Pretty close. Trusted hosts SHOULD be hosts that are A.,trusted and B., require access to those devices. So as an example "TRUSTES_HOSTS" could be management stations, admin desktops, or whatever is required to have access and you is "trusted". Ideally infrastructure address space should only be reachable from trusted users that need access and no one else. Infrastructure space would likely include addresses for routers, firewalls, switches , authentication servers, monitoring servers, basically anything that makes the network run and keeps it alive. Hope this helps.