If your network is not connected to the Internet, you create your own named.ca file. To do this, you designate one of your servers to be the root server, then create a named.ca file on every DNS server pointing to that root server.
For example, suppose your domain is named private and you designate the machine ourroot as your non-Internet root server. The ourroot machine has an IP address of 18.104.22.168. Your named.ca files would then contain the line:
ourroot.private. 999999 IN A 22.214.171.124
Cache files also need an SOA record, NS records for each domain and subdomain, and A records for each server.
; @ IN SOA ourroot.private. hermit.ourroot.private ( 1997071401 ; serial number (YYYYMMDD##) 10800 ; refresh after 3 hours 3600 ; retry after 1 hour 604800 ; expire after 1 week 86400 ) ; minimum TTL of 1 day ; ourroot.private. 999999 IN A 126.96.36.199 ; private. IN NS ourprimary.private. 1.1.192.in-addr.arpa IN NS ourprimary.private. ourprivate.private. IN A 188.8.131.52 ; private. IN NS oursecondary.private. 1.1.192.in-addr.arpa IN NS ourseconary.private. oursecondary.private. IN A 184.108.40.206
See "Setting Up a Non-Internet Root Master" for a more complete discussion of setting up a domain that is not connected to the Internet.