The cache Line

A name server needs to know which servers are the authoritative name servers for the root zone. To do this, you have to list the addresses of these higher authorities.

All servers should have the following line in the boot file to find the root name servers:

cache    .     named.ca

The first field after cache (.) indicates that the server will obtain root servers hints from the indicated file, in this case, named.ca (located in the directory /var/named).