By default the CAS server will try to resolve the server names by using the DNS server that is configured for your windows instance. If this is not the one you want to use your own in the advanced properties editor.
You can aslo use a flat file in the config folder if you don't have a DNS that can resolve the names.
You can also check the DNS status by going to the CAS diagnostics console and running show dns status
I am facing a scenario where I need to display a server name that is different from the DNS result. Can the flat file you mentioned be used to override the DNS lookup? If so, which file needs to be updated and is there a particular format required?