Hi, I posted a similar question in another email but title was not appropriate, let me try it here using a more accurate clear title. I might need separate it into email questions, I am not quite clear it is boost socket nature or it is NAT issue. I have both client server applications using boost asio TCP socket, the client application is a Linux embedded system IoT device installed in home connect to server via NAT, the embedded system has two network interfaces, WiFi and cellular, in anytime there is only one network interface is up ans signed by an IP address, when one interface is down, another interface is up and signed IP address. The problem for an existing TCP socket connection is it cannot change from one interface to another. When one interface down another interface takes over, the client application continual sends data to the down interface buffered in TCP queue without transmission error but the server would never receive the data. It seems the only solution is to use QUIC, hence I asked here if there is any boost functions to support QUIC I can replace the TCP socket by QUIC. Appreciate your advice and tips. Thank you. Kind regards, - jupiter