diff --git a/quic/tools/quic_client_base.cc b/quic/tools/quic_client_base.cc
index 4b51184..11edb19 100644
--- a/quic/tools/quic_client_base.cc
+++ b/quic/tools/quic_client_base.cc
@@ -37,7 +37,9 @@
       connection_error_(QUIC_NO_ERROR),
       connected_or_attempting_connect_(false),
       network_helper_(std::move(network_helper)),
-      connection_debug_visitor_(nullptr) {}
+      connection_debug_visitor_(nullptr),
+      server_connection_id_length_(kQuicDefaultConnectionIdLength),
+      client_connection_id_length_(0) {}
 
 QuicClientBase::~QuicClientBase() = default;
 
@@ -306,11 +308,11 @@
 }
 
 QuicConnectionId QuicClientBase::GenerateNewConnectionId() {
-  return QuicUtils::CreateRandomConnectionId();
+  return QuicUtils::CreateRandomConnectionId(server_connection_id_length_);
 }
 
 QuicConnectionId QuicClientBase::GetClientConnectionId() {
-  return EmptyQuicConnectionId();
+  return QuicUtils::CreateRandomConnectionId(client_connection_id_length_);
 }
 
 bool QuicClientBase::CanReconnectWithDifferentVersion(
diff --git a/quic/tools/quic_client_base.h b/quic/tools/quic_client_base.h
index 6c1e09a..0a40b82 100644
--- a/quic/tools/quic_client_base.h
+++ b/quic/tools/quic_client_base.h
@@ -230,6 +230,14 @@
     connection_debug_visitor_ = connection_debug_visitor;
   }
 
+  void set_server_connection_id_length(uint8_t server_connection_id_length) {
+    server_connection_id_length_ = server_connection_id_length;
+  }
+
+  void set_client_connection_id_length(uint8_t client_connection_id_length) {
+    client_connection_id_length_ = client_connection_id_length;
+  }
+
  protected:
   // TODO(rch): Move GetNumSentClientHellosFromSession and
   // GetNumReceivedServerConfigUpdatesFromSession into a new/better
@@ -352,6 +360,14 @@
   // The debug visitor set on the connection right after it is constructed.
   // Not owned, must be valid for the lifetime of the QuicClientBase instance.
   QuicConnectionDebugVisitor* connection_debug_visitor_;
+
+  // GenerateNewConnectionId creates a random connection ID of this length.
+  // Defaults to 8.
+  uint8_t server_connection_id_length_;
+
+  // GetClientConnectionId creates a random connection ID of this length.
+  // Defaults to 0.
+  uint8_t client_connection_id_length_;
 };
 
 }  // namespace quic
diff --git a/quic/tools/quic_toy_client.cc b/quic/tools/quic_toy_client.cc
index 5733e0b..0018f05 100644
--- a/quic/tools/quic_toy_client.cc
+++ b/quic/tools/quic_toy_client.cc
@@ -165,6 +165,16 @@
     false,
     "If true, do not change local port after each request.");
 
+DEFINE_QUIC_COMMAND_LINE_FLAG(int32_t,
+                              server_connection_id_length,
+                              -1,
+                              "Length of the server connection ID used.");
+
+DEFINE_QUIC_COMMAND_LINE_FLAG(int32_t,
+                              client_connection_id_length,
+                              -1,
+                              "Length of the client connection ID used.");
+
 namespace quic {
 
 QuicToyClient::QuicToyClient(ClientFactory* client_factory)
@@ -235,6 +245,16 @@
   client->set_initial_max_packet_length(
       initial_mtu != 0 ? initial_mtu : quic::kDefaultMaxPacketSize);
   client->set_drop_response_body(GetQuicFlag(FLAGS_drop_response_body));
+  const int32_t server_connection_id_length =
+      GetQuicFlag(FLAGS_server_connection_id_length);
+  if (server_connection_id_length >= 0) {
+    client->set_server_connection_id_length(server_connection_id_length);
+  }
+  const int32_t client_connection_id_length =
+      GetQuicFlag(FLAGS_client_connection_id_length);
+  if (client_connection_id_length >= 0) {
+    client->set_client_connection_id_length(client_connection_id_length);
+  }
   if (!client->Initialize()) {
     std::cerr << "Failed to initialize client." << std::endl;
     return 1;