The simplest thing that might work is any old computer with an ethernet port and one of these: https://en.wikipedia.org/wiki/List_of_router_and_firewall_distri

The simplest thing that might work is any old computer with an ethernet port and one of these: https://en.wikipedia.org/wiki/List_of_router_and_firewall_distributions https://en.wikipedia.org/wiki/List_of_router_and_firewall_di...