Transparent firewall bridge question

[jayva2002]

I reviewed the article here: https://docs.opnsense.org/manual/how-tos/transparent_bridge.html
and have a question I hope someone can answer.  I want to place this in front of another router with its own public ip address and still have the OPNsense firewall have a public ip address too.  Do I assign the OPNsense public ip address the management interface of the bridge and just firewall restrict it for security?   I wasn't sure from the article if this setup was really meant to go behind a router instead of in front of it.   
Basically I have three routers that need a filtering firewall in front of them without NAT.  Anyone know?   And thanks in advance. 

[bsindia]

I am configuring a transparent bridge and am having difficulty adding a Management interface to the bridge as per instructions on the Opnsense forum.

4. Assign a management IP/Interface
To be able to configure and manage the filtering bridge (OPNsense) afterwards, we will need to assign a new interface to the bridge and setup an IP address.

Go to Interfaces ‣ Assign ‣ Available network port, select the bridge from the list and hit +.

Filtering Bridge Step 4.png

The path to add the management interface does not exist. What do I need to do to add the management interface??

Burley Stinnett