Help with a Triple Router in a Y-Configuration

Help with a Triple Router in a Y-Configuration

Hello everyone,

This is what I am thinking; tell me if I am off the wall with this.
Cable modem: Surfboard extreme SB6120
it will be time to upgrade the Cable modem before long.

Router 1: TP-Link TL-ER5120 DHCP Server

Router 2: TP-Link TL-ER5120 LAN

Router 3: TP-Link TL-ER5120 WAN

My RT-AC88U goes into the WAN of Router 3


Thank You for your help…