diff --git a/daemon/HTTPServer.cpp b/daemon/HTTPServer.cpp
index 0847f85d..89960e0c 100644
--- a/daemon/HTTPServer.cpp
+++ b/daemon/HTTPServer.cpp
@@ -263,6 +263,9 @@ namespace http {
 					case eRouterErrorOffline:
 						s << " - Offline";
 					break;
+					case eRouterErrorSymmetricNAT:
+						s << " - Symmetric NAT";
+					break;	
 					default: ;
 				}
 				break;
diff --git a/libi2pd/RouterContext.h b/libi2pd/RouterContext.h
index 3c8e6d9d..228da788 100644
--- a/libi2pd/RouterContext.h
+++ b/libi2pd/RouterContext.h
@@ -39,7 +39,8 @@ namespace i2p
 	{
 		eRouterErrorNone = 0,
 		eRouterErrorClockSkew = 1,
-		eRouterErrorOffline = 2 
+		eRouterErrorOffline = 2,
+		eRouterErrorSymmetricNAT = 3
 	};
 
 	class RouterContext: public i2p::garlic::GarlicDestination
diff --git a/libi2pd/SSU.h b/libi2pd/SSU.h
index b674e8ac..bfcfed4e 100644
--- a/libi2pd/SSU.h
+++ b/libi2pd/SSU.h
@@ -63,6 +63,7 @@ namespace transport
 			void DeleteAllSessions ();
 
 			boost::asio::io_service& GetService () { return m_Service; };
+			uint16_t GetPort () const { return m_Endpoint.port (); };
 			void SetLocalAddress (const boost::asio::ip::address& localAddress);
 			
 			void Send (const uint8_t * buf, size_t len, const boost::asio::ip::udp::endpoint& to);
diff --git a/libi2pd/SSUSession.cpp b/libi2pd/SSUSession.cpp
index 8db317ed..e1e48b75 100644
--- a/libi2pd/SSUSession.cpp
+++ b/libi2pd/SSUSession.cpp
@@ -684,6 +684,8 @@ namespace transport
 		buf += 2; // our port
 		LogPrint (eLogInfo, "SSU: Our external address is ", ourIP.to_string (), ":", ourPort);
 		i2p::context.UpdateAddress (ourIP);
+		if (ourPort != m_Server.GetPort ())
+			i2p::context.SetError (eRouterErrorSymmetricNAT);
 		uint32_t nonce = bufbe32toh (buf);
 		buf += 4; // nonce
 		auto it = m_RelayRequests.find (nonce);