diff --git a/src/network/network_stun.cpp b/src/network/network_stun.cpp
new file mode 100644
--- /dev/null
+++ b/src/network/network_stun.cpp
@@ -0,0 +1,140 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file network_stun.cpp STUN sending/receiving part of the network protocol. */
+
+#include "../stdafx.h"
+#include "../debug.h"
+#include "network.h"
+#include "network_coordinator.h"
+#include "network_stun.h"
+
+#include "../safeguards.h"
+
+/** Connect to the STUN server. */
+class NetworkStunConnecter : public TCPConnecter {
+private:
+	ClientNetworkStunSocketHandler *stun_handler;
+	std::string token;
+	uint8 family;
+
+public:
+	/**
+	 * Initiate the connecting.
+	 * @param stun_handler The handler for this request.
+	 * @param connection_string The address of the server.
+	 */
+	NetworkStunConnecter(ClientNetworkStunSocketHandler *stun_handler, const std::string &connection_string, const std::string &token, uint8 family) :
+		TCPConnecter(connection_string, NETWORK_STUN_SERVER_PORT, NetworkAddress(), family),
+		stun_handler(stun_handler),
+		token(token),
+		family(family)
+	{
+	}
+
+	void OnFailure() override
+	{
+		this->stun_handler->connecter = nullptr;
+
+		/* Connection to STUN server failed. For example, the client doesn't
+		 * support IPv6, which means it will fail that attempt. */
+
+		_network_coordinator_client.StunResult(this->token, this->family, false);
+	}
+
+	void OnConnect(SOCKET s) override
+	{
+		this->stun_handler->connecter = nullptr;
+
+		assert(this->stun_handler->sock == INVALID_SOCKET);
+		this->stun_handler->sock = s;
+
+		/* Store the local address; later connects will reuse it again.
+		 * This is what makes STUN work for most NATs. */
+		this->stun_handler->local_addr = NetworkAddress::GetSockAddress(s);
+
+		/* We leave the connection open till the real connection is setup later. */
+	}
+};
+
+/**
+ * Connect to the STUN server over either IPv4 or IPv6.
+ * @param token The token as received from the Game Coordinator.
+ * @param family What IP family to use.
+ */
+void ClientNetworkStunSocketHandler::Connect(const std::string &token, uint8 family)
+{
+	this->token = token;
+	this->family = family;
+
+	this->connecter = new NetworkStunConnecter(this, NetworkStunConnectionString(), token, family);
+}
+
+/**
+ * Send a STUN packet to the STUN server.
+ * @param token The token as received from the Game Coordinator.
+ * @param family What IP family this STUN request is for.
+ * @return The handler for this STUN request.
+ */
+std::unique_ptr<ClientNetworkStunSocketHandler> ClientNetworkStunSocketHandler::Stun(const std::string &token, uint8 family)
+{
+	auto stun_handler = std::make_unique<ClientNetworkStunSocketHandler>();
+
+	stun_handler->Connect(token, family);
+
+	Packet *p = new Packet(PACKET_STUN_SERCLI_STUN);
+	p->Send_uint8(NETWORK_COORDINATOR_VERSION);
+	p->Send_string(token);
+	p->Send_uint8(family);
+
+	stun_handler->SendPacket(p);
+
+	return stun_handler;
+}
+
+NetworkRecvStatus ClientNetworkStunSocketHandler::CloseConnection(bool error)
+{
+	NetworkStunSocketHandler::CloseConnection(error);
+
+	/* If our connecter is still pending, shut it down too. Otherwise the
+	 * callback of the connecter can call into us, and our object is most
+	 * likely about to be destroyed. */
+	if (this->connecter != nullptr) {
+		this->connecter->Kill();
+		this->connecter = nullptr;
+	}
+
+	return NETWORK_RECV_STATUS_OKAY;
+}
+
+/**
+ * Check whether we received/can send some data from/to the STUN server and
+ * when that's the case handle it appropriately.
+ */
+void ClientNetworkStunSocketHandler::SendReceive()
+{
+	if (this->sock == INVALID_SOCKET) return;
+
+	/* We never attempt to receive anything on a STUN socket. After
+	 * connecting a STUN connection, the local address will be reused to
+	 * to establish the connection with the real server. If we would be to
+	 * read this socket, some OSes get confused and deliver us packets meant
+	 * for the real connection. It appears most OSes play best when we simply
+	 * never attempt to read it to start with (and the packets will remain
+	 * available on the other socket).
+	 * Protocol-wise, the STUN server will never send any packet back anyway. */
+
+	this->CanSendReceive();
+	if (this->SendPackets() == SPS_ALL_SENT && !this->sent_result) {
+		/* We delay giving the GC the result this long, as to make sure we
+		 * have sent the STUN packet first. This means the GC is more likely
+		 * to have the result ready by the time our StunResult() packet
+		 * arrives. */
+		this->sent_result = true;
+		_network_coordinator_client.StunResult(this->token, this->family, true);
+	}
+}