try both ipv4 and ipv6 NTCP2 addresses if presented

libi2pd/RouterInfo.cpp

@@ -935,6 +935,24 @@ namespace data
 			});
 	}
 
+	std::shared_ptr<const RouterInfo::Address> RouterInfo::GetPublishedNTCP2V4Address () const
+	{
+		return GetAddress (
+			[](std::shared_ptr<const RouterInfo::Address> address)->bool
+			{
+				return address->IsPublishedNTCP2 () && address->host.is_v4 ();
+			});
+	}
+		
+	std::shared_ptr<const RouterInfo::Address> RouterInfo::GetPublishedNTCP2V6Address () const
+	{
+		return GetAddress (
+			[](std::shared_ptr<const RouterInfo::Address> address)->bool
+			{
+				return address->IsPublishedNTCP2 () && address->host.is_v6 ();
+			});
+	}	
+		
 	std::shared_ptr<RouterProfile> RouterInfo::GetProfile () const
 	{
 		if (!m_Profile)

libi2pd/RouterInfo.h

@@ -154,6 +154,8 @@ namespace data
 			int GetVersion () const { return m_Version; };
 			Addresses& GetAddresses () { return *m_Addresses; }; // should be called for local RI only, otherwise must return shared_ptr
 			std::shared_ptr<const Address> GetNTCP2Address (bool publishedOnly,  bool v4only = true) const;
+			std::shared_ptr<const Address> GetPublishedNTCP2V4Address () const; 
+			std::shared_ptr<const Address> GetPublishedNTCP2V6Address () const; 
 			std::shared_ptr<const Address> GetSSUAddress (bool v4only = true) const;
 			std::shared_ptr<const Address> GetSSUV6Address () const;
 

libi2pd/Transports.cpp

@@ -389,13 +389,23 @@ namespace transport
 			peer.router = netdb.FindRouter (ident); // try to get new one from netdb
 		if (peer.router) // we have RI already
 		{
-			if (!peer.numAttempts) // NTCP2
+			if (peer.numAttempts < 2) // NTCP2, 0 - ipv6, 1- ipv4
 			{
-				peer.numAttempts++;
 				if (m_NTCP2Server) // we support NTCP2
 				{
-					// NTCP2 have priority over NTCP
+					std::shared_ptr<const RouterInfo::Address> address;
-					auto address = peer.router->GetNTCP2Address (true, !context.SupportsV6 ()); // published only
+					if (!peer.numAttempts) // NTCP2 ipv6
+					{
+						if (context.SupportsV6 ())
+							address = peer.router->GetPublishedNTCP2V6Address ();
+						peer.numAttempts++;
+					}
+					if (!address && peer.numAttempts == 1) // NTCP2 ipv4	
+					{	
+						if (context.SupportsV4 ())
+							address = peer.router->GetPublishedNTCP2V4Address ();
+						peer.numAttempts++;
+					}	
 					if (address && !peer.router->IsUnreachable () && (!m_CheckReserved || !i2p::util::net::IsInReservedRange(address->host)))
 					{
 						auto s = std::make_shared<NTCP2Session> (*m_NTCP2Server, peer.router, address);
@@ -415,8 +425,10 @@ namespace transport
 						return true;
 					}
 				}
+				else
+					peer.numAttempts = 2; // switch to SSU
 			}
-			if (peer.numAttempts == 1)// SSU
+			if (peer.numAttempts == 2)// SSU
 			{
 				peer.numAttempts++;
 				if (m_SSUServer && peer.router->IsSSU (!context.SupportsV6 ()))