionId(connection_id)) {
+  if (!writer.WriteConnectionId(server_connection_id)) {
     return nullptr;
   }
 
@@ -1427,13 +1433,14 @@
 // static
 std::unique_ptr<QuicEncryptedPacket>
 QuicFramer::BuildIetfVersionNegotiationPacket(
-    QuicConnectionId source_connection_id,
+    QuicConnectionId server_connection_id,
+    QuicConnectionId client_connection_id,
     const ParsedQuicVersionVector& versions) {
   QUIC_DVLOG(1) << "Building IETF version negotiation packet: "
                 << ParsedQuicVersionVectorToString(versions);
   DCHECK(!versions.empty());
   size_t len = kPacketHeaderTypeSize + kConnectionIdLengthSize +
-               source_connection_id.length() +
+               client_connection_id.length() + server_connection_id.length() +
                (versions.size() + 1) * kQuicVersionSize;
   std::unique_ptr<char[]> buffer(new char[len]);
   QuicDataWriter writer(len, buffer.get());
@@ -1452,8 +1459,8 @@
     return nullptr;
   }
 
-  if (!AppendIetfConnectionIds(true, EmptyQuicConnectionId(),
-                               source_connection_id, &writer)) {
+  if (!AppendIetfConnectionIds(true, client_connection_id, server_connection_id,
+                               &writer)) {
     return nullptr;
   }
 
@@ -2195,6 +2202,9 @@
   }
 
   last_serialized_server_connection_id_ = server_connection_id;
+  if (version_.SupportsClientConnectionIds()) {
+    last_serialized_client_connection_id_ = GetClientConnectionIdAsSender(header, perspective_);
+  }
 
   if (QuicVersionHasLongHeaderLengths(transport_version()) &&
       header.version_flag) {
@@ -2521,11 +2531,15 @@
     // connection ID, and those received by server must include 8-byte
     // destination connection ID.
     header->destination_connection_id_included =
-        perspective_ == Perspective::IS_CLIENT ? CONNECTION_ID_ABSENT
-                                               : CONNECTION_ID_PRESENT;
+        (perspective_ == Perspective::IS_SERVER ||
+         version_.SupportsClientConnectionIds())
+            ? CONNECTION_ID_PRESENT
+            : CONNECTION_ID_ABSENT;
     header->source_connection_id_included =
-        perspective_ == Perspective::IS_CLIENT ? CONNECTION_ID_PRESENT
-                                               : CONNECTION_ID_ABSENT;
+        (perspective_ == Perspective::IS_CLIENT ||
+         version_.SupportsClientConnectionIds())
+            ? CONNECTION_ID_PRESENT
+            : CONNECTION_ID_ABSENT;
     // Read version tag.
     QuicVersionLabel version_label;
     if (!ProcessVersionLabel(reader, &version_label)) {
@@ -2580,8 +2594,10 @@
   // Connection ID length depends on the perspective. Client does not expect
   // destination connection ID, and server expects destination connection ID.
   header->destination_connection_id_included =
-      perspective_ == Perspective::IS_CLIENT ? CONNECTION_ID_ABSENT
-                                             : CONNECTION_ID_PRESENT;
+      (perspective_ == Perspective::IS_SERVER ||
+       version_.SupportsClientConnectionIds())
+          ? CONNECTION_ID_PRESENT
+          : CONNECTION_ID_ABSENT;
   header->source_connection_id_included = CONNECTION_ID_ABSENT;
   if (infer_packet_header_type_from_version_ &&
       transport_version() > QUIC_VERSION_44 && !(type & FLAGS_FIXED_BIT)) {
@@ -2614,11 +2630,21 @@
 bool QuicFramer::ProcessAndValidateIetfConnectionIdLength(
     QuicDataReader* reader,
     ParsedQuicVersion version,
-    bool should_update_expected_connection_id_length,
-    uint8_t* expected_connection_id_length,
+    Perspective perspective,
+    bool should_update_expected_server_connection_id_length,
+    uint8_t* expected_server_connection_id_length,
     uint8_t* destination_connection_id_length,
     uint8_t* source_connection_id_length,
     std::string* detailed_error) {
+  QUIC_LOG(ERROR) << "ds33 should_update_expected_server_connection_id_length "
+                  << (should_update_expected_server_connection_id_length ? "Y"
+                                                                         : "N")
+                  << " expected_server_connection_id_length "
+                  << (int)*expected_server_connection_id_length
+                  << " destination_connection_id_length "
+                  << (int)*destination_connection_id_length
+                  << " source_connection_id_length "
+                  << (int)*source_connection_id_length;
   uint8_t connection_id_lengths_byte;
   if (!reader->ReadBytes(&connection_id_lengths_byte, 1)) {
     *detailed_error = "Unable to read ConnectionId length.";
@@ -2629,18 +2655,21 @@
   if (dcil != 0) {
     dcil += kConnectionIdLengthAdjustment;
   }
-  if (should_update_expected_connection_id_length &&
-      *expected_connection_id_length != dcil) {
-    QUIC_DVLOG(1) << "Updating expected_connection_id_length: "
-                  << static_cast<int>(*expected_connection_id_length) << " -> "
-                  << static_cast<int>(dcil);
-    *expected_connection_id_length = dcil;
-  }
   uint8_t scil = connection_id_lengths_byte & kSourceConnectionIdLengthMask;
   if (scil != 0) {
     scil += kConnectionIdLengthAdjustment;
   }
-  if (!should_update_expected_connection_id_length &&
+  if (should_update_expected_server_connection_id_length) {
+    uint8_t server_connection_id_length =
+        perspective == Perspective::IS_SERVER ? dcil : scil;
+    if (*expected_server_connection_id_length != server_connection_id_length) {
+      QUIC_DVLOG(1) << "Updating expected_server_connection_id_length: "
+                    << static_cast<int>(*expected_server_connection_id_length)
+                    << " -> " << static_cast<int>(server_connection_id_length);
+      *expected_server_connection_id_length = server_connection_id_length;
+    }
+  }
+  if (!should_update_expected_server_connection_id_length &&
       (dcil != *destination_connection_id_length ||
        scil != *source_connection_id_length) &&
       !QuicUtils::VariableLengthConnectionIdAllowedForVersion(
@@ -2665,18 +2694,35 @@
 
   uint8_t destination_connection_id_length =
       header->destination_connection_id_included == CONNECTION_ID_PRESENT
-          ? expected_connection_id_length_
+          ? (perspective_ == Perspective::IS_SERVER
+                 ? expected_server_connection_id_length_
+                 : expected_client_connection_id_length_)
           : 0;
   uint8_t source_connection_id_length =
       header->source_connection_id_included == CONNECTION_ID_PRESENT
-          ? expected_connection_id_length_
+          ? (perspective_ == Perspective::IS_CLIENT
+                 ? expected_server_connection_id_length_
+                 : expected_client_connection_id_length_)
           : 0;
+  QUIC_LOG(ERROR) << ENDPOINT
+                  << "ds33 should_update_expected_server_connection_id_length_ "
+                  << (should_update_expected_server_connection_id_length_ ? "Y"
+                                                                          : "N")
+                  << " expected_server_connection_id_length_ "
+                  << (int)expected_server_connection_id_length_
+                  << " expected_client_connection_id_length_ "
+                  << (int)expected_client_connection_id_length_
+                  << " destination_connection_id_length "
+                  << (int)destination_connection_id_length
+                  << " source_connection_id_length "
+                  << (int)source_connection_id_length << " header " << *header;
   if (header->form == IETF_QUIC_LONG_HEADER_PACKET) {
     if (!ProcessAndValidateIetfConnectionIdLength(
-            reader, header->version,
-            should_update_expected_connection_id_length_,
-            &expected_connection_id_length_, &destination_connection_id_length,
-            &source_connection_id_length, &detailed_error_)) {
+            reader, header->version, perspective_,
+            should_update_expected_server_connection_id_length_,
+            &expected_server_connection_id_length_,
+            &destination_connection_id_length, &source_connection_id_length,
+            &detailed_error_)) {
       return false;
     }
   }
@@ -2715,7 +2761,11 @@
     QUIC_RESTART_FLAG_COUNT_N(quic_do_not_override_connection_id, 5, 5);
     if (header->source_connection_id_included == CONNECTION_ID_ABSENT) {
       DCHECK_EQ(EmptyQuicConnectionId(), header->source_connection_id);
-      header->source_connection_id = last_serialized_server_connection_id_;
+      if (perspective_ == Perspective::IS_CLIENT) {
+        header->source_connection_id = last_serialized_server_connection_id_;
+      } else {
+        header->source_connection_id = last_serialized_client_connection_id_;
+      }
     }
   }
 
@@ -6042,28 +6092,30 @@
 // static
 QuicErrorCode QuicFramer::ProcessPacketDispatcher(
     const QuicEncryptedPacket& packet,
-    uint8_t expected_connection_id_length,
+    uint8_t expected_server_connection_id_length,
     PacketHeaderFormat* format,
     bool* version_flag,
     QuicVersionLabel* version_label,
-    uint8_t* destination_connection_id_length,
     QuicConnectionId* destination_connection_id,
+    QuicConnectionId* source_connection_id,
     std::string* detailed_error) {
   QuicDataReader reader(packet.data(), packet.length());
 
+  *source_connection_id = EmptyQuicConnectionId();
   uint8_t first_byte;
   if (!reader.ReadBytes(&first_byte, 1)) {
     *detailed_error = "Unable to read first byte.";
     return QUIC_INVALID_PACKET_HEADER;
   }
+  uint8_t destination_connection_id_length = 0, source_connection_id_length = 0;
   if (!QuicUtils::IsIetfPacketHeader(first_byte)) {
     *format = GOOGLE_QUIC_PACKET;
     *version_flag = (first_byte & PACKET_PUBLIC_FLAGS_VERSION) != 0;
-    *destination_connection_id_length =
+    destination_connection_id_length =
         first_byte & PACKET_PUBLIC_FLAGS_8BYTE_CONNECTION_ID;
-    if (*destination_connection_id_length == 0 ||
+    if (destination_connection_id_length == 0 ||
         !reader.ReadConnectionId(destination_connection_id,
-                                 *destination_connection_id_length)) {
+                                 destination_connection_id_length)) {
       *detailed_error = "Unable to read ConnectionId.";
       return QUIC_INVALID_PACKET_HEADER;
     }
@@ -6083,27 +6135,33 @@
       *detailed_error = "Unable to read protocol version.";
       return QUIC_INVALID_PACKET_HEADER;
     }
-    // Set should_update_expected_connection_id_length to true to bypass
+    // Set should_update_expected_server_connection_id_length to true to bypass
     // connection ID lengths validation.
-    uint8_t unused_source_connection_id_length = 0;
-    uint8_t unused_expected_connection_id_length = 0;
+    uint8_t unused_expected_server_connection_id_length = 0;
     if (!ProcessAndValidateIetfConnectionIdLength(
             &reader, ParseQuicVersionLabel(*version_label),
-            /*should_update_expected_connection_id_length=*/true,
-            &unused_expected_connection_id_length,
-            destination_connection_id_length,
-            &unused_source_connection_id_length, detailed_error)) {
+            Perspective::IS_SERVER,
+            /*should_update_expected_server_connection_id_length=*/true,
+            &unused_expected_server_connection_id_length,
+            &destination_connection_id_length, &source_connection_id_length,
+            detailed_error)) {
       return QUIC_INVALID_PACKET_HEADER;
     }
   } else {
-    // For short header packets, expected_connection_id_length is used to
+    // For short header packets, expected_server_connection_id_length is used to
     // determine the destination_connection_id_length.
-    *destination_connection_id_length = expected_connection_id_length;
+    destination_connection_id_length = expected_server_connection_id_length;
   }
   // Read destination connection ID.
   if (!reader.ReadConnectionId(destination_connection_id,
-                               *destination_connection_id_length)) {
-    *detailed_error = "Unable to read Destination ConnectionId.";
+                               destination_connection_id_length)) {
+    *detailed_error = "Unable to read destination connection ID.";
+    return QUIC_INVALID_PACKET_HEADER;
+  }
+  // Read source connection ID.
+  if (!reader.ReadConnectionId(source_connection_id,
+                               source_connection_id_length)) {
+    *detailed_error = "Unable to read source connection ID.";
     return QUIC_INVALID_PACKET_HEADER;
   }
   return QUIC_NO_ERROR;
@@ -6234,13 +6292,14 @@
     *detailed_error = "Packet is not a version negotiation packet";
     return false;
   }
-  uint8_t expected_connection_id_length = 0,
+  uint8_t expected_server_connection_id_length = 0,
           destination_connection_id_length = 0, source_connection_id_length = 0;
   if (!ProcessAndValidateIetfConnectionIdLength(
-          &reader, UnsupportedQuicVersion(),
-          /*should_update_expected_connection_id_length=*/true,
-          &expected_connection_id_length, &destination_connection_id_length,
-          &source_connection_id_length, detailed_error)) {
+          &reader, UnsupportedQuicVersion(), Perspective::IS_CLIENT,
+          /*should_update_expected_server_connection_id_length=*/true,
+          &expected_server_connection_id_length,
+          &destination_connection_id_length, &source_connection_id_length,
+          detailed_error)) {
     return false;
   }
   if (destination_connection_id_length != 0) {
diff --git a/quic/core/quic_framer.h b/quic/core/quic_framer.h
index e56aba2..931dd4a 100644
--- a/quic/core/quic_framer.h
+++ b/quic/core/quic_framer.h
@@ -226,7 +226,7 @@
   QuicFramer(const ParsedQuicVersionVector& supported_versions,
              QuicTime creation_time,
              Perspective perspective,
-             uint8_t expected_connection_id_length);
+             uint8_t expected_server_connection_id_length);
   QuicFramer(const QuicFramer&) = delete;
   QuicFramer& operator=(const QuicFramer&) = delete;
 
@@ -374,18 +374,18 @@
       QuicVariableLengthIntegerLength length_length);
 
   // Lightweight parsing of |packet| and populates |format|, |version_flag|,
-  // |version_label|, |destination_connection_id_length|,
-  // |destination_connection_id| and |detailed_error|. Please note,
-  // |expected_connection_id_length| is only used to determine IETF short header
-  // packet's destination connection ID length.
+  // |version_label|, |destination_connection_id|, |source_connection_id| and
+  // |detailed_error|. Please note, |expected_server_connection_id_length| is
+  // only used to determine IETF short header packet's destination connection ID
+  // length.
   static QuicErrorCode ProcessPacketDispatcher(
       const QuicEncryptedPacket& packet,
-      uint8_t expected_connection_id_length,
+      uint8_t expected_server_connection_id_length,
       PacketHeaderFormat* format,
       bool* version_flag,
       QuicVersionLabel* version_label,
-      uint8_t* destination_connection_id_length,
       QuicConnectionId* destination_connection_id,
+      QuicConnectionId* source_connection_id,
       std::string* detailed_error);
 
   // Serializes a packet containing |frames| into |buffer|.
@@ -435,13 +435,15 @@
 
   // Returns a new version negotiation packet.
   static std::unique_ptr<QuicEncryptedPacket> BuildVersionNegotiationPacket(
-      QuicConnectionId connection_id,
+      QuicConnectionId server_connection_id,
+      QuicConnectionId client_connection_id,
       bool ietf_quic,
       const ParsedQuicVersionVector& versions);
 
   // Returns a new IETF version negotiation packet.
   static std::unique_ptr<QuicEncryptedPacket> BuildIetfVersionNegotiationPacket(
-      QuicConnectionId source_connection_id,
+      QuicConnectionId server_connection_id,
+      QuicConnectionId client_connection_id,
       const ParsedQuicVersionVector& versions);
 
   // If header.version_flag is set, the version in the
@@ -576,14 +578,23 @@
   // If true, QuicFramer will change its expected connection ID length
   // to the received destination connection ID length of all IETF long headers.
   void SetShouldUpdateExpectedConnectionIdLength(
-      bool should_update_expected_connection_id_length) {
-    should_update_expected_connection_id_length_ =
-        should_update_expected_connection_id_length;
+      bool should_update_expected_server_connection_id_length) {
+    should_update_expected_server_connection_id_length_ =
+        should_update_expected_server_connection_id_length;
   }
 
-  // The connection ID length the framer expects on incoming IETF short headers.
-  uint8_t GetExpectedConnectionIdLength() {
-    return expected_connection_id_length_;
+  // The connection ID length the framer expects on incoming IETF short headers
+  // on the server.
+  uint8_t GetExpectedServerConnectionIdLength() {
+    return expected_server_connection_id_length_;
+  }
+
+  // Change the expected destination connection ID length for short headers on
+  // the client.
+  void SetExpectedClientConnectionIdLength(
+      uint8_t expected_client_connection_id_length) {
+    expected_client_connection_id_length_ =
+        expected_client_connection_id_length;
   }
 
   void EnableMultiplePacketNumberSpacesSupport();
@@ -715,8 +726,9 @@
   static bool ProcessAndValidateIetfConnectionIdLength(
       QuicDataReader* reader,
       ParsedQuicVersion version,
-      bool should_update_expected_connection_id_length,
-      uint8_t* expected_connection_id_length,
+      Perspective perspective,
+      bool should_update_expected_server_connection_id_length,
+      uint8_t* expected_server_connection_id_length,
       uint8_t* destination_connection_id_length,
       uint8_t* source_connection_id_length,
       std::string* detailed_error);
@@ -960,6 +972,8 @@
   QuicPacketNumber largest_decrypted_packet_numbers_[NUM_PACKET_NUMBER_SPACES];
   // Last server connection ID seen on the wire.
   QuicConnectionId last_serialized_server_connection_id_;
+  // Last client connection ID seen on the wire.
+  QuicConnectionId last_serialized_client_connection_id_;
   // The last QUIC version label received.
   // TODO(fayang): Remove this when deprecating
   // quic_no_framer_object_in_dispatcher.
@@ -1014,18 +1028,18 @@
   bool infer_packet_header_type_from_version_;
 
   // IETF short headers contain a destination connection ID but do not
-  // encode its length. This variable contains the length we expect to read.
-  // This is also used to validate the long header connection ID lengths in
-  // older versions of QUIC.
-  // TODO(fayang): Remove this when deprecating
-  // quic_no_framer_object_in_dispatcher.
-  uint8_t expected_connection_id_length_;
+  // encode its length. These variables contains the length we expect to read.
+  // This is also used to validate the long header destination connection ID
+  // lengths in older versions of QUIC.
+  uint8_t expected_server_connection_id_length_;
+  uint8_t expected_client_connection_id_length_;
 
-  // When this is true, QuicFramer will change expected_connection_id_length_
-  // to the received destination connection ID length of all IETF long headers.
+  // When this is true, QuicFramer will change
+  // expected_server_connection_id_length_ to the received destination
+  // connection ID length of all IETF long headers.
   // TODO(fayang): Remove this when deprecating
   // quic_no_framer_object_in_dispatcher.
-  bool should_update_expected_connection_id_length_;
+  bool should_update_expected_server_connection_id_length_;
 
   // Indicates whether this framer supports multiple packet number spaces.
   bool supports_multiple_packet_number_spaces_;
diff --git a/quic/core/quic_framer_test.cc b/quic/core/quic_framer_test.cc
index 85af7ea..5f46e8e 100644
--- a/quic/core/quic_framer_test.cc
+++ b/quic/core/quic_framer_test.cc
@@ -916,18 +916,17 @@
 
   PacketHeaderFormat format;
   bool version_flag;
-  uint8_t destination_connection_id_length;
-  QuicConnectionId destination_connection_id;
+  QuicConnectionId destination_connection_id, source_connection_id;
   QuicVersionLabel version_label;
   std::string detailed_error;
-  EXPECT_EQ(QUIC_NO_ERROR, QuicFramer::ProcessPacketDispatcher(
-                               *encrypted, kQuicDefaultConnectionIdLength,
-                               &format, &version_flag, &version_label,
-                               &destination_connection_id_length,
-                               &destination_connection_id, &detailed_error));
+  EXPECT_EQ(QUIC_NO_ERROR,
+            QuicFramer::ProcessPacketDispatcher(
+                *encrypted, kQuicDefaultConnectionIdLength, &format,
+                &version_flag, &version_label, &destination_connection_id,
+                &source_connection_id, &detailed_error));
   EXPECT_EQ(GOOGLE_QUIC_PACKET, format);
   EXPECT_FALSE(version_flag);
-  EXPECT_EQ(kQuicDefaultConnectionIdLength, destination_connection_id_length);
+  EXPECT_EQ(kQuicDefaultConnectionIdLength, destination_connection_id.length());
   EXPECT_EQ(FramerTestConnectionId(), destination_connection_id);
 }
 
@@ -994,18 +993,17 @@
 
   PacketHeaderFormat format;
   bool version_flag;
-  uint8_t destination_connection_id_length;
-  QuicConnectionId destination_connection_id;
+  QuicConnectionId destination_connection_id, source_connection_id;
   QuicVersionLabel version_label;
   std::string detailed_error;
-  EXPECT_EQ(QUIC_NO_ERROR, QuicFramer::ProcessPacketDispatcher(
-                               *encrypted, kQuicDefaultConnectionIdLength,
-                               &format, &version_flag, &version_label,
-                               &destination_connection_id_length,
-                               &destination_connection_id, &detailed_error));
+  EXPECT_EQ(QUIC_NO_ERROR,
+            QuicFramer::ProcessPacketDispatcher(
+                *encrypted, kQuicDefaultConnectionIdLength, &format,
+                &version_flag, &version_label, &destination_connection_id,
+                &source_connection_id, &detailed_error));
   EXPECT_EQ(IETF_QUIC_LONG_HEADER_PACKET, format);
   EXPECT_TRUE(version_flag);
-  EXPECT_EQ(kQuicDefaultConnectionIdLength, destination_connection_id_length);
+  EXPECT_EQ(kQuicDefaultConnectionIdLength, destination_connection_id.length());
   EXPECT_EQ(FramerTestConnectionId(), destination_connection_id);
 }
 
@@ -6626,7 +6624,8 @@
   QuicConnectionId connection_id = FramerTestConnectionId();
   std::unique_ptr<QuicEncryptedPacket> data(
       framer_.BuildVersionNegotiationPacket(
-          connection_id, framer_.transport_version() > QUIC_VERSION_43,
+          connection_id, EmptyQuicConnectionId(),
+          framer_.transport_version() > QUIC_VERSION_43,
           SupportedVersions(GetParam())));
   test::CompareCharArraysWithHexError("constructed packet", data->data(),
                                       data->length(), AsChars(p), p_size);
@@ -13182,8 +13181,8 @@
   QuicConnectionId connection_id(connection_id_bytes,
                                  sizeof(connection_id_bytes));
   QuicFramerPeer::SetLargestPacketNumber(&framer_, kPacketNumber - 2);
-  QuicFramerPeer::SetExpectedConnectionIDLength(&framer_,
-                                                connection_id.length());
+  QuicFramerPeer::SetExpectedServerConnectionIDLength(&framer_,
+                                                      connection_id.length());
 
   // clang-format off
   PacketFragments packet = {
@@ -13320,8 +13319,7 @@
 
   PacketHeaderFormat format;
   bool version_flag;
-  uint8_t destination_connection_id_length;
-  QuicConnectionId destination_connection_id;
+  QuicConnectionId destination_connection_id, source_connection_id;
   QuicVersionLabel version_label;
   std::string detailed_error;
   EXPECT_EQ(QUIC_NO_ERROR,
@@ -13329,21 +13327,21 @@
                 QuicEncryptedPacket(AsChars(long_header_packet),
                                     QUIC_ARRAYSIZE(long_header_packet)),
                 kQuicDefaultConnectionIdLength, &format, &version_flag,
-                &version_label, &destination_connection_id_length,
-                &destination_connection_id, &detailed_error));
+                &version_label, &destination_connection_id,
+                &source_connection_id, &detailed_error));
   EXPECT_EQ(IETF_QUIC_LONG_HEADER_PACKET, format);
   EXPECT_TRUE(version_flag);
-  EXPECT_EQ(9, destination_connection_id_length);
+  EXPECT_EQ(9, destination_connection_id.length());
   EXPECT_EQ(FramerTestConnectionIdNineBytes(), destination_connection_id);
 
-  EXPECT_EQ(QUIC_NO_ERROR,
-            QuicFramer::ProcessPacketDispatcher(
-                short_header_encrypted, 9, &format, &version_flag,
-                &version_label, &destination_connection_id_length,
-                &destination_connection_id, &detailed_error));
+  EXPECT_EQ(
+      QUIC_NO_ERROR,
+      QuicFramer::ProcessPacketDispatcher(
+          short_header_encrypted, 9, &format, &version_flag, &version_label,
+          &destination_connection_id, &source_connection_id, &detailed_error));
   EXPECT_EQ(IETF_QUIC_SHORT_HEADER_PACKET, format);
   EXPECT_FALSE(version_flag);
-  EXPECT_EQ(9, destination_connection_id_length);
+  EXPECT_EQ(9, destination_connection_id.length());
   EXPECT_EQ(FramerTestConnectionIdNineBytes(), destination_connection_id);
 }
 
diff --git a/quic/core/quic_packet_creator.cc b/quic/core/quic_packet_creator.cc
index e69ac85..fbc21a8 100644
--- a/quic/core/quic_packet_creator.cc
+++ b/quic/core/quic_packet_creator.cc
@@ -75,6 +75,7 @@
       server_connection_id_included_(CONNECTION_ID_PRESENT),
       packet_size_(0),
       server_connection_id_(server_connection_id),
+      client_connection_id_(EmptyQuicConnectionId()),
       packet_(QuicPacketNumber(),
               PACKET_1BYTE_PACKET_NUMBER,
               nullptr,
@@ -627,6 +628,7 @@
   DCHECK_EQ(Perspective::IS_SERVER, framer_->perspective());
   std::unique_ptr<QuicEncryptedPacket> encrypted =
       QuicFramer::BuildVersionNegotiationPacket(server_connection_id_,
+                                                client_connection_id_,
                                                 ietf_quic, supported_versions);
   DCHECK(encrypted);
   DCHECK_GE(max_packet_length_, encrypted->length());
@@ -741,7 +743,7 @@
   }
   QUIC_RESTART_FLAG_COUNT_N(quic_do_not_override_connection_id, 1, 5);
   if (framer_->perspective() == Perspective::IS_SERVER) {
-    return EmptyQuicConnectionId();
+    return client_connection_id_;
   }
   return server_connection_id_;
 }
@@ -752,7 +754,7 @@
   }
   QUIC_RESTART_FLAG_COUNT_N(quic_do_not_override_connection_id, 6, 6);
   if (framer_->perspective() == Perspective::IS_CLIENT) {
-    return EmptyQuicConnectionId();
+    return client_connection_id_;
   }
   return server_connection_id_;
 }
@@ -763,7 +765,8 @@
       GetQuicRestartFlag(quic_do_not_override_connection_id)) {
     // Packets sent by client always include destination connection ID, and
     // those sent by the server do not include destination connection ID.
-    return framer_->perspective() == Perspective::IS_CLIENT
+    return (framer_->perspective() == Perspective::IS_CLIENT ||
+            framer_->version().SupportsClientConnectionIds())
                ? CONNECTION_ID_PRESENT
                : CONNECTION_ID_ABSENT;
   }
@@ -773,7 +776,9 @@
 QuicConnectionIdIncluded QuicPacketCreator::GetSourceConnectionIdIncluded()
     const {
   // Long header packets sent by server include source connection ID.
-  if (HasIetfLongHeader() && framer_->perspective() == Perspective::IS_SERVER) {
+  if (HasIetfLongHeader() &&
+      (framer_->perspective() == Perspective::IS_SERVER ||
+       framer_->version().SupportsClientConnectionIds())) {
     return CONNECTION_ID_PRESENT;
   }
   if (GetQuicRestartFlag(quic_do_not_override_connection_id) &&
@@ -1038,6 +1043,13 @@
   server_connection_id_ = server_connection_id;
 }
 
+void QuicPacketCreator::SetClientConnectionId(
+    QuicConnectionId client_connection_id) {
+  DCHECK(client_connection_id.IsEmpty() ||
+         framer_->version().SupportsClientConnectionIds());
+  client_connection_id_ = client_connection_id;
+}
+
 void QuicPacketCreator::SetTransmissionType(TransmissionType type) {
   DCHECK(can_set_transmission_type_);
 
diff --git a/quic/core/quic_packet_creator.h b/quic/core/quic_packet_creator.h
index 259b577..b666f71 100644
--- a/quic/core/quic_packet_creator.h
+++ b/quic/core/quic_packet_creator.h
@@ -226,9 +226,12 @@
   void SetServerConnectionIdIncluded(
       QuicConnectionIdIncluded server_connection_id_included);
 
-  // Update the connection ID used in outgoing packets.
+  // Update the server connection ID used in outgoing packets.
   void SetServerConnectionId(QuicConnectionId server_connection_id);
 
+  // Update the client connection ID used in outgoing packets.
+  void SetClientConnectionId(QuicConnectionId client_connection_id);
+
   // Sets the encryption level that will be applied to new packets.
   void set_encryption_level(EncryptionLevel level) {
     packet_.encryption_level = level;
@@ -405,6 +408,7 @@
   // QuicEncryptedPacket has been flattened into SerializedPacket.
   size_t packet_size_;
   QuicConnectionId server_connection_id_;
+  QuicConnectionId client_connection_id_;
 
   // Packet used to invoke OnSerializedPacket.
   SerializedPacket packet_;
diff --git a/quic/core/quic_packet_generator.cc b/quic/core/quic_packet_generator.cc
index f490900..766f8ca 100644
--- a/quic/core/quic_packet_generator.cc
+++ b/quic/core/quic_packet_generator.cc
@@ -574,4 +574,9 @@
   packet_creator_.SetServerConnectionId(server_connection_id);
 }
 
+void QuicPacketGenerator::SetClientConnectionId(
+    QuicConnectionId client_connection_id) {
+  packet_creator_.SetClientConnectionId(client_connection_id);
+}
+
 }  // namespace quic
diff --git a/quic/core/quic_packet_generator.h b/quic/core/quic_packet_generator.h
index 6ea8215..ec25550 100644
--- a/quic/core/quic_packet_generator.h
+++ b/quic/core/quic_packet_generator.h
@@ -238,6 +238,9 @@
   // Update the server connection ID used in outgoing packets.
   void SetServerConnectionId(QuicConnectionId server_connection_id);
 
+  // Update the client connection ID used in outgoing packets.
+  void SetClientConnectionId(QuicConnectionId client_connection_id);
+
   void set_debug_delegate(QuicPacketCreator::DebugDelegate* debug_delegate) {
     packet_creator_.set_debug_delegate(debug_delegate);
   }
diff --git a/quic/core/quic_packets.cc b/quic/core/quic_packets.cc
index 57bda54..738cc6e 100644
--- a/quic/core/quic_packets.cc
+++ b/quic/core/quic_packets.cc
@@ -27,6 +27,16 @@
   return header.source_connection_id;
 }
 
+QuicConnectionId GetClientConnectionIdAsRecipient(
+    const QuicPacketHeader& header,
+    Perspective perspective) {
+  DCHECK(GetQuicRestartFlag(quic_do_not_override_connection_id));
+  if (perspective == Perspective::IS_CLIENT) {
+    return header.destination_connection_id;
+  }
+  return header.source_connection_id;
+}
+
 QuicConnectionId GetServerConnectionIdAsSender(const QuicPacketHeader& header,
                                                Perspective perspective) {
   if (perspective == Perspective::IS_CLIENT ||
@@ -48,6 +58,16 @@
   return header.source_connection_id_included;
 }
 
+QuicConnectionId GetClientConnectionIdAsSender(const QuicPacketHeader& header,
+                                               Perspective perspective) {
+  if (perspective == Perspective::IS_CLIENT ||
+      !GetQuicRestartFlag(quic_do_not_override_connection_id)) {
+    return header.source_connection_id;
+  }
+  QUIC_RESTART_FLAG_COUNT_N(quic_do_not_override_connection_id, 3, 5);
+  return header.destination_connection_id;
+}
+
 QuicConnectionIdIncluded GetClientConnectionIdIncludedAsSender(
     const QuicPacketHeader& header,
     Perspective perspective) {
diff --git a/quic/core/quic_packets.h b/quic/core/quic_packets.h
index d3c2600..b1964e7 100644
--- a/quic/core/quic_packets.h
+++ b/quic/core/quic_packets.h
@@ -41,6 +41,12 @@
 // Returns the destination connection ID of |header| when |perspective| is
 // client, and the source connection ID when |perspective| is server.
 QUIC_EXPORT_PRIVATE QuicConnectionId
+GetClientConnectionIdAsRecipient(const QuicPacketHeader& header,
+                                 Perspective perspective);
+
+// Returns the destination connection ID of |header| when |perspective| is
+// client, and the source connection ID when |perspective| is server.
+QUIC_EXPORT_PRIVATE QuicConnectionId
 GetServerConnectionIdAsSender(const QuicPacketHeader& header,
                               Perspective perspective);
 
@@ -51,6 +57,12 @@
 GetServerConnectionIdIncludedAsSender(const QuicPacketHeader& header,
                                       Perspective perspective);
 
+// Returns the destination connection ID of |header| when |perspective| is
+// server, and the source connection ID when |perspective| is client.
+QUIC_EXPORT_PRIVATE QuicConnectionId
+GetClientConnectionIdAsSender(const QuicPacketHeader& header,
+                              Perspective perspective);
+
 // Returns the destination connection ID included of |header| when |perspective|
 // is server, and the source connection ID included when |perspective| is
 // client.
diff --git a/quic/core/quic_session.h b/quic/core/quic_session.h
index 5e527f3..a48446f 100644
--- a/quic/core/quic_session.h
+++ b/quic/core/quic_session.h
@@ -506,6 +506,8 @@
     return dynamic_stream_map_;
   }
 
+  PendingStreamMap& pending_streams() { return pending_stream_map_; }
+
   ClosedStreams* closed_streams() { return &closed_streams_; }
 
   const ZombieStreamMap& zombie_streams() const { return zombie_streams_; }
diff --git a/quic/core/quic_time_wait_list_manager.cc b/quic/core/quic_time_wait_list_manager.cc
index fa62fc5..d646f41 100644
--- a/quic/core/quic_time_wait_list_manager.cc
+++ b/quic/core/quic_time_wait_list_manager.cc
@@ -200,7 +200,8 @@
 }
 
 void QuicTimeWaitListManager::SendVersionNegotiationPacket(
-    QuicConnectionId connection_id,
+    QuicConnectionId server_connection_id,
+    QuicConnectionId client_connection_id,
     bool ietf_quic,
     const ParsedQuicVersionVector& supported_versions,
     const QuicSocketAddress& self_address,
@@ -209,7 +210,8 @@
   SendOrQueuePacket(QuicMakeUnique<QueuedPacket>(
                         self_address, peer_address,
                         QuicFramer::BuildVersionNegotiationPacket(
-                            connection_id, ietf_quic, supported_versions)),
+                            server_connection_id, client_connection_id,
+                            ietf_quic, supported_versions)),
                     packet_context.get());
 }
 
diff --git a/quic/core/quic_time_wait_list_manager.h b/quic/core/quic_time_wait_list_manager.h
index dee5d11..26e894d 100644
--- a/quic/core/quic_time_wait_list_manager.h
+++ b/quic/core/quic_time_wait_list_manager.h
@@ -121,7 +121,8 @@
   // Sends a version negotiation packet for |connection_id| announcing support
   // for |supported_versions| to |peer_address| from |self_address|.
   virtual void SendVersionNegotiationPacket(
-      QuicConnectionId connection_id,
+      QuicConnectionId server_connection_id,
+      QuicConnectionId client_connection_id,
       bool ietf_quic,
       const ParsedQuicVersionVector& supported_versions,
       const QuicSocketAddress& self_address,
diff --git a/quic/core/quic_time_wait_list_manager_test.cc b/quic/core/quic_time_wait_list_manager_test.cc
index a391390..c1dadba 100644
--- a/quic/core/quic_time_wait_list_manager_test.cc
+++ b/quic/core/quic_time_wait_list_manager_test.cc
@@ -251,15 +251,16 @@
 
 TEST_F(QuicTimeWaitListManagerTest, SendVersionNegotiationPacket) {
   std::unique_ptr<QuicEncryptedPacket> packet(
-      QuicFramer::BuildVersionNegotiationPacket(connection_id_, false,
+      QuicFramer::BuildVersionNegotiationPacket(connection_id_,
+                                                EmptyQuicConnectionId(), false,
                                                 AllSupportedVersions()));
   EXPECT_CALL(writer_, WritePacket(_, packet->length(), self_address_.host(),
                                    peer_address_, _))
       .WillOnce(Return(WriteResult(WRITE_STATUS_OK, 1)));
 
   time_wait_list_manager_.SendVersionNegotiationPacket(
-      connection_id_, false, AllSupportedVersions(), self_address_,
-      peer_address_, QuicMakeUnique<QuicPerPacketContext>());
+      connection_id_, EmptyQuicConnectionId(), false, AllSupportedVersions(),
+      self_address_, peer_address_, QuicMakeUnique<QuicPerPacketContext>());
   EXPECT_EQ(0u, time_wait_list_manager_.num_connections());
 }
 
diff --git a/quic/core/quic_versions.cc b/quic/core/quic_versions.cc
index a4a241b..45bccc9 100644
--- a/quic/core/quic_versions.cc
+++ b/quic/core/quic_versions.cc
@@ -55,6 +55,16 @@
   return transport_version > QUIC_VERSION_46;
 }
 
+bool ParsedQuicVersion::SupportsClientConnectionIds() const {
+  if (!GetQuicRestartFlag(quic_do_not_override_connection_id)) {
+    // Do not enable this feature in a production version until this flag has
+    // been deprecated.
+    return false;
+  }
+  return transport_version >= QUIC_VERSION_99 ||
+         transport_version == QUIC_VERSION_UNSUPPORTED;
+}
+
 std::ostream& operator<<(std::ostream& os, const ParsedQuicVersion& version) {
   os << ParsedQuicVersionToString(version);
   return os;
diff --git a/quic/core/quic_versions.h b/quic/core/quic_versions.h
index fb811cf..02a0681 100644
--- a/quic/core/quic_versions.h
+++ b/quic/core/quic_versions.h
@@ -162,6 +162,9 @@
 
   // Returns whether this version supports IETF RETRY packets.
   bool SupportsRetry() const;
+
+  // Returns whether this version supports client connection ID.
+  bool SupportsClientConnectionIds() const;
 };
 
 QUIC_EXPORT_PRIVATE ParsedQuicVersion UnsupportedQuicVersion();
diff --git a/quic/test_tools/mock_quic_time_wait_list_manager.h b/quic/test_tools/mock_quic_time_wait_list_manager.h
index d13d5ac..8a39442 100644
--- a/quic/test_tools/mock_quic_time_wait_list_manager.h
+++ b/quic/test_tools/mock_quic_time_wait_list_manager.h
@@ -45,8 +45,9 @@
                     PacketHeaderFormat header_format,
                     std::unique_ptr<QuicPerPacketContext> packet_context));
 
-  MOCK_METHOD6(SendVersionNegotiationPacket,
-               void(QuicConnectionId connection_id,
+  MOCK_METHOD7(SendVersionNegotiationPacket,
+               void(QuicConnectionId server_connection_id,
+                    QuicConnectionId client_connection_id,
                     bool ietf_quic,
                     const ParsedQuicVersionVector& supported_versions,
                     const QuicSocketAddress& server_address,
diff --git a/quic/test_tools/quic_framer_peer.cc b/quic/test_tools/quic_framer_peer.cc
index dcb0e94..6eedd60 100644
--- a/quic/test_tools/quic_framer_peer.cc
+++ b/quic/test_tools/quic_framer_peer.cc
@@ -337,11 +337,11 @@
 }
 
 // static
-void QuicFramerPeer::SetExpectedConnectionIDLength(
+void QuicFramerPeer::SetExpectedServerConnectionIDLength(
     QuicFramer* framer,
-    uint8_t expected_connection_id_length) {
-  *const_cast<uint8_t*>(&framer->expected_connection_id_length_) =
-      expected_connection_id_length;
+    uint8_t expected_server_connection_id_length) {
+  *const_cast<uint8_t*>(&framer->expected_server_connection_id_length_) =
+      expected_server_connection_id_length;
 }
 
 // static
diff --git a/quic/test_tools/quic_framer_peer.h b/quic/test_tools/quic_framer_peer.h
index e363105..0b17c19 100644
--- a/quic/test_tools/quic_framer_peer.h
+++ b/quic/test_tools/quic_framer_peer.h
@@ -160,9 +160,9 @@
                                    QuicPacketNumberLength packet_number_length);
   static void SetFirstSendingPacketNumber(QuicFramer* framer,
                                           uint64_t packet_number);
-  static void SetExpectedConnectionIDLength(
+  static void SetExpectedServerConnectionIDLength(
       QuicFramer* framer,
-      uint8_t expected_connection_id_length);
+      uint8_t expected_server_connection_id_length);
   static QuicPacketNumber GetLargestDecryptedPacketNumber(
       QuicFramer* framer,
       PacketNumberSpace packet_number_space);
diff --git a/quic/test_tools/quic_spdy_session_peer.cc b/quic/test_tools/quic_spdy_session_peer.cc
index 956cd88..6a49bb7 100644
--- a/quic/test_tools/quic_spdy_session_peer.cc
+++ b/quic/test_tools/quic_spdy_session_peer.cc
@@ -81,5 +81,11 @@
   return session->GetNextOutgoingUnidirectionalStreamId();
 }
 
+// static
+QuicReceiveControlStream* QuicSpdySessionPeer::GetReceiveControlStream(
+    QuicSpdySession* session) {
+  return session->receive_control_stream_;
+}
+
 }  // namespace test
 }  // namespace quic
diff --git a/quic/test_tools/quic_spdy_session_peer.h b/quic/test_tools/quic_spdy_session_peer.h
index 47b55e1..414662d 100644
--- a/quic/test_tools/quic_spdy_session_peer.h
+++ b/quic/test_tools/quic_spdy_session_peer.h
@@ -5,6 +5,17 @@
 #ifndef QUICHE_QUIC_TEST_TOOLS_QUIC_SPDY_SESSION_PEER_H_
 #define QUICHE_QUIC_TEST_TOOLS_QUIC_SPDY_SESSION_PEER_H_
 
+<<<<<<<
+|||||||
+#include "net/third_party/quic/core/quic_packets.h"
+#include "net/third_party/quic/core/quic_write_blocked_list.h"
+#include "net/third_party/spdy/core/spdy_framer.h"
+=======
+#include "net/third_party/quic/core/http/quic_receive_control_stream.h"
+#include "net/third_party/quic/core/quic_packets.h"
+#include "net/third_party/quic/core/quic_write_blocked_list.h"
+#include "net/third_party/spdy/core/spdy_framer.h"
+>>>>>>>
 #include "net/third_party/quiche/src/quic/core/quic_packets.h"
 #include "net/third_party/quiche/src/quic/core/quic_write_blocked_list.h"
 #include "net/third_party/quiche/src/spdy/core/spdy_framer.h"
@@ -46,6 +57,8 @@
   // |session| can't be nullptr.
   static QuicStreamId GetNextOutgoingUnidirectionalStreamId(
       QuicSpdySession* session);
+  static QuicReceiveControlStream* GetReceiveControlStream(
+      QuicSpdySession* session);
 };
 
 }  // namespace test
diff --git a/quic/test_tools/quic_test_client.cc b/quic/test_tools/quic_test_client.cc
index 497dd8a..a290e7d 100644
--- a/quic/test_tools/quic_test_client.cc
+++ b/quic/test_tools/quic_test_client.cc
@@ -209,8 +209,10 @@
                                                                this),
           QuicWrapUnique(
               new RecordingProofVerifier(std::move(proof_verifier)))),
-      override_connection_id_(EmptyQuicConnectionId()),
-      connection_id_overridden_(false) {}
+      override_server_connection_id_(EmptyQuicConnectionId()),
+      server_connection_id_overridden_(false),
+      override_client_connection_id_(EmptyQuicConnectionId()),
+      client_connection_id_overridden_(false) {}
 
 MockableQuicClient::~MockableQuicClient() {
   if (connected()) {
@@ -231,13 +233,26 @@
 }
 
 QuicConnectionId MockableQuicClient::GenerateNewConnectionId() {
-  return connection_id_overridden_ ? override_connection_id_
-                                   : QuicClient::GenerateNewConnectionId();
+  return server_connection_id_overridden_
+             ? override_server_connection_id_
+             : QuicClient::GenerateNewConnectionId();
 }
 
-void MockableQuicClient::UseConnectionId(QuicConnectionId connection_id) {
-  connection_id_overridden_ = true;
-  override_connection_id_ = connection_id;
+void MockableQuicClient::UseConnectionId(
+    QuicConnectionId server_connection_id) {
+  server_connection_id_overridden_ = true;
+  override_server_connection_id_ = server_connection_id;
+}
+
+QuicConnectionId MockableQuicClient::GetClientConnectionId() {
+  return client_connection_id_overridden_ ? override_client_connection_id_
+                                          : QuicClient::GetClientConnectionId();
+}
+
+void MockableQuicClient::UseClientConnectionId(
+    QuicConnectionId client_connection_id) {
+  client_connection_id_overridden_ = true;
+  override_client_connection_id_ = client_connection_id;
 }
 
 void MockableQuicClient::UseWriter(QuicPacketWriterWrapper* writer) {
@@ -759,9 +774,15 @@
   client_->UseWriter(writer);
 }
 
-void QuicTestClient::UseConnectionId(QuicConnectionId connection_id) {
+void QuicTestClient::UseConnectionId(QuicConnectionId server_connection_id) {
   DCHECK(!connected());
-  client_->UseConnectionId(connection_id);
+  client_->UseConnectionId(server_connection_id);
+}
+
+void QuicTestClient::UseClientConnectionId(
+    QuicConnectionId client_connection_id) {
+  DCHECK(!connected());
+  client_->UseClientConnectionId(client_connection_id);
 }
 
 bool QuicTestClient::MigrateSocket(const QuicIpAddress& new_host) {
diff --git a/quic/test_tools/quic_test_client.h b/quic/test_tools/quic_test_client.h
index 353c29e..5f1b6fa 100644
--- a/quic/test_tools/quic_test_client.h
+++ b/quic/test_tools/quic_test_client.h
@@ -55,7 +55,9 @@
   ~MockableQuicClient() override;
 
   QuicConnectionId GenerateNewConnectionId() override;
-  void UseConnectionId(QuicConnectionId connection_id);
+  void UseConnectionId(QuicConnectionId server_connection_id);
+  QuicConnectionId GetClientConnectionId() override;
+  void UseClientConnectionId(QuicConnectionId client_connection_id);
 
   void UseWriter(QuicPacketWriterWrapper* writer);
   void set_peer_address(const QuicSocketAddress& address);
@@ -69,9 +71,12 @@
   const MockableQuicClientEpollNetworkHelper* mockable_network_helper() const;
 
  private:
-  // ConnectionId to use, if connection_id_overridden_
-  QuicConnectionId override_connection_id_;
-  bool connection_id_overridden_;
+  // Server connection ID to use, if server_connection_id_overridden_
+  QuicConnectionId override_server_connection_id_;
+  bool server_connection_id_overridden_;
+  // Client connection ID to use, if client_connection_id_overridden_
+  QuicConnectionId override_client_connection_id_;
+  bool client_connection_id_overridden_;
   CachedNetworkParameters cached_network_paramaters_;
 };
 
@@ -219,9 +224,12 @@
   // Configures client_ to take ownership of and use the writer.
   // Must be called before initial connect.
   void UseWriter(QuicPacketWriterWrapper* writer);
-  // If the given ConnectionId is nonzero, configures client_ to use a specific
-  // ConnectionId instead of a random one.
-  void UseConnectionId(QuicConnectionId connection_id);
+  // Configures client_ to use a specific server connection ID instead of a
+  // random one.
+  void UseConnectionId(QuicConnectionId server_connection_id);
+  // Configures client_ to use a specific client connection ID instead of an
+  // empty one.
+  void UseClientConnectionId(QuicConnectionId client_connection_id);
 
   // Returns nullptr if the maximum number of streams have already been created.
   QuicSpdyClientStream* GetOrCreateStream();
diff --git a/quic/test_tools/quic_test_server.cc b/quic/test_tools/quic_test_server.cc
index bda2148..68c500e 100644
--- a/quic/test_tools/quic_test_server.cc
+++ b/quic/test_tools/quic_test_server.cc
@@ -77,7 +77,7 @@
       std::unique_ptr<QuicCryptoServerStream::Helper> session_helper,
       std::unique_ptr<QuicAlarmFactory> alarm_factory,
       QuicSimpleServerBackend* quic_simple_server_backend,
-      uint8_t expected_connection_id_length)
+      uint8_t expected_server_connection_id_length)
       : QuicSimpleDispatcher(config,
                              crypto_config,
                              version_manager,
@@ -85,7 +85,7 @@
                              std::move(session_helper),
                              std::move(alarm_factory),
                              quic_simple_server_backend,
-                             expected_connection_id_length),
+                             expected_server_connection_id_length),
         session_factory_(nullptr),
         stream_factory_(nullptr),
         crypto_stream_factory_(nullptr) {}
@@ -170,13 +170,13 @@
     const QuicConfig& config,
     const ParsedQuicVersionVector& supported_versions,
     QuicSimpleServerBackend* quic_simple_server_backend,
-    uint8_t expected_connection_id_length)
+    uint8_t expected_server_connection_id_length)
     : QuicServer(std::move(proof_source),
                  config,
                  QuicCryptoServerConfig::ConfigOptions(),
                  supported_versions,
                  quic_simple_server_backend,
-                 expected_connection_id_length) {}
+                 expected_server_connection_id_length) {}
 
 QuicDispatcher* QuicTestServer::CreateQuicDispatcher() {
   return new QuicTestDispatcher(
@@ -186,7 +186,7 @@
       std::unique_ptr<QuicCryptoServerStream::Helper>(
           new QuicSimpleCryptoServerStreamHelper(QuicRandom::GetInstance())),
       QuicMakeUnique<QuicEpollAlarmFactory>(epoll_server()), server_backend(),
-      expected_connection_id_length());
+      expected_server_connection_id_length());
 }
 
 void QuicTestServer::SetSessionFactory(SessionFactory* factory) {
diff --git a/quic/test_tools/quic_test_server.h b/quic/test_tools/quic_test_server.h
index 52fb7c5..3661b7a 100644
--- a/quic/test_tools/quic_test_server.h
+++ b/quic/test_tools/quic_test_server.h
@@ -69,7 +69,7 @@
                  const QuicConfig& config,
                  const ParsedQuicVersionVector& supported_versions,
                  QuicSimpleServerBackend* quic_simple_server_backend,
-                 uint8_t expected_connection_id_length);
+                 uint8_t expected_server_connection_id_length);
 
   // Create a custom dispatcher which creates custom sessions.
   QuicDispatcher* CreateQuicDispatcher() override;
diff --git a/quic/test_tools/quic_test_utils.cc b/quic/test_tools/quic_test_utils.cc
index 506d323..6bfdefd 100644
--- a/quic/test_tools/quic_test_utils.cc
+++ b/quic/test_tools/quic_test_utils.cc
@@ -1180,6 +1180,14 @@
          QuicUtils::StreamIdDelta(version) * n;
 }
 
+QuicStreamId GetNthClientInitiatedUnidirectionalStreamId(
+    QuicTransportVersion version,
+    int n) {
+  return QuicUtils::GetFirstUnidirectionalStreamId(version,
+                                                   Perspective::IS_CLIENT) +
+         QuicUtils::StreamIdDelta(version) * n;
+}
+
 StreamType DetermineStreamType(QuicStreamId id,
                                QuicTransportVersion version,
                                Perspective perspective,
diff --git a/quic/test_tools/quic_test_utils.h b/quic/test_tools/quic_test_utils.h
index f64ddbd..3d265fb 100644
--- a/quic/test_tools/quic_test_utils.h
+++ b/quic/test_tools/quic_test_utils.h
@@ -1178,6 +1178,9 @@
 QuicStreamId GetNthServerInitiatedUnidirectionalStreamId(
     QuicTransportVersion version,
     int n);
+QuicStreamId GetNthClientInitiatedUnidirectionalStreamId(
+    QuicTransportVersion version,
+    int n);
 
 StreamType DetermineStreamType(QuicStreamId id,
                                QuicTransportVersion version,
diff --git a/quic/tools/quic_client_base.cc b/quic/tools/quic_client_base.cc
index 57cbd9a..679a0d1 100644
--- a/quic/tools/quic_client_base.cc
+++ b/quic/tools/quic_client_base.cc
@@ -109,6 +109,11 @@
 void QuicClientBase::StartConnect() {
   DCHECK(initialized_);
   DCHECK(!connected());
+  network_helper_->CleanUpAllUDPSockets();
+  if (!network_helper_->CreateUDPSocketAndBind(server_address_,
+                                               bind_to_address_, local_port_)) {
+    return;
+  }
   QuicPacketWriter* writer = network_helper_->CreateQuicPacketWriter();
   ParsedQuicVersion mutual_version = UnsupportedQuicVersion();
   const bool can_reconnect_with_different_version =
@@ -135,6 +140,7 @@
                          can_reconnect_with_different_version
                              ? ParsedQuicVersionVector{mutual_version}
                              : supported_versions()));
+  session()->connection()->set_client_connection_id(GetClientConnectionId());
   if (initial_max_packet_length_ != 0) {
     session()->connection()->SetMaxPacketLength(initial_max_packet_length_);
   }
@@ -333,6 +339,10 @@
   return QuicUtils::CreateRandomConnectionId();
 }
 
+QuicConnectionId QuicClientBase::GetClientConnectionId() {
+  return EmptyQuicConnectionId();
+}
+
 bool QuicClientBase::CanReconnectWithDifferentVersion(
     ParsedQuicVersion* version) const {
   if (session_ == nullptr || session_->connection() == nullptr ||
diff --git a/quic/tools/quic_client_base.h b/quic/tools/quic_client_base.h
index 0cc4d71..134404b 100644
--- a/quic/tools/quic_client_base.h
+++ b/quic/tools/quic_client_base.h
@@ -268,6 +268,9 @@
   // connection ID).
   virtual QuicConnectionId GenerateNewConnectionId();
 
+  // Returns the client connection ID to use.
+  virtual QuicConnectionId GetClientConnectionId();
+
   QuicAlarmFactory* alarm_factory() { return alarm_factory_.get(); }
 
   // Subclasses may need to explicitly clear the session on destruction
diff --git a/quic/tools/quic_server.cc b/quic/tools/quic_server.cc
index 4ac1dac..3696b7c 100644
--- a/quic/tools/quic_server.cc
+++ b/quic/tools/quic_server.cc
@@ -64,7 +64,7 @@
     const QuicCryptoServerConfig::ConfigOptions& crypto_config_options,
     const ParsedQuicVersionVector& supported_versions,
     QuicSimpleServerBackend* quic_simple_server_backend,
-    uint8_t expected_connection_id_length)
+    uint8_t expected_server_connection_id_length)
     : port_(0),
       fd_(-1),
       packets_dropped_(0),
@@ -80,7 +80,8 @@
       version_manager_(supported_versions),
       packet_reader_(new QuicPacketReader()),
       quic_simple_server_backend_(quic_simple_server_backend),
-      expected_connection_id_length_(expected_connection_id_length) {
+      expected_server_connection_id_length_(
+          expected_server_connection_id_length) {
   DCHECK(quic_simple_server_backend_);
   Initialize();
 }
@@ -159,7 +160,7 @@
           new QuicSimpleCryptoServerStreamHelper(QuicRandom::GetInstance())),
       std::unique_ptr<QuicEpollAlarmFactory>(
           new QuicEpollAlarmFactory(&epoll_server_)),
-      quic_simple_server_backend_, expected_connection_id_length_);
+      quic_simple_server_backend_, expected_server_connection_id_length_);
 }
 
 void QuicServer::HandleEventsForever() {
diff --git a/quic/tools/quic_server.h b/quic/tools/quic_server.h
index 6fb1646..1f9c225 100644
--- a/quic/tools/quic_server.h
+++ b/quic/tools/quic_server.h
@@ -43,7 +43,7 @@
              const QuicCryptoServerConfig::ConfigOptions& server_config_options,
              const ParsedQuicVersionVector& supported_versions,
              QuicSimpleServerBackend* quic_simple_server_backend,
-             uint8_t expected_connection_id_length);
+             uint8_t expected_server_connection_id_length);
   QuicServer(const QuicServer&) = delete;
   QuicServer& operator=(const QuicServer&) = delete;
 
@@ -103,8 +103,8 @@
 
   void set_silent_close(bool value) { silent_close_ = value; }
 
-  uint8_t expected_connection_id_length() {
-    return expected_connection_id_length_;
+  uint8_t expected_server_connection_id_length() {
+    return expected_server_connection_id_length_;
   }
 
  private:
@@ -155,7 +155,7 @@
   QuicSimpleServerBackend* quic_simple_server_backend_;  // unowned.
 
   // Connection ID length expected to be read on incoming IETF short headers.
-  uint8_t expected_connection_id_length_;
+  uint8_t expected_server_connection_id_length_;
 };
 
 }  // namespace quic
diff --git a/quic/tools/quic_simple_dispatcher.cc b/quic/tools/quic_simple_dispatcher.cc
index 4706b60..0f4d447 100644
--- a/quic/tools/quic_simple_dispatcher.cc
+++ b/quic/tools/quic_simple_dispatcher.cc
@@ -16,14 +16,14 @@
     std::unique_ptr<QuicCryptoServerStream::Helper> session_helper,
     std::unique_ptr<QuicAlarmFactory> alarm_factory,
     QuicSimpleServerBackend* quic_simple_server_backend,
-    uint8_t expected_connection_id_length)
+    uint8_t expected_server_connection_id_length)
     : QuicDispatcher(config,
                      crypto_config,
                      version_manager,
                      std::move(helper),
                      std::move(session_helper),
                      std::move(alarm_factory),
-                     expected_connection_id_length),
+                     expected_server_connection_id_length),
       quic_simple_server_backend_(quic_simple_server_backend) {}
 
 QuicSimpleDispatcher::~QuicSimpleDispatcher() = default;
diff --git a/quic/tools/quic_simple_dispatcher.h b/quic/tools/quic_simple_dispatcher.h
index 46d976c..8a6cf85 100644
--- a/quic/tools/quic_simple_dispatcher.h
+++ b/quic/tools/quic_simple_dispatcher.h
@@ -21,7 +21,7 @@
       std::unique_ptr<QuicCryptoServerStream::Helper> session_helper,
       std::unique_ptr<QuicAlarmFactory> alarm_factory,
       QuicSimpleServerBackend* quic_simple_server_backend,
-      uint8_t expected_connection_id_length);
+      uint8_t expected_server_connection_id_length);
 
   ~QuicSimpleDispatcher() override;