diff --git a/include/libtorrent/aux_/session_impl.hpp b/include/libtorrent/aux_/session_impl.hpp
index 00cb2192f..bff217231 100644
--- a/include/libtorrent/aux_/session_impl.hpp
+++ b/include/libtorrent/aux_/session_impl.hpp
@@ -1089,14 +1089,14 @@ namespace aux {
 				, int port
 				, span<char const> p
 				, error_code& ec
-				, int flags);
+				, udp_send_flags_t flags);
 
 			void send_udp_packet_hostname_listen(aux::listen_socket_handle const& sock
 				, char const* hostname
 				, int port
 				, span<char const> p
 				, error_code& ec
-				, int flags)
+				, udp_send_flags_t const flags)
 			{
 				listen_socket_t* s = sock.get();
 				if (!s)
@@ -1111,13 +1111,13 @@ namespace aux {
 				, udp::endpoint const& ep
 				, span<char const> p
 				, error_code& ec
-				, int flags);
+				, udp_send_flags_t flags);
 
 			void send_udp_packet_listen(aux::listen_socket_handle const& sock
 				, udp::endpoint const& ep
 				, span<char const> p
 				, error_code& ec
-				, int flags)
+				, udp_send_flags_t const flags)
 			{
 				listen_socket_t* s = sock.get();
 				if (!s)
diff --git a/include/libtorrent/kademlia/dht_tracker.hpp b/include/libtorrent/kademlia/dht_tracker.hpp
index 03a5a2d7e..44cb15021 100644
--- a/include/libtorrent/kademlia/dht_tracker.hpp
+++ b/include/libtorrent/kademlia/dht_tracker.hpp
@@ -44,6 +44,7 @@ POSSIBILITY OF SUCH DAMAGE.
 #include <libtorrent/deadline_timer.hpp>
 #include <libtorrent/span.hpp>
 #include <libtorrent/io_service.hpp>
+#include <libtorrent/udp_socket.hpp>
 
 namespace libtorrent {
 
@@ -62,7 +63,7 @@ namespace libtorrent { namespace dht {
 	{
 		using send_fun_t = std::function<void(
 			aux::listen_socket_handle const&, udp::endpoint const&
-			, span<char const>, error_code&, int)>;
+			, span<char const>, error_code&, udp_send_flags_t)>;
 
 		dht_tracker(dht_observer* observer
 			, io_service& ios
diff --git a/include/libtorrent/tracker_manager.hpp b/include/libtorrent/tracker_manager.hpp
index 39d562154..9791da2c1 100644
--- a/include/libtorrent/tracker_manager.hpp
+++ b/include/libtorrent/tracker_manager.hpp
@@ -63,6 +63,7 @@ POSSIBILITY OF SUCH DAMAGE.
 #include "libtorrent/debug.hpp"
 #include "libtorrent/error_code.hpp"
 #include "libtorrent/aux_/listen_socket_handle.hpp"
+#include "libtorrent/udp_socket.hpp"
 
 namespace libtorrent {
 
@@ -341,11 +342,11 @@ namespace libtorrent {
 		typedef std::function<void(aux::listen_socket_handle const&
 			, udp::endpoint const&
 			, span<char const>
-			, error_code&, int)> send_fun_t;
+			, error_code&, udp_send_flags_t)> send_fun_t;
 		typedef std::function<void(aux::listen_socket_handle const&
 			, char const*, int
 			, span<char const>
-			, error_code&, int)> send_fun_hostname_t;
+			, error_code&, udp_send_flags_t)> send_fun_hostname_t;
 
 		tracker_manager(send_fun_t const& send_fun
 			, send_fun_hostname_t const& send_fun_hostname
@@ -391,11 +392,11 @@ namespace libtorrent {
 
 		void send_hostname(aux::listen_socket_handle const& sock
 			, char const* hostname, int port, span<char const> p
-			, error_code& ec, int flags = 0);
+			, error_code& ec, udp_send_flags_t flags = {});
 
 		void send(aux::listen_socket_handle const& sock
 			, udp::endpoint const& ep, span<char const> p
-			, error_code& ec, int flags = 0);
+			, error_code& ec, udp_send_flags_t flags = {});
 
 	private:
 
diff --git a/include/libtorrent/udp_socket.hpp b/include/libtorrent/udp_socket.hpp
index 3c7deadc8..4293dbf0f 100644
--- a/include/libtorrent/udp_socket.hpp
+++ b/include/libtorrent/udp_socket.hpp
@@ -39,6 +39,7 @@ POSSIBILITY OF SUCH DAMAGE.
 #include "libtorrent/aux_/proxy_settings.hpp"
 #include "libtorrent/debug.hpp"
 #include "libtorrent/span.hpp"
+#include "libtorrent/flags.hpp"
 
 #include <array>
 #include <memory>
@@ -47,17 +48,18 @@ namespace libtorrent {
 
 	struct socks5;
 
+	struct udp_send_flags_tag;
+	using udp_send_flags_t = flags::bitfield_flag<std::uint8_t, udp_send_flags_tag>;
+
 	class TORRENT_EXTRA_EXPORT udp_socket : single_threaded
 	{
 	public:
 		explicit udp_socket(io_service& ios);
 
-		enum flags_t {
-			peer_connection = 1
-			, tracker_connection = 2
-			, dont_queue = 4
-			, dont_fragment = 8
-		};
+		static constexpr udp_send_flags_t peer_connection{1};
+		static constexpr udp_send_flags_t tracker_connection{2};
+		static constexpr udp_send_flags_t dont_queue{4};
+		static constexpr udp_send_flags_t dont_fragment{8};
 
 		bool is_open() const { return m_abort == false; }
 		io_service& get_io_service() { return m_socket.get_io_service(); }
@@ -85,10 +87,10 @@ namespace libtorrent {
 
 		// this is only valid when using a socks5 proxy
 		void send_hostname(char const* hostname, int port, span<char const> p
-			, error_code& ec, int flags = 0);
+			, error_code& ec, udp_send_flags_t flags = {});
 
 		void send(udp::endpoint const& ep, span<char const> p
-			, error_code& ec, int flags = 0);
+			, error_code& ec, udp_send_flags_t flags = {});
 		void open(udp const& protocol, error_code& ec);
 		void bind(udp::endpoint const& ep, error_code& ec);
 		void close();
@@ -136,8 +138,8 @@ namespace libtorrent {
 		udp_socket(udp_socket const&);
 		udp_socket& operator=(udp_socket const&);
 
-		void wrap(udp::endpoint const& ep, span<char const> p, error_code& ec, int flags);
-		void wrap(char const* hostname, int port, span<char const> p, error_code& ec, int flags);
+		void wrap(udp::endpoint const& ep, span<char const> p, error_code& ec, udp_send_flags_t flags);
+		void wrap(char const* hostname, int port, span<char const> p, error_code& ec, udp_send_flags_t flags);
 		bool unwrap(udp::endpoint& from, span<char>& buf);
 
 		udp::socket m_socket;
diff --git a/include/libtorrent/utp_socket_manager.hpp b/include/libtorrent/utp_socket_manager.hpp
index 5296e09b7..af837c3a4 100644
--- a/include/libtorrent/utp_socket_manager.hpp
+++ b/include/libtorrent/utp_socket_manager.hpp
@@ -59,20 +59,18 @@ namespace libtorrent {
 
 	struct utp_socket_manager
 	{
-		typedef std::function<void(std::weak_ptr<utp_socket_interface>
+		using send_fun_t = std::function<void(std::weak_ptr<utp_socket_interface>
 			, udp::endpoint const&
 			, span<char const>
-			, error_code&, int)> send_fun_t;
+			, error_code&, udp_send_flags_t)>;
 
-		typedef std::function<void(std::shared_ptr<socket_type> const&)>
-			incoming_utp_callback_t;
+		using incoming_utp_callback_t =  std::function<void(std::shared_ptr<socket_type> const&)>;
 
 		utp_socket_manager(send_fun_t const& send_fun
 			, incoming_utp_callback_t const& cb
 			, io_service& ios
 			, aux::session_settings const& sett
-			, counters& cnt, void* ssl_context
-			);
+			, counters& cnt, void* ssl_context);
 		~utp_socket_manager();
 
 		// return false if this is not a uTP packet
@@ -90,11 +88,9 @@ namespace libtorrent {
 
 		void tick(time_point now);
 
-		// flags for send_packet
-		enum { dont_fragment = 1 };
 		void send_packet(std::weak_ptr<utp_socket_interface> sock, udp::endpoint const& ep
 			, char const* p, int len
-			, error_code& ec, int flags = 0);
+			, error_code& ec, udp_send_flags_t flags = {});
 		void subscribe_writable(utp_socket_impl* s);
 
 		void remove_udp_socket(std::weak_ptr<utp_socket_interface> sock);
diff --git a/simulation/test_dht_rate_limit.cpp b/simulation/test_dht_rate_limit.cpp
index 8fc51356e..599ebce8e 100644
--- a/simulation/test_dht_rate_limit.cpp
+++ b/simulation/test_dht_rate_limit.cpp
@@ -86,7 +86,7 @@ struct obs : dht::dht_observer
 };
 
 void send_packet(lt::udp_socket& sock, lt::aux::listen_socket_handle const&, udp::endpoint const& ep
-	, span<char const> p, error_code& ec, int flags)
+	, span<char const> p, error_code& ec, udp_send_flags_t const flags)
 {
 	sock.send(ep, p, ec, flags);
 }
diff --git a/src/kademlia/dht_tracker.cpp b/src/kademlia/dht_tracker.cpp
index e0eb36cc9..568906e75 100644
--- a/src/kademlia/dht_tracker.cpp
+++ b/src/kademlia/dht_tracker.cpp
@@ -679,13 +679,13 @@ namespace libtorrent { namespace dht {
 					{ return v.first.get_local_endpoint().protocol().family() == addr.protocol().family(); });
 
 			if (n != m_nodes.end())
-				m_send_fun(n->first, addr, m_send_buf, ec, 0);
+				m_send_fun(n->first, addr, m_send_buf, ec, {});
 			else
 				ec = boost::asio::error::address_family_not_supported;
 		}
 		else
 		{
-			m_send_fun(s, addr, m_send_buf, ec, 0);
+			m_send_fun(s, addr, m_send_buf, ec, {});
 		}
 
 		if (ec)
diff --git a/src/session_impl.cpp b/src/session_impl.cpp
index edb317377..9a3a4c3b6 100644
--- a/src/session_impl.cpp
+++ b/src/session_impl.cpp
@@ -2326,7 +2326,7 @@ namespace {
 		, int const port
 		, span<char const> p
 		, error_code& ec
-		, int const flags)
+		, udp_send_flags_t const flags)
 	{
 		auto si = sock.lock();
 		if (!si)
@@ -2353,7 +2353,7 @@ namespace {
 		, udp::endpoint const& ep
 		, span<char const> p
 		, error_code& ec
-		, int const flags)
+		, udp_send_flags_t const flags)
 	{
 		auto si = sock.lock();
 		if (!si)
@@ -5677,7 +5677,7 @@ namespace {
 				, udp::endpoint const& ep
 				, span<char const> p
 				, error_code& ec
-				, int flags)
+				, udp_send_flags_t const flags)
 				{ send_udp_packet_listen(sock, ep, p, ec, flags); }
 			, m_dht_settings
 			, m_stats_counters
diff --git a/src/tracker_manager.cpp b/src/tracker_manager.cpp
index 99e95a36f..05c04baec 100644
--- a/src/tracker_manager.cpp
+++ b/src/tracker_manager.cpp
@@ -377,7 +377,7 @@ namespace libtorrent {
 
 	void tracker_manager::send_hostname(aux::listen_socket_handle const& sock
 		, char const* hostname, int const port
-		, span<char const> p, error_code& ec, int const flags)
+		, span<char const> p, error_code& ec, udp_send_flags_t const flags)
 	{
 		TORRENT_ASSERT(is_single_thread());
 		m_send_fun_hostname(sock, hostname, port, p, ec, flags);
@@ -386,7 +386,7 @@ namespace libtorrent {
 	void tracker_manager::send(aux::listen_socket_handle const& sock
 		, udp::endpoint const& ep
 		, span<char const> p
-		, error_code& ec, int const flags)
+		, error_code& ec, udp_send_flags_t const flags)
 	{
 		TORRENT_ASSERT(is_single_thread());
 		m_send_fun(sock, ep, p, ec, flags);
diff --git a/src/udp_socket.cpp b/src/udp_socket.cpp
index 2b26e2fd7..a6607033a 100644
--- a/src/udp_socket.cpp
+++ b/src/udp_socket.cpp
@@ -223,7 +223,7 @@ int udp_socket::read(span<packet> pkts, error_code& ec)
 }
 
 void udp_socket::send_hostname(char const* hostname, int const port
-	, span<char const> p, error_code& ec, int const flags)
+	, span<char const> p, error_code& ec, udp_send_flags_t const flags)
 {
 	TORRENT_ASSERT(is_single_thread());
 
@@ -254,7 +254,7 @@ void udp_socket::send_hostname(char const* hostname, int const port
 }
 
 void udp_socket::send(udp::endpoint const& ep, span<char const> p
-	, error_code& ec, int const flags)
+	, error_code& ec, udp_send_flags_t const flags)
 {
 	TORRENT_ASSERT(is_single_thread());
 
@@ -268,7 +268,7 @@ void udp_socket::send(udp::endpoint const& ep, span<char const> p
 	const bool allow_proxy
 		= ((flags & peer_connection) && m_proxy_settings.proxy_peer_connections)
 		|| ((flags & tracker_connection) && m_proxy_settings.proxy_tracker_connections)
-		|| (flags & (tracker_connection | peer_connection)) == 0
+		|| !(flags & (tracker_connection | peer_connection))
 		;
 
 	if (allow_proxy && m_socks5_connection && m_socks5_connection->active())
@@ -281,14 +281,14 @@ void udp_socket::send(udp::endpoint const& ep, span<char const> p
 	if (m_force_proxy) return;
 
 	// set the DF flag for the socket and clear it again in the destructor
-	set_dont_frag df(m_socket, (flags & dont_fragment) != 0
+	set_dont_frag df(m_socket, (flags & dont_fragment)
 		&& ep.protocol() == udp::v4());
 
 	m_socket.send_to(boost::asio::buffer(p.data(), p.size()), ep, 0, ec);
 }
 
 void udp_socket::wrap(udp::endpoint const& ep, span<char const> p
-	, error_code& ec, int const flags)
+	, error_code& ec, udp_send_flags_t const flags)
 {
 	TORRENT_UNUSED(flags);
 	using namespace libtorrent::detail;
@@ -306,14 +306,14 @@ void udp_socket::wrap(udp::endpoint const& ep, span<char const> p
 	iovec[1] = boost::asio::const_buffer(p.data(), p.size());
 
 	// set the DF flag for the socket and clear it again in the destructor
-	set_dont_frag df(m_socket, (flags & dont_fragment) != 0
+	set_dont_frag df(m_socket, (flags & dont_fragment)
 		&& ep.protocol() == udp::v4());
 
 	m_socket.send_to(iovec, m_socks5_connection->target(), 0, ec);
 }
 
 void udp_socket::wrap(char const* hostname, int const port, span<char const> p
-	, error_code& ec, int const flags)
+	, error_code& ec, udp_send_flags_t const flags)
 {
 	TORRENT_UNUSED(flags);
 	using namespace libtorrent::detail;
@@ -335,7 +335,7 @@ void udp_socket::wrap(char const* hostname, int const port, span<char const> p
 	iovec[1] = boost::asio::const_buffer(p.data(), p.size());
 
 	// set the DF flag for the socket and clear it again in the destructor
-	set_dont_frag df(m_socket, (flags & dont_fragment) != 0
+	set_dont_frag df(m_socket, (flags & dont_fragment)
 		&& m_socket.local_endpoint(ec).protocol() == udp::v4());
 
 	m_socket.send_to(iovec, m_socks5_connection->target(), 0, ec);
@@ -762,4 +762,9 @@ void socks5::close()
 	m_timer.cancel();
 }
 
+constexpr udp_send_flags_t udp_socket::peer_connection;
+constexpr udp_send_flags_t udp_socket::tracker_connection;
+constexpr udp_send_flags_t udp_socket::dont_queue;
+constexpr udp_send_flags_t udp_socket::dont_fragment;
+
 }
diff --git a/src/utp_socket_manager.cpp b/src/utp_socket_manager.cpp
index 400d62d91..bbb4347c2 100644
--- a/src/utp_socket_manager.cpp
+++ b/src/utp_socket_manager.cpp
@@ -140,7 +140,7 @@ namespace libtorrent {
 
 	void utp_socket_manager::send_packet(std::weak_ptr<utp_socket_interface> sock
 		, udp::endpoint const& ep, char const* p
-		, int const len, error_code& ec, int flags)
+		, int const len, error_code& ec, udp_send_flags_t const flags)
 	{
 #if !defined TORRENT_HAS_DONT_FRAGMENT && !defined TORRENT_DEBUG_MTU
 		TORRENT_UNUSED(flags);
@@ -152,7 +152,7 @@ namespace libtorrent {
 #endif
 
 		m_send_fun(sock, ep, {p, std::size_t(len)}, ec
-			, ((flags & dont_fragment) ? udp_socket::dont_fragment : 0)
+			, (flags & udp_socket::dont_fragment)
 				| udp_socket::peer_connection);
 	}
 
diff --git a/src/utp_stream.cpp b/src/utp_stream.cpp
index 4b84717f5..30e20571c 100644
--- a/src/utp_stream.cpp
+++ b/src/utp_stream.cpp
@@ -1964,7 +1964,7 @@ bool utp_socket_impl::send_pkt(int const flags)
 	error_code ec;
 	m_sm.send_packet(m_sock, udp::endpoint(m_remote_address, m_port)
 		, reinterpret_cast<char const*>(h), p->size, ec
-		, p->mtu_probe ? utp_socket_manager::dont_fragment : 0);
+		, p->mtu_probe ? udp_socket::dont_fragment : udp_send_flags_t{});
 
 	++m_out_packets;
 	m_sm.inc_stats_counter(counters::utp_packets_out);
@@ -1992,7 +1992,7 @@ bool utp_socket_impl::send_pkt(int const flags)
 		UTP_LOGV("%8p: re-sending\n", static_cast<void*>(this));
 #endif
 		m_sm.send_packet(m_sock, udp::endpoint(m_remote_address, m_port)
-			, reinterpret_cast<char const*>(h), p->size, ec, 0);
+			, reinterpret_cast<char const*>(h), p->size, ec, {});
 	}
 
 	if (ec == error::would_block || ec == error::try_again)