10G network bridge WITH gigabit internet connection?

[chmedly]

I'm working on a setup where I have a server and two workstations. I need all 3 machines to reach the internet over their "built-in" gigabit nics. But I also want a high speed network between the machines. In an effort for simplicity (and minimum power draw) I've taken to the idea of using a dual port 10G SFP+ nic in the server rather than a stand alone 10G switch. I need a way for each workstation to reach each other over something faster than the gigabit internet connection. [See Diagram].

These machines are all running Linux Mint 21. I've tried configuring a bridge across the dual nic by adding a file to /etc/network/interfaces.d/ called bridge.

Code: Select all

 
    auto lo br0
    iface lo inet loopback
    
    iface enp1 inet manual
    iface enp2 inet manual
    
    iface br0 inet static
    bridge_ports enp1 enp2
    address 192.168.7.1
    broadcast 192.168.7.255
    netmask 255.255.255.0
    gateway 192.168.7.254

This seems to mostly work. I'm able to export nfs from the server and mount it on a workstation. I'm able to ping both workstations at their 10G ip addresses from the server. I'm able to see and connect to an smb share from one workstation to another. But I'm not able to SSH from one workstation to the other.
More importantly, I'm having issues with the gigabit internet connection on the bridged machine (server). I can ping devices on the local gigabit network from the server but can't reach any websites. It almost seems that DNS is the culprit but I can't reach pages with their ip address either. Furthermore, mentioning a network interface in the interfaces/d file appears to cause the interface to disappear from the network settings GUI in Mint. (Yes, I'm running a desktop on the server) If I try to configure the gigabit nic via the interfaces.d file I still can't get working internet, even when setting the DNS server there.

I'm looking for a solution to get all the networks working.