Some workings of how Domain Name Servers work

By Web Hosting Union

   The programs that store information about the domain name space are
   called name servers. Name servers generally have complete information
   about some part of the domain name space, called a zone, which they
   load from a file or from another name server. The name server is then
   said to have authority for that zone. Name servers can be
   authoritative for multiple zones, too.
  
   The difference between a zone and a domain is important, but subtle.
   All top-level domains, and many domains at the second level and lower,
   like berkeley.edu and hp.com, are broken into smaller, more manageable
   units by delegation. These units are called zones. The edu domain,
   shown in Figure 2.8, is divided into many zones, including the
   berkeley.edu zone, the purdue.edu zone, and the nwu.edu zone. At the
   top of the domain, there's also an edu zone. It's natural that the
   folks who run edu would break up the edu domain: otherwise, they'd
   have to manage the berkeley.edu subdomain themselves. It makes much
   more sense to delegate berkeley.edu to Berkeley. What's left for the
   folks who run edu? The edu zone, which would contain mostly delegation
   information to subdomains of edu.

  
   The berkeley.edu subdomain is, in turn, broken up into multiple zones
   by delegation, as shown in Figure 2.9. There are delegated subdomains
   called cc, cs, ce, me, and more. Each of these subdomains is delegated
   to a set of name servers, some of which are also authoritative for
   berkeley.edu. However, the zones are still separate, and may have a
   totally different group of authoritative name servers.
  
 
   A zone contains the domain names that the domain with the same domain
   name contains, except for domain names in delegated subdomains. For
   example, the top-level domain ca (for Canada) may have the subdomains
   ab.ca, on.ca, and qc.ca, for the provinces Alberta, Ontario, and
   Quebec. Authority for the ab.ca, on.ca, and qc.ca domains may be
   delegated to name servers in each of the provinces. The domain ca
   contains all the data in ca plus all the data in ab.ca, on.ca, and
   qc.ca. But the zone ca contains only the data in ca (see Figure 2.10),
   which is probably mostly pointers to the delegated subdomains.
  
   If a subdomain of the domain isn't delegated away, however, the zone
   contains the domain names and data in the subdomain. So the bc.ca and
   sk.ca (British Columbia and Saskatchewan) subdomains of the ca domain
   may exist, but might not be delegated. (Perhaps the provincial
   authorities in B.C. and Saskatchewan aren't yet ready to manage their
   subdomains, but the authorities running the top-level ca domain want
   to preserve the consistency of the name space and implement subdomains
   for all the Canadian provinces right away.) In this case, the zone ca
   has a ragged bottom edge, containing bc.ca and sk.ca, but not the
   other ca subdomains, as shown in Figure 2.11.