The hardware is nice, The software is not working or is not communicating properly with the hardware if I create a new subnet (completely different from the default lan) under lan and set it to port 8

My network included an Huawei HG8247h ONT and ER7212PC 1. HG8247h ONT in Router mode Everything works fine when HG8247h working in Router mode , and DHCP server on LAN side. The WAN port of ER7212PC g