diff --git a/CMakeLists.txt b/CMakeLists.txt
index 801d331..4d95993 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -2,14 +2,13 @@ cmake_minimum_required(VERSION 3.15.0 FATAL_ERROR)
 
 project(punchnat CXX)
 
-set(CMAKE_C_STANDARD 17)
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 
-if(${CMAKE_SYSTEM_NAME} MATCHES "FreeBSD")
+if(${CMAKE_SYSTEM_NAME} MATCHES "FreeBSD" OR ${CMAKE_SYSTEM_NAME} MATCHES "OpenBSD")
 	include_directories("/usr/local/include")
 	include_directories("/usr/local/include/botan-2")
 endif()
diff --git a/README.md b/README.md
index 3883288..187d8cd 100644
--- a/README.md
+++ b/README.md
@@ -40,6 +40,10 @@ punchnat config1.conf config2.conf
 
 如果不需要写入 Log 文件，那就删除 `log_path` 这一行。
 
+### 参数介绍
+
+
+
 ### STUN Servers
 不支持 TCP 的普通 STUN 服务器（来自于[NatTypeTeste](https://github.com/HMBSbige/NatTypeTester)）
 - stun.syncthing.net
@@ -70,6 +74,8 @@ punchnat config1.conf config2.conf
 - FreeBSD
 - Linux
 
+预编译的二进制文件全部都是静态编译。Linux 版本基本上都是静态编译，但 libc 除外，因此准备了两个版本，一个用于 glibc (2.31)，另一个用于 musl。
+
 ---
 
 ## 建立服务
@@ -157,27 +163,11 @@ make
 ---
 
 ## IPv4 映射 IPv6
-由于该项目内部使用的是 IPv6 单栈 + 开启 IPv4 映射地址（IPv4-mapped IPv6）来使用 IPv4 网络，因此请确保 v6only 选项的值为 0。
+由于 PunchNAT 内部使用的是 IPv6 单栈 + 开启 IPv4 映射地址（IPv4-mapped IPv6）来同时使用 IPv4 与 IPv6 网络，因此请确保 v6only 选项的值为 0。
 
 **正常情况下不需要任何额外设置，FreeBSD 与 Linux 以及 Windows 都默认允许 IPv4 地址映射到 IPv6。**
 
-如果不放心，那么可以这样做
-### FreeBSD
-按照FreeBSD手册 [33.9.5. IPv6 and IPv4 Address Mapping](https://docs.freebsd.org/en/books/handbook/advanced-networking/#_ipv6_and_ipv4_address_mapping) 介绍，在 `/etc/rc.conf` 加一行即可
-```
-ipv6_ipv4mapping="YES"
-```
-如果还是不放心，那就运行命令
-```
-sysctl net.inet6.ip6.v6only=0
-```
-
-### Linux
-可运行命令
-```
-sysctl -w net.ipv6.bindv6only=0
-```
-正常情况下不需要这样做，它的默认值就是 0。
+如果系统不支持 IPv6，或者禁用了 IPv6，请在配置文件中设置 ipv4_only=true，这样 PunchNAT 会退回到使用 IPv4 单栈模式。
 
 ## 其它注意事项
 ### NetBSD
@@ -187,13 +177,13 @@ sysctl -w net.inet6.ip6.v6only=0
 ```
 设置后，单栈+映射地址模式可以侦听双栈。
 
-但由于未知的原因，它无法主动连接 IPv4 映射地址，因此 `destination_address` 只能使用 IPv6 地址。
+但由于未知的原因，可能无法主动连接 IPv4 映射地址。
 
 ### OpenBSD
-因为 OpenBSD 彻底屏蔽了 IPv4 映射地址，所以在 OpenBSD 平台只能使用 IPv6 单栈模式。
+因为 OpenBSD 彻底屏蔽了 IPv4 映射地址，所以在 OpenBSD 平台使用双栈的话，需要将配置文件保存成两个，其中一个启用 ipv4_only=1，然后在使用 PunchNAT 时同时载入两个配置文件。
 
 ## 关于代码
-### 为什么要用两个 asio::io_context
-这里用了两个 asio::io_context，其中一个是用于处理 UDP 数据的异步循环，另一个用于处理内部逻辑以及 TCP 数据的收发。
+### 版面
+代码写得很随意，想到哪写到哪，因此版面混乱。
 
-之所以要这样做，完全是为了迁就 BSD 系统。如果只用一个 io_context 去做所有的事，由于两次接收之间的延迟过高，在 BSD 平台会导致 UDP 丢包率过高。
\ No newline at end of file
+至于阅读者的感受嘛…… 那肯定会不爽。
\ No newline at end of file
diff --git a/src/main.cpp b/src/main.cpp
index 825fee7..e0f9e04 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -14,7 +14,7 @@ int main(int argc, char *argv[])
 	if (argc <= 1)
 	{
 		char app_name[] = "punchnat";
-		printf("%s version 20230415\n", app_name);
+		printf("%s version 20230423\n", app_name);
 		printf("Usage: %s config1.conf\n", app_name);
 		printf("       %s config1.conf config2.conf...\n", app_name);
 		return 0;
diff --git a/src/networks/connections.cpp b/src/networks/connections.cpp
index 2e70993..1435aee 100644
--- a/src/networks/connections.cpp
+++ b/src/networks/connections.cpp
@@ -27,12 +27,16 @@ void empty_tcp_disconnect(tcp_session *tmp)
 {
 }
 
-std::unique_ptr<rfc3489::stun_header> send_stun_3489_request(udp_server &sender, const std::string &stun_host)
+std::unique_ptr<rfc3489::stun_header> send_stun_3489_request(udp_server &sender, const std::string &stun_host, bool v4_only)
 {
+	auto udp_version = v4_only ? udp::v4() : udp::v6();
+	udp::resolver::resolver_base::flags input_flags = udp::resolver::numeric_service | udp::resolver::v4_mapped | udp::resolver::all_matching;
+	if (v4_only)
+		input_flags = udp::resolver::numeric_service;
+
 	asio::error_code ec;
 	udp::resolver &udp_resolver = sender.get_resolver();
-	udp::resolver::results_type remote_addresses = udp_resolver.resolve(udp::v6(), stun_host, "3478",
-		udp::resolver::numeric_service | udp::resolver::v4_mapped | udp::resolver::all_matching, ec);
+	udp::resolver::results_type remote_addresses = udp_resolver.resolve(udp_version, stun_host, "3478", input_flags, ec);
 
 	if (ec)
 		return nullptr;
@@ -50,12 +54,16 @@ std::unique_ptr<rfc3489::stun_header> send_stun_3489_request(udp_server &sender,
 	return header;
 }
 
-std::unique_ptr<rfc8489::stun_header> send_stun_8489_request(udp_server &sender, const std::string &stun_host)
+std::unique_ptr<rfc8489::stun_header> send_stun_8489_request(udp_server &sender, const std::string &stun_host, bool v4_only)
 {
+	auto udp_version = v4_only ? udp::v4() : udp::v6();
+	udp::resolver::resolver_base::flags input_flags = udp::resolver::numeric_service | udp::resolver::v4_mapped | udp::resolver::all_matching;
+	if (v4_only)
+		input_flags = udp::resolver::numeric_service;
+
 	asio::error_code ec;
 	udp::resolver &udp_resolver = sender.get_resolver();
-	udp::resolver::results_type remote_addresses = udp_resolver.resolve(udp::v6(), stun_host, "3478",
-		udp::resolver::numeric_service | udp::resolver::v4_mapped | udp::resolver::all_matching, ec);
+	udp::resolver::results_type remote_addresses = udp_resolver.resolve(udp_version, stun_host, "3478", input_flags, ec);
 
 	if (ec)
 		return nullptr;
@@ -74,12 +82,16 @@ std::unique_ptr<rfc8489::stun_header> send_stun_8489_request(udp_server &sender,
 	return header;
 }
 
-void resend_stun_8489_request(udp_server &sender, const std::string &stun_host, rfc8489::stun_header *header)
+void resend_stun_8489_request(udp_server &sender, const std::string &stun_host, rfc8489::stun_header *header, bool v4_only)
 {
+	auto udp_version = v4_only ? udp::v4() : udp::v6();
+	udp::resolver::resolver_base::flags input_flags = udp::resolver::numeric_service | udp::resolver::v4_mapped | udp::resolver::all_matching;
+	if (v4_only)
+		input_flags = udp::resolver::numeric_service;
+
 	asio::error_code ec;
 	udp::resolver &udp_resolver = sender.get_resolver();
-	udp::resolver::results_type remote_addresses = udp_resolver.resolve(udp::v6(), stun_host, "3478",
-		udp::resolver::numeric_service | udp::resolver::v4_mapped | udp::resolver::all_matching, ec);
+	udp::resolver::results_type remote_addresses = udp_resolver.resolve(udp_version, stun_host, "3478", input_flags, ec);
 
 	if (ec)
 		return;
@@ -265,7 +277,8 @@ void tcp_server::acceptor_initialise(tcp::endpoint ep)
 {
 	asio::ip::v6_only v6_option(false);
 	tcp_acceptor.open(ep.protocol());
-	tcp_acceptor.set_option(v6_option);
+	if (ep.address().is_v6())
+		tcp_acceptor.set_option(v6_option);
 	tcp_acceptor.set_option(tcp::no_delay(true));
 	tcp_acceptor.bind(ep);
 	tcp_acceptor.listen(tcp_acceptor.max_connections);
@@ -320,8 +333,12 @@ bool tcp_client::set_remote_hostname(const std::string &remote_address, asio::ip
 
 bool tcp_client::set_remote_hostname(const std::string &remote_address, const std::string &port_num, asio::error_code &ec)
 {
-	remote_endpoints = resolver.resolve(tcp::v6(), remote_address, port_num,
-		tcp::resolver::numeric_service | tcp::resolver::v4_mapped | tcp::resolver::all_matching, ec);
+	auto tcp_version = ipv4_only ? tcp::v4() : tcp::v6();
+	tcp::resolver::resolver_base::flags input_flags = tcp::resolver::numeric_service | tcp::resolver::v4_mapped | tcp::resolver::all_matching;
+	if (ipv4_only)
+		input_flags = tcp::resolver::numeric_service;
+	
+	remote_endpoints = resolver.resolve(tcp_version, remote_address, port_num, input_flags, ec);
 
 	return remote_endpoints.size() > 0;
 }
@@ -356,7 +373,8 @@ void udp_server::initialise(udp::endpoint ep)
 {
 	asio::ip::v6_only v6_option(false);
 	connection_socket.open(ep.protocol());
-	connection_socket.set_option(v6_option);
+	if (ep.address().is_v6())
+		connection_socket.set_option(v6_option);
 	connection_socket.bind(ep);
 }
 
@@ -427,10 +445,12 @@ udp::resolver::results_type udp_client::get_remote_hostname(const std::string &r
 
 udp::resolver::results_type udp_client::get_remote_hostname(const std::string &remote_address, const std::string &port_num, asio::error_code &ec)
 {
-	udp::resolver::results_type remote_addresses = resolver.resolve(udp::v6(), remote_address, port_num,
-		udp::resolver::numeric_service | udp::resolver::v4_mapped | udp::resolver::all_matching, ec);
-
-	return remote_addresses;
+	if (ipv4_only)
+		return resolver.resolve(udp::v4(), remote_address, port_num,
+			udp::resolver::numeric_service | udp::resolver::address_configured, ec);
+	else
+		return resolver.resolve(udp::v6(), remote_address, port_num,
+			udp::resolver::numeric_service | udp::resolver::v4_mapped | udp::resolver::all_matching, ec);
 }
 
 void udp_client::disconnect()
@@ -523,7 +543,8 @@ void udp_client::initialise()
 {
 	asio::ip::v6_only v6_option(false);
 	connection_socket.open(udp::v6());
-	connection_socket.set_option(v6_option);
+	if (!ipv4_only)
+		connection_socket.set_option(v6_option);
 }
 
 void udp_client::start_receive()
diff --git a/src/networks/connections.hpp b/src/networks/connections.hpp
index c946ac6..bd2626d 100644
--- a/src/networks/connections.hpp
+++ b/src/networks/connections.hpp
@@ -122,8 +122,8 @@ class tcp_client
 {
 public:
 	tcp_client() = delete;
-	tcp_client(asio::io_context &io_context)
-		: internal_io_context(io_context), resolver(io_context)
+	tcp_client(asio::io_context &io_context, bool v4_only = false)
+		: internal_io_context(io_context), resolver(io_context), ipv4_only(v4_only)
 	{
 	}
 
@@ -137,6 +137,7 @@ class tcp_client
 	asio::io_context &internal_io_context;
 	tcp::resolver resolver;
 	asio::ip::basic_resolver_results<asio::ip::tcp> remote_endpoints;
+	const bool ipv4_only;
 };
 
 
@@ -177,10 +178,10 @@ class udp_client
 {
 public:
 	udp_client() = delete;
-	udp_client(asio::io_context &io_context, asio::strand<asio::io_context::executor_type> &asio_strand, udp_callback_t callback_func)
+	udp_client(asio::io_context &io_context, asio::strand<asio::io_context::executor_type> &asio_strand, udp_callback_t callback_func, bool v4_only = false)
 		: connection_socket(io_context), resolver(io_context), callback(callback_func), task_assigner(asio_strand),
 		last_receive_time(right_now()), last_send_time(right_now()),
-		paused(false), stopped(false)
+		paused(false), stopped(false), ipv4_only(v4_only)
 	{
 		initialise();
 	}
@@ -225,12 +226,13 @@ class udp_client
 	std::atomic<int64_t> last_send_time;
 	std::atomic<bool> paused;
 	std::atomic<bool> stopped;
+	const bool ipv4_only;
 };
 
 
-std::unique_ptr<rfc3489::stun_header> send_stun_3489_request(udp_server &sender, const std::string &stun_host);
-std::unique_ptr<rfc8489::stun_header> send_stun_8489_request(udp_server &sender, const std::string &stun_host);
-void resend_stun_8489_request(udp_server &sender, const std::string &stun_host, rfc8489::stun_header *header);
+std::unique_ptr<rfc3489::stun_header> send_stun_3489_request(udp_server &sender, const std::string &stun_host, bool v4_only = false);
+std::unique_ptr<rfc8489::stun_header> send_stun_8489_request(udp_server &sender, const std::string &stun_host, bool v4_only = false);
+void resend_stun_8489_request(udp_server &sender, const std::string &stun_host, rfc8489::stun_header *header, bool v4_only = false);
 std::unique_ptr<rfc8489::stun_header> send_stun_8489_request(tcp_session &sender, const std::string &stun_host);
 void resend_stun_8489_request(tcp_session &sender, const std::string &stun_host, rfc8489::stun_header *header);
 
diff --git a/src/networks/tcp_mode.cpp b/src/networks/tcp_mode.cpp
index 3441d92..c8b021c 100644
--- a/src/networks/tcp_mode.cpp
+++ b/src/networks/tcp_mode.cpp
@@ -26,7 +26,12 @@ bool tcp_mode::start()
 	if (port_number == 0)
 		return false;
 
-	tcp::endpoint listen_on_ep(tcp::v6(), port_number);
+	tcp::endpoint listen_on_ep;
+	if (current_settings.ipv4_only)
+		listen_on_ep = tcp::endpoint(tcp::v4(), port_number);
+	else
+		listen_on_ep = tcp::endpoint(tcp::v6(), port_number);
+
 	if (!current_settings.listen_on.empty())
 	{
 		asio::error_code ec;
@@ -39,7 +44,7 @@ bool tcp_mode::start()
 			return false;
 		}
 
-		if (local_address.is_v4())
+		if (local_address.is_v4() && !current_settings.ipv4_only)
 			listen_on_ep.address(asio::ip::make_address_v6(asio::ip::v4_mapped, local_address.to_v4()));
 		else
 			listen_on_ep.address(local_address);
@@ -70,7 +75,7 @@ void tcp_mode::tcp_server_accept_incoming(std::unique_ptr<tcp_session> &&incomin
 	if (!incoming_session->is_open())
 		return;
 
-	tcp_client target_connector(io_context);
+	tcp_client target_connector(io_context, current_settings.ipv4_only);
 	std::string &destination_address = current_settings.destination_address;
 	uint16_t destination_port = current_settings.destination_port;
 	asio::error_code ec;
diff --git a/src/networks/udp_mode.cpp b/src/networks/udp_mode.cpp
index d36763e..5da73c6 100644
--- a/src/networks/udp_mode.cpp
+++ b/src/networks/udp_mode.cpp
@@ -23,7 +23,12 @@ bool udp_mode::start()
 	if (port_number == 0)
 		return false;
 
-	udp::endpoint listen_on_ep(udp::v6(), port_number);
+	udp::endpoint listen_on_ep;
+	if (current_settings.ipv4_only)
+		listen_on_ep = udp::endpoint(udp::v4(), port_number);
+	else
+		listen_on_ep = udp::endpoint(udp::v6(), port_number);
+
 	if (!current_settings.listen_on.empty())
 	{
 		asio::error_code ec;
@@ -36,7 +41,7 @@ bool udp_mode::start()
 			return false;
 		}
 
-		if (local_address.is_v4())
+		if (local_address.is_v4() && !current_settings.ipv4_only)
 			listen_on_ep.address(asio::ip::make_address_v6(asio::ip::v4_mapped, local_address.to_v4()));
 		else
 			listen_on_ep.address(local_address);
@@ -53,7 +58,7 @@ bool udp_mode::start()
 		
 		if (!current_settings.stun_server.empty())
 		{
-			stun_header = send_stun_8489_request(*udp_access_point, current_settings.stun_server);
+			stun_header = send_stun_8489_request(*udp_access_point, current_settings.stun_server, current_settings.ipv4_only);
 			timer_stun.expires_after(std::chrono::seconds(1));
 			timer_stun.async_wait([this](const asio::error_code &e) { send_stun_request(e); });
 		}
@@ -106,7 +111,7 @@ void udp_mode::udp_server_incoming(std::unique_ptr<uint8_t[]> data, size_t data_
 					return;
 
 				auto udp_func = std::bind(&udp_mode::udp_client_incoming_to_udp, this, _1, _2, _3, _4);
-				auto udp_forwarder = std::make_unique<udp_client>(network_io, asio_strand, udp_func);
+				auto udp_forwarder = std::make_unique<udp_client>(network_io, asio_strand, udp_func, current_settings.ipv4_only);
 				if (udp_forwarder == nullptr)
 					return;
 
@@ -232,7 +237,7 @@ void udp_mode::send_stun_request(const asio::error_code &e)
 		return;
 
 	if (!current_settings.stun_server.empty())
-		resend_stun_8489_request(*udp_access_point, current_settings.stun_server, stun_header.get());
+		resend_stun_8489_request(*udp_access_point, current_settings.stun_server, stun_header.get(), current_settings.ipv4_only);
 
 	timer_stun.expires_after(STUN_RESEND);
 	timer_stun.async_wait([this](const asio::error_code &e) { send_stun_request(e); });
diff --git a/src/shares/share_defines.cpp b/src/shares/share_defines.cpp
index 5a562aa..0b567d1 100644
--- a/src/shares/share_defines.cpp
+++ b/src/shares/share_defines.cpp
@@ -76,6 +76,13 @@ user_settings parse_from_args(const std::vector<std::string> &args, std::vector<
 				current_user_settings.udp_timeout = static_cast<uint16_t>(time_interval);
 			break;
 
+		case strhash("ipv4_only"):
+		{
+			bool yes = value == "yes" || value == "true" || value == "1";
+			current_user_settings.ipv4_only = yes;
+			break;
+		}
+		
 		default:
 			error_msg.emplace_back("unknow option: " + arg);
 		}
@@ -145,7 +152,8 @@ void print_ip_to_file(const std::string& message, const std::filesystem::path& l
 	static std::mutex mtx;
 	std::unique_lock locker{ mtx };
 	output_file.open(log_file, std::ios::out | std::ios::trunc);
-	output_file << message;
+	if (output_file.is_open() && output_file.good())
+		output_file << message;
 	output_file.close();
 }
 
@@ -155,6 +163,7 @@ void print_message_to_file(const std::string& message, const std::filesystem::pa
 	static std::mutex mtx;
 	std::unique_lock locker{ mtx };
 	output_file.open(log_file, std::ios::out | std::ios::app);
-	output_file << message;
+	if (output_file.is_open() && output_file.good())
+		output_file << message;
 	output_file.close();
 }
diff --git a/src/shares/share_defines.hpp b/src/shares/share_defines.hpp
index e0ffeac..f06b5ec 100644
--- a/src/shares/share_defines.hpp
+++ b/src/shares/share_defines.hpp
@@ -14,9 +14,9 @@
 template<typename T>
 T generate_random_number()
 {
-	std::random_device rd;
-	std::mt19937 mt(rd());
-	std::uniform_int_distribution<T> uniform_dist(std::numeric_limits<T>::min(), std::numeric_limits<T>::max());
+	thread_local std::random_device rd;
+	thread_local std::mt19937 mt(rd());
+	thread_local std::uniform_int_distribution<T> uniform_dist(std::numeric_limits<T>::min(), std::numeric_limits<T>::max());
 	return uniform_dist(mt);
 }
 
@@ -25,6 +25,7 @@ struct user_settings
 	uint16_t listen_port = 0;
 	uint16_t destination_port = 0;
 	uint16_t udp_timeout = 0;
+	bool ipv4_only = false;
 	std::string listen_on;
 	std::string destination_address;
 	std::string stun_server;