you can simply add : 188.8.131.52/20 as ip & the subnet mask , it wont affect anything on your network
it will allow only the domain controllers to talk to each other …
you can add a new site with new subnet config
this is a way to manage your sites also …
Keep in mind that the IP Subnets that you picked for your private network are actually routeable public IPs. Your users won’t be able to access sites which are hosted on those public IPs.