If you are connected to the Internet, use the root servers
already available. (For a list of root servers, use anonymous ftp to get the file /domain/named.ca from nic.ddn.mil.) However, if you are on an isolated network,
you must set up your own root servers.
A root server does not have a cache line in its boot file.
Instead, it has a line like this, which indicates that the server
is primary for the root domain:
The db.root file typically contains only NS and A resource records for the authoritative name space
tree. You can use the hosts_to_named command with the -r option to create the db.root file. Type man hosts_to_named for more information.
The db.cache file on the other name servers in the domain should contain
an entry for this root server.
A domain may have more than one root name server.
Following is an example of the root zone file, db.root. In the example db.root file, hosts rabbit.div.inc.com, denny.dept.inc.com, and sally.doc.inc.com are authoritative name servers for the root domain. Hosts eduardo.inc.com and labs.inc.com are authoritative for the inc.com subdomain.
|  @              IN      SOA     rabbit.div.inc.com.root.moon.div.inc.com. (
 
 3         ; Serial
 
 10800     ; Refresh after 3 hours
 
 3600      ; Retry after 1 hour
 
 604800    ; Expire after 1 week
 
 86400 )   ; Minimum ttl of 1 day
 
 IN   NS        rabbit.div.inc.com.
 
 IN   NS        denny.dept.inc.com.
 
 IN   NS        sally.dept.inc.com.
 
 rabbit.div.inc.com.   86400   IN   A         15.19.8.119
 
 denny.dept.inc.com.   86400   IN   A         15.19.15.33
 
 sally.doc.inc.com.    86400   IN   A         15.19.9.17
 
 ; ; set ttl to 3 days ;
 
 inc.com.              259200  IN   NS        eduardo.inc.com.
 
 25920   IN   NS        labs.inc.com.
 
 15.in-addr.arpa.      259200  IN   NS        eduardo.inc.com.
 
 259200  IN   NS        labs.inc.com.
 
 eduardo.inc.com.      259200  IN   A         15.19.11.2
 
 labs.inc.com.         259200  IN   A         15.19.13.7
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