Network Devices — USB Ethernet Adapter

I got a network configuration problem. I got one machine that have two network cards (wired Ethernet) NIC 1 - DHCP 8x.x.x.x                    Internet access only (through a external firewall) NIC 2 - Static IP 172.16.100.133   Local network but Internet access is possible, but this machine should not used it for that NIC 1 gets into the "Public network" category NIC 2 gets into the "Private network" category The problem is that I do not want internet traffic to go out on NIC2, Only 172.16.*  But sometimes the routing get messed...

The two connections are on the same IP segment. They are configured in Linux with no IP address. Traffic will be bridged across the 2 ports as shown in the diagram. The USB to Dual Ethernet cable is attached to a USB 3.0 port on a Raspberry Pi running Debian 10 Buster.When I power on the Raspberry Pi we see only one ethernet interface on the adapter. When I unplug the adapter, and connect to another USB3.0 port on the Raspberry Pi, both ethernet interfaces appear under Linux.Once both ethernet interfaces are found, the cable operate in bridge more with no...