I have designed over a dozen boards that use the W5500 for TCP communications over a LAN. I recently tried to access the W5500 on a board which was configured in TCP mode and was in the Listen state. If I use a browser (like IE11) over the LAN, there is no problem connecting to port 80 of the W5500. However, if I set up my Netgear FV318 router for port forwarding to port 80 of the same W5500, the router does not recognize that the port is open!!
I spent considerable time (and money) working with the tech support people at Netgear to verify that the problem was with the W5500 and not the router.
I further confirmed this problem when I attempted to connect to the W5500 through the LAN using an ESP-8266 Wi-Fi device. The ESP-8266 successfully connects to an IP camera on the LAN but fails to connect to the W5500 on the same LAN.
I would like to find someone who has anyone successfully used port forwarding with the W5500 as the target device.