LAN and WAN separate networks for Mac OS

We have installed an iMac, ATEM 1 M/E 4k, Switcher Advance Panel, CCU Advance Panel, and HyperDeck system. All elements daisy chain to the iMac via network cable and a thunderbolt network dongle #1. We call this our LAN network. All is good.

We now want to connect the iMac to the Internet via a thunderbolt to network dongle #2 and have this as our WAN network. We want the Blackmagic system to stay separate and not be recognized on the Internet/WAN network. Our IT folks would prefer this setup. Would anyone like to suggest a best method in the Mac OS for separating the two networks? We sure appreciate this forum and everyone's wonderful advice!

We have installed an iMac, ATEM 1 M/E 4k, Switcher Advance Panel, CCU Advance Panel, and HyperDeck system. All elements daisy chain to the iMac via network cable and a thunderbolt network dongle #1. We call this our LAN network. All is good.

We now want to connect the iMac to the Internet via a thunderbolt to network dongle #2 and have this as our WAN network. We want the Blackmagic system to stay separate and not be recognized on the Internet/WAN network. Our IT folks would prefer this setup. Would anyone like to suggest a best method in the Mac OS for separating the two networks? We sure appreciate this forum and everyone's wonderful advice!

just plug in the second interface, and order it first in the networks list

Also learning from Apple that the iMac ethernet on the back of the computer or located on the inline power transformer is on a separate bus from a thunderbolt port and Apple confirmed the OS does not share information between the WAN and LAN networks. Thanks for the help!