I think all those are anti-features on a network slug. As I understand it, the device is intentionally simple because it is there to ensure some misconfiguratio

I think all those are anti-features on a network slug. As I understand it, the device is intentionally simple because it is there to ensure some misconfiguration cannot expose some port that should not be exposed. I have implemented firewalls similar to this in the past. They typically had three network interfaces. Two of them were configured as bridges and then I use ebtables/iptables to filter traffic flowing through. These two interfaces would have no IP address and would not be visible on a traceroute, etc. The third interface would only be connected to a separate admin network. Or it might not even be plugged in. In the latter case, the admin needing to change anything on the device would have to be physically present and bring a "crossover" ethernet cable and plug their laptop directly into the third NIC of the firewall. From there, they would be able to ssh into the firewall and change config.