check if we can send HolePunch to partcular address

libi2pd/SSU2.cpp

@@ -109,6 +109,21 @@ namespace transport
 			m_AddressV6 = localAddress;
 	}	
 
+	bool SSU2Server::IsSupported (const boost::asio::ip::address& addr) const
+	{
+		if (addr.is_v4 ())
+		{	
+			if (m_SocketV4.is_open ()) 
+				return true;
+		}	
+		else if (addr.is_v6 ())
+		{	
+			if (m_SocketV6.is_open ()) 
+				return true;
+		}
+		return false;
+	}	
+		
 	boost::asio::ip::udp::socket& SSU2Server::OpenSocket (const boost::asio::ip::udp::endpoint& localEndpoint)
 	{
 		boost::asio::ip::udp::socket& socket = localEndpoint.address ().is_v6 () ? m_SocketV6 : m_SocketV4;

libi2pd/SSU2.h

@@ -49,6 +49,7 @@ namespace transport
 			void Stop ();
 			boost::asio::io_service& GetService () { return GetIOService (); };
 			void SetLocalAddress (const boost::asio::ip::address& localAddress);
+			bool IsSupported (const boost::asio::ip::address& addr) const;
 		
 			void AddSession (std::shared_ptr<SSU2Session> session);
 			void RemoveSession (uint64_t connID);

libi2pd/SSU2Session.cpp

@@ -1344,7 +1344,12 @@ namespace transport
 				{
 					auto addr = ep.address ().is_v6 () ? r->GetSSU2V6Address () : r->GetSSU2V4Address ();
 					if (addr)
-						SendHolePunch (bufbe32toh (buf + 33), ep, addr->i);
+					{
+						if (m_Server.IsSupported (ep.address ()))
+							SendHolePunch (bufbe32toh (buf + 33), ep, addr->i);
+						else
+							code = eSSU2RelayResponseCodeCharlieUnsupportedAddress;
+					}	
 					else
 					{
 						LogPrint (eLogWarning, "SSU2: RelayInfo unknown address");

libi2pd/SSU2Session.h

@@ -108,6 +108,7 @@ namespace transport
 	{
 		eSSU2RelayResponseCodeAccept = 0,
 		eSSU2RelayResponseCodeBobRelayTagNotFound = 5,
+		eSSU2RelayResponseCodeCharlieUnsupportedAddress = 65,
 		eSSU2RelayResponseCodeCharlieSignatureFailure = 67,
 		eSSU2RelayResponseCodeCharlieAliceIsUnknown = 70
 	};