@akbarziyad I don't think it will work. Under my experience the LAN port of the PoE injector is not good, only work with short Ethernet cables.

@paulrob Can your IPv6 service work with this ER605 in standalone mode? Maybe try to upgrade the ER605 firmware. ER605 with old firmware does not support IPv6. I purchased an ER605 in 2021 early and...

@GoPokes1 Do you have public IP on both router's WAN? If you have NAT in front of tp-link router, you will need to do port forwarding 500/4500 for the tp-link router WAN IP.

@Pksparks Not sure if I understand your requirement. But if you have Omada controller, this example may be helpful: How to configure Multi-Networks & Multi-SSIDs on Omada SDN Controller

@fishdude If you have multi-nets, you need to configure static routing on main router. Also the router must support multi-net NAT. Check the example: How to build up a multi-nets network via...

@om3 Yes, the easiest way is to replace the MC210CS to MC220L so it can fit the TL-SM311LM. Another solution is to purchase switch with SFP ports, so you can connect TL-SM311LM and the fiber to the...