I work for a company that makes IoT devices. If one of our Ethernet IoT devices is connected to the RUT955, the router stops responding to the IoT device after about 10 minutes of no Ethernet packet activity. The IoT device sends sensor readings every 15 minutes to the cloud, it also obtains an SNTP update every 10 minutes. When the RUT955 stops responding it ignores the DNS lookup for the SNTP update, and when the readings are to be sent it also ignores that DNS lookup. It starts working again if there is a DHCP update.
I have been able to keep the system running by programming the RUT955 to send a ping to the IoT device every minute (the RUT955 ignores the response). I have also been able to keep it running by programming the RUT955 WAN Ethernet port to LAN and connecting the IoT device to this port. Due to the nature of our customers application and the volume of devices being sold, we need to do all we can to insure problem free operation.
The IoT device uses the LAN8740AI Ethernet PHY chip from SMSC. We have 2 other Ethernet products that use the ENC424J600 Ethernet PHY chip from Microchip, both work without issues.
Any help would be appreciated.