ETH0: xxx.xx.xx.13/30 (WAN block)
ETH1: xxx.xxx.xxx.17/28 (LAN block)
Create a DHCP server for LAN (eth1): xxx.xxx.xxx.16/28
With above your EdgeRouter will work as a pure router. Not firewall or something else.
Any device you connect to ETH1 will get a public IP-adress unprotected...