Single IP Subnet on WAN - How?

[mattyakel]

I'm trying to replace a Cisco RV325 Dual WAN Gigabit Router with pfSense for a client network. They have a /28 publicly routable IP subnet. The current setup is that there is 1 WAN interface on the Cisco and 1 'DMZ/WAN2' interface.

Example:
1.2.3.98/28 (obviously this isn't actually their public IP address. )

1.2.3.96/28 - Network
255.255.255.240 - netmask
1.2.3.111 - broadcast
1.2.3.97-110 - usable

1.2.3.98 -- WAN on Cisco/pfSense
1.2.3.97 -- ISP Gateway
1.2.3.103 -- PBX (Statically assigned on device, I can't change this one.)

The Cisco's 'DMZ/WAN2' interface if you turn on DMZ I can just allow 1.2.3.99 - 1.2.3.110 to just be passed through on that port, so any device I have downstream on that interface I can statically assign a public IP in the available range and it just works.

With pfSense I bridged the WAN & OPT1 interfaces and the PBX can't get out on the internet. I've tried using this page from the docs as a guide but there's something that I'm missing some where.

https://docs.netgate.com/pfsense/en/latest/book/firewall/methods-of-using-additional-public-ip-addresses.html#single-ip-subnet-on-wan

Do I have to just waste a public IP to assign to the "CARP VIP" I don't understand how that the VIP helps with the box that's connected to OPT1 interface.

I Also looked at an actual DMZ following Jim's video from the Netgate YT channel. https://youtu.be/QFk5jX-oeSo per his notes on the slides you have to have a separate publicly routable subnet to assign to the DMZ or you have to do 1:1 NAT where your "DMZd" devices have a private IP and then just 1:1 to an available Public IP. I only have a single public subnet.

Does anyone know how to accomplish this? I feel like there is something that I'm missing, I thought this would be an easier problem to solve. Any help would be greatly appreciated. Thanks.