I am creating two separate network within RB450G where:

1. LAN1 - private home network on Ether 2 with IP 10.0.X.X/24. This port has its own DHCP Server (dhcp1), Ether 3 and Ether 4 are switched to master Ether 2, as well as have a VLAN.

2. LAN2 - private home guess network on Ether 5 with IP 172.18.X.X/24. This port has its own DHCP Server (dhcp2).

Both LAN1 and LAN2 are connected to Ether1 - WAN via Bridge1 on static !P 10.8.X.X. Would preferred to have two separate bridges however, when I tried linking WAN with a separate bridge to LAN2, the RB450G complains that a bridge on Ether 1 already exist...now I am thinking maybe I need to put the bridge on LAN1 and LAN2 connecting both to Ether1.

Question: how to make this work? I want to create firewall that applies to both IP addresses using the Address List. So far, I have LAN1's DHCP Server set up but the RB450G doesn't seem to like it (it's in RED font). Thank you in advance

You should not put your WAN interface in a bridge.

You just need to create your two separate LANs then just masquerade (NAT) out your WAN interface. Then you can set your firewall up as you would like.